[Federal Register Volume 69, Number 6 (Friday, January 9, 2004)]
[Rules and Regulations]
[Pages 1620-1641]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-427]



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Part II





Department of Transportation





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Federal Aviation Administration



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14 CFR Parts 1, 91, et al.



Enhanced Flight Vision Systems; Final Rule

  Federal Register / Vol. 69, No. 6 / Friday, January 9, 2004 / Rules 
and Regulations  

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 1, 91, 121, 125, and 135

[Docket No. FAA-2003-14449; Amendment Nos. 1-52; 91-281; 121-303; 125-
45; 135-93]
RIN 2120-AH78


Enhanced Flight Vision Systems

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is revising its regulations for landing under 
instrument flight rules to allow aircraft to operate below certain 
specified altitudes during instrument approach procedures, even when 
the airport environment is not visible using natural vision, if the 
pilot uses certain FAA-certified enhanced flight vision systems. This 
action informs the public and the aviation industry of the approval of 
the use of new technology for certain operational benefits.

DATE: Effective February 9, 2004.

FOR FURTHER INFORMATION CONTACT: Les Smith, Flight Technologies and 
Procedures Division, Flight Standards Service, AFS-400, Federal 
Aviation Administration, 800 Independence Ave. SW., Washington, DC 
20591; telephone: (202) 385-4586.

SUPPLEMENTARY INFORMATION:

Availability of Rulemaking Documents

    You can get an electronic copy of this document using the Internet 
by:
    (1) Searching the Department of Transportation's electronic Docket 
Management System (DMS) Web page (http://dms.dot.gov); do a Simple 
Search for ``14449.''
    (2) Visiting the Office of Rulemaking's Web page at http://www.faa.gov/avr/arm/index.htm or
    (3) Accessing the Government Printing Office's Web page at http://www.access.gpo.gov/su_docs/aces/aces140.html.
    You can also get a copy by submitting a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue, SW., Washington, DC 20591, or by calling (202) 267-9680. Be 
sure to identify docket number FAA-2003-14449, or the title of this 
final rule, ``Enhanced Flight Vision Systems.''
    Anyone is able to search the electronic form of all comments 
received into any of our dockets by the name of the individual 
submitting the comment (or signing the comment, if submitted on behalf 
of an association, business, labor union, etc.). You may review DOT's 
complete Privacy Act statement in the Federal Register published on 
April 11, 2000 (Volume 65, Number 70, pages 19477-78) or you may visit 
http://dms.dot.gov.

Small Business Regulatory Enforcement Fairness Act

    The Small Business Regulatory Enforcement Fairness Act (SBREFA) of 
1996 requires the FAA to comply with small entity requests for 
information or advice about compliance with statutes and regulations 
within its jurisdiction. Therefore, any small entity that has a 
question regarding this document may contact its local FAA official, or 
the Office of Rulemaking at (202) 267-8487. You can find out more about 
SBREFA on the Internet at http://www.faa.gov/avr/arm/sbrefa.htm, or by 
e-mailing us at [email protected].

List of Abbreviations Used in This Document

AC--Advisory circular
AGL--Above ground level
ASR--Airport surveillance radar
AWO--All-weather operations
DH--Decision height
EFV--Enhanced flight visibility
EFVS--Enhanced flight vision system
EVS--Enhanced vision system
FPV--Flight path vector
FSB--Flight Standardization Board
HAT--Height above touchdown
HUD--Head-up display
IFR--Instrument flight rules
ILS--Instrument landing system
JAA--Joint Aviation Authorities
MDA-Minimum descent altitude
PAR--Precision approach radar
RNAV--Area navigation
SAE--Society of Automotive Engineers
SVS--Synthetic vision system
TAOARC--Terminal Area Operations Aviation Rulemaking Committee
TERPS--U.S. Standard for Terminal Instrument Procedures
TSO--Technical Standard Order
VOR--Very high frequency omnirange station
VDP--Visual descent point

Outline of Preamble

I. Background
II. Discussion of the Proposed Rule
III. Related Rulemaking Actions
IV. Discussion of Comments
IV.1. General
    IV.2. Flight visibility and visual references
    IV.3. Visual cues (visual references)
    IV.4. Restricted visual references
    IV.5. Harmonization
    IV.6. Airport lighting systems
    IV.7. Electromagnetic spectrum
    IV.8. Limitations of systems
    IV.9. Other technologies
    IV.10. Regulatory Bar To Use of Systems Such as SVS
    IV.11. Differentiation between runway and taxiway
    IV.12. Obstacle clearance
    IV.13. Weather-related comments
    IV.14. Equipment-related weather minimums
    IV.15. Operational intent of the rule
    IV.16. Operational benefits for part 121, part 125, and part 135 
operations
    IV.17. Part 121, part 135, and part 129 operations
    IV.18. Operational experience before credit for lower minimums
    IV.19. Takeoff minimums for EFVS
    IV.20. Rule should be an advisory circular (AC)
    IV.21. Terminology: Category I and Advisory Circulars
    IV.22. Coordination through TAOARC and AWO process
    IV.23. EFVS flight path performance
    IV.24. Inconsistency with terminology in AC 120.28D or AC 
120.29A
    IV.25. EFVS use for Category II and Category III approaches
    IV.26. Compliance with Sec.  91.1039
    IV.27. Definitions--Italicization and capitalization
    IV.28. Definitions--Scope of enhanced flight vision systems
    IV.29. Definitions--Examples of enhanced flight vision systems
    IV.30. Definitions--Enhanced flight vision systems
    IV.31. Definitions--Topography and enhanced flight vision 
systems
    IV.32. Synthetic vision systems
    IV.33. Enhanced ground visibility systems
    IV.34. Straight-in approaches
    IV.35. Flight visibility or enhanced flight visibility
    IV.36. Reduced approach minima
    IV.37. Natural vision
    IV.38. AC 120-29A
    IV.39. Reduced environment as a visual reference
    IV.40. Barometric altitude
    IV.41. Reliance on EFVS
    IV.42. Touchdown zone determination
    IV.43. Training
    IV.43.a. AFS and RFM limitations
    IV.43.b. No additional training
    IV.43.c. Additional training and proficiency
    IV.43.d. Crew training
    IV.44. Requirements for the Airplane Flight Manual (AFM)
    IV.45. Air carrier operations specifications requirements
    IV.46. Foreign aircraft certification
    IV.47. Equipment requirements for subpart C
    IV.48. Clarification on maneuvering
    IV.49. Certification of an EFVS
    IV.50. Performance-based advisory materials
    IV.51. Display comments
    IV.51.a. Head-up or head-down displays
    IV.51.b. Head-up display
    IV.51.c. Guidance, flight path vector (FPV) and other symbology
    IV.51.d. EFVS for situational awareness
    IV.51.e. Design eye position
    IV.51.f. Display conformality and parallax errors

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    IV.51.g. Power system for an EFVS
    IV.51.h. Independent displays
    IV.52. Comments on economic evaluation
V. Contact with Aircraft Manufacturer for Confirmation of 
Performance Capabilities
VI. Differences Between the NPRM and Final Rule
VII. Discussion of Final Rule
VIII. Paperwork Reduction Act
IX. International Compatibility
X. Economic Evaluation
XI. Regulatory Flexibility Determination
XII. International Trade Impact Analysis
XIII. Unfunded Mandates Assessment
XIV. Executive Order 13132, Federalism
XV. Environmental Analysis
XVI. Energy Impact

I. Background

    Section 91.175 of 14 CFR contains the flight visibility 
requirements for conducting operations to civil airports using natural 
vision to identify the approach lights and runway environment. These 
instrument approach requirements have been modified over the years to 
provide for operating an aircraft during reduced visibility conditions 
while maintaining a high level of safety. The current rules on 
instrument approach procedures do not allow aircraft to operate below 
the decision height (DH) or minimum descent altitude (MDA) if the 
airport environment cannot be seen with natural vision. This final rule 
allows operators conducting other than Category II or Category III 
straight-in instrument approach procedures to operate below the DH and 
MDA when new technologies, such as an enhanced flight vision system 
(EFVS), use imaging-sensor technology that provides a real-time image 
of the external topography. During some reduced visibility conditions, 
an EFVS can display imagery that may significantly improve the pilot's 
capability to detect objects, such as approach lights and visual 
references of the runway environment that may not be visible. This 
final rule will allow, but not mandate, the use of this kind of 
technology.

II. Discussion of the Proposed Rule

    By notice of proposed rulemaking (NPRM) Notice No. 03-03, February 
10, 2003 (68 FR 6801), the FAA proposed to amend its rules to allow for 
the operational use of an EFVS, which can display imagery that may 
significantly improve the pilot's capability to detect objects that may 
not otherwise be visible. The FAA proposed that the provisions of this 
NPRM would apply to operations conducted under parts 91, 121, 125, 129, 
and 135. The comment period on the proposal closed March 27, 2003.
    In the NPRM, the FAA also proposed that the pilot of an aircraft 
could use this system to determine ``enhanced flight visibility'' while 
flying a straight-in standard instrument approach procedure. An EFVS 
would enable the pilot to determine ``enhanced flight visibility'' at 
the decision height (DH) or MDA, in lieu of ``flight visibility'' (as 
currently defined), by using a head-up display (HUD) to display sensor 
imagery of the approach lights or other visual references for the 
runway environment at a distance no less than the visibility prescribed 
in the instrument approach procedure being used.
    The FAA proposed to define ``enhanced flight visibility'' as the 
average forward horizontal distance, from the cockpit of an aircraft in 
flight, at which prominent topographical objects may be clearly 
distinguished and identified by day or night by a pilot using an EFVS. 
This definition would be substantially equivalent to the definition of 
flight visibility in part 1. The pilot would use this enhanced flight 
visibility and go through a similar decisionmaking process as required 
by existing Sec.  91.175 (c) to continue the approach from the DH or 
MDA down to 100 feet above the touchdown zone elevation of the runway 
of intended landing. At that point and below, certain things would have 
to be visible to the pilot without using the EFVS in order for the 
aircraft to proceed to a landing on the intended runway. This rule will 
permit but will not require the use of this technology.
    The proposed rule, therefore, could allow for operational benefits, 
reduced costs, and increased safety for aircraft equipped with an EFVS. 
Use of an EFVS with a HUD may improve the level of safety by improving 
position awareness, providing visual cues to maintain a stabilized 
approach, and minimizing missed approach situations. In addition to 
using an EFVS to satisfy new Sec.  91.175 (l) requirements, an EFVS may 
allow the pilot to observe an obstruction on the runway, such as an 
aircraft or vehicle, earlier in the approach, and observe potential 
runway incursions during ground operations in reduced visibility 
conditions. Even in situations where the pilot experiences the required 
flight visibility at the DH or MDA, he or she could still use an EFVS 
to have better situational awareness than may be possible without it 
especially in marginal visibility conditions.
    However, it should be noted that the NPRM did not propose to allow 
the use of a ``synthetic vision'' system as a means of determining the 
required enhanced flight visibility or to identify one of the visual 
references for the intended runway. Synthetic vision is a computer-
generated image of the external scene topography from the perspective 
of the flight deck that is derived from aircraft attitude, a high-
precision navigation solution, and a database of terrain, obstacles, 
and relevant cultural features. A synthetic vision system is an 
electronic means used to display a synthetic vision image of the 
external scene topography to the flight crew.

III. Related Rulemaking Actions

    In a separate rulemaking project, the FAA conducted a thorough 
review of its rules to ensure consistency between the operating rules 
of 14 CFR and future proposed area navigation (RNAV) operations for the 
National Airspace System (NAS). On December 17, 2002, the FAA published 
a proposed rule entitled, ``Area Navigation (RNAV) and Miscellaneous 
Amendments'' (67 FR 77326; Dec. 17, 2002). In that NPRM, the FAA 
proposed to enable the use of space-based navigation aid sensors for 
aircraft RNAV systems through all phases of flight (departure, en 
route, arrival, and approach) to enhance the safety and efficiency of 
the national airspace system.
    Because at the time the EFVS NPRM was issued, the comment period 
for the RNAV NPRM was still open, the FAA incorporated certain proposed 
terminology, such as ``approach procedure with vertical guidance 
(APV)'' and ``decision altitude (DA),'' from the RNAV NPRM into the 
EFVS NPRM. This is discussed in detail in the preamble to the EFVS NPRM 
(under ``Related NPRM'' at 68 FR 6803). The comment period on the RNAV 
proposed rule closed on July 7, 2003. The FAA received numerous 
comments on the terminology proposed in the RNAV NPRM, and must 
consider those comments before issuing a final rule. Since those 
comments are still under review, and the RNAV rulemaking action is not 
yet a final rule, the FAA is not adopting the RNAV-related language in 
the EFVS final rule.
    In addition, on April 8, 2003, the FAA adopted certain terms from 
the December 2002 RNAV NPRM by publishing a final rule, ``Designation 
of Class A, B, C, D, and E Airspace Areas; Air Traffic Service Routes; 
and Reporting Points' (68 FR 16943). The FAA also reorganized the 
structure of its regulations concerning the Designation of Class A, B, 
C, D, and E airspace areas, and it incorporated by reference two FAA 
Orders--8260.3, U.S. Standard for Terminal Instrument Procedures

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(TERPS) and 8260.19, Flight Procedures and Airspace. These portions of 
the December 2002 RNAV NPRM were issued as a final rule to facilitate 
the development of RNAV routes that are not restricted to ground-based 
navigation systems.

IV. Discussion of Comments

IV.1. General

    The FAA received more than 40 comments in response to the NPRM. 
Commenters supporting the proposed rule commended the FAA for 
developing a regulation to enable the use of enhanced visibility 
technology that will increase levels of safety, provide operational 
benefits, and increase aircraft operational efficiency. Some commenters 
also believed that through the use of EFVS, aircrews will experience 
increased situational awareness, improve approach completion rates, 
reduce operational costs and significantly increase IFR safety margins.
    Commenters opposed to the changes in the proposal requested that 
the FAA withdraw the NPRM because they asserted that the NPRM is 
inconsistent with current FAA advisory materials and the NPRM should be 
coordinated through one of the FAA's rulemaking committees, that have 
aviation industry participants. Some believed that the use of EFVS as 
proposed in the NPRM would be so restrictive that it would limit 
investment in vision system technologies and would limit the safety 
benefits of such systems.
    FAA's response: The FAA believes that the use of EFVS-equipped 
aircraft will provide operational benefits and increase aircraft 
operational efficiency in reduced visibility conditions. The FAA 
believes that the NPRM is consistent with advisory materials and that 
the best course for approval is to use the rulemaking process. The FAA 
does not believe that this rule limits investment in vision-sensor 
technologies. Responses to these and other issues are provided in 
greater detail in the following subject-by-subject discussions.

IV.2. Flight Visibility and Visual References

    Comment: There were several comments recommending the deletion of 
Sec.  91.175(c)(2) on flight visibility because the visibility 
determination is readily established in Sec.  91.175(c)(3) via 
identifiable airport lighting systems and/or environment. Commenters 
pointed out that the additional requirement of a pilot quantifying 
flight visibility (as defined in 14 CFR part 1) with no other means 
than a subjective determination adds an undue burden to the flight crew 
and no means of substantiation. A commenter asserted that this flight 
visibility requisite is especially an undue burden when the requirement 
of Sec.  91.175(c)(3) has been accomplished. Conversely, commenters 
suggested, continuation with an approach below the MDA or DH should be 
predicated on the ability to see the runway environment, not a 
numerical determination of the current flight visibility.
    FAA's response: The FAA disagrees with the recommendation to delete 
the ``flight visibility'' requirement of Sec.  91.175(c)(2) because the 
requirement still applies to instrument approach procedures not 
involving the use of EFVS. Not all operators will install an EFVS. 
However, in accordance with the requirements in Sec.  91.175(l)(2), 
this rule will allow the use of an EFVS to meet the requirement for 
determining enhanced flight visibility, which is substantially 
equivalent to the requirements in Sec.  91.175(c)(2). The intent of 
this rulemaking is to allow the use of enhanced flight vision systems 
to operate an aircraft below DH or MDA even when ``flight visibility'' 
requirements are not met. The FAA did not propose to change 
requirements that apply to non-EFVS operations. The origin of the term 
``flight visibility'' and ``visual references'' can be found in 
Amendment No. 91-173, (46 FR 2280, January 8, 1981). In that amendment 
of former Sec.  91.116 (recodified as Sec.  91.175 in 1989), the term 
``visibility'' was clarified with the introduction of the term ``flight 
visibility.'' Guidance was also provided for the specific ``visual 
references'' that the pilot must identify at the MDA or DH to continue 
the approach.
    Amendment No. 91-173 clarified the term ``visibility'' in Sec.  
91.116(c)(2) to specify that ``no pilot may operate an aircraft below 
MDA or DH unless the flight visibility is not less than the visibility 
prescribed in the standard instrument approach procedure being used.'' 
This revised requirement was necessary to make it clear that the 
visibility referred to is the visibility from the aircraft and not 
ground visibility. To simply state that, if the pilot has the runway in 
sight, the flight visibility requirement is satisfied, is not always 
valid. This concept may be valid for a Category I ILS approach but 
would not be valid for other straight-in approaches such as a very high 
frequency omnirange station (VOR) approach where the missed approach 
point (the VOR navaid) is located on the airport. For example, if the 
visibility for the VOR approach is 1 statute mile and the MDA is 600 
feet (assuming no approach light system), and the pilot of an airplane 
does not see the runway environment until passing over the runway 
threshold at 600 feet, the pilot would have met the criteria for 
identifying the runway, but with only 600 feet of visibility assured 
would typically not be in a position to safely maneuver the aircraft 
for a landing. In this hypothetical situation, the flight visibility is 
less than 1 statute mile. However, if the flight visibility had been 1 
statute mile, the pilot would have been able to identify the runway 
threshold or runway lights at a distance sufficient to make a normal 
rate of descent, using normal maneuvers from a visual descent point 
(depicted on the approach chart or determined by the pilot) and 
maneuver the aircraft for a landing. Simply saying that by identifying 
one of the visual references of Sec.  91.175(c)(3) satisfies the 
requirement for flight visibility, as stated on the instrument approach 
procedure, is not enough for a safe operation.
    It should be noted that the amendment to former Sec.  91.116 also 
made it clear that the pilot must have the prescribed flight visibility 
from descent below MDA or DH until touchdown by using as reference 
items such as approach lights, threshold, threshold markings, etc., 
instead of towers, smoke stacks, buildings, and other landmarks that 
may be located far from the end of the runway.
    The objective of this rulemaking is to allow the use of any FAA-
certified EFVS that can display a real-time image of the external scene 
topography and meet the requirements of Sec.  91.175(l) and (m). A 
proposed EFVS could meet the requirements of Sec.  91.175(l) and (m) 
and yet not be capable of distinguishing colors, and may not even be 
capable of detecting the approach light system or runway lights, but 
will provide an image of the runway surface and the metal structures 
that encompass the approach lights or runway lights.

IV.3. Visual Cues (Visual References)

    Comment: Several commenters also stated that the visual cues should 
not be restricted to the two listed in the EFVS NPRM for the final 
descent, but broadened to include any of those listed in Sec.  
91.175(c)(3).
    FAA's response: The FAA disagrees with these commenters. In the 
NPRM, the FAA proposed that in order for the pilot to descend below the 
DH or MDA when using the EFVS, one of two requirements had to be met: 
(1) The approach light system (if installed) had

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to be seen; or (2) both the threshold and the touchdown zone had to be 
seen. If the approach light system was not seen (e.g., because it was 
not installed or because it was not operating), the proposed rule would 
have required that the pilot see both the threshold and the touchdown 
zone in order to proceed below the DH or MDA. The FAA proposed a 
compound requirement (i.e., the threshold and the touchdown zone) to 
have a more stringent standard than what is allowed under existing 
Sec.  91.175(c)(3) when using natural vision. The FAA proposed and 
adopts in this final rule a more stringent standard because these EFVS 
devices might not display the color of the lights or the runway 
markings.
    As proposed and as adopted in this final rule, the FAA's safety 
goal was to specify certain visual references that would help the pilot 
determine whether the aircraft was properly aligned with the runway of 
intended landing. Thus, if the pilot using the EFVS can see the 
approach light system, this is adequate to determine whether the 
aircraft is properly aligned to continue the approach. If, on the other 
hand, for whatever reason, the approach light system cannot be seen, 
the FAA proposed, and finds that it is necessary, to have a compound 
visual cue (visual references) requirement of the threshold and the 
touchdown zone. The safety reason for this compound visual cue 
requirement is that EFVS may not be capable of displaying runway 
markings and the color of lights to identify the touchdown zone area of 
the runway. Having a threshold identifying cue in sight and a touchdown 
zone cue in sight should give the pilot an adequate pattern of 
recognition to determine whether the aircraft is properly aligned with 
a runway and thus, enable the pilot to determine whether to continue or 
to execute a missed approach.
    In the proposed Sec.  91.175(l)(3)(ii), the FAA used the language, 
``the runway threshold and the touchdown zone.'' In the final rule, for 
clarification purposes, the FAA is specifying those items that it 
considers as identifiers of the runway threshold and touchdown zone. 
Thus, in order to identify the runway threshold, the pilot needs to be 
able to see the beginning of the runway landing surface, the threshold 
lights, or the runway end identifier lights. In addition, in order to 
identify the runway touchdown zone, the pilot needs to see the runway 
touchdown zone landing surface, the touchdown zone lights, the 
touchdown zone markings, or the runway lights. When the FAA refers to 
``runway lights'' in Sec.  91.175(l)(3)(ii)(B)(4), this does not mean 
all of the runway lights. Instead, it means only those runway lights 
that together with the threshold identifier would help the pilot 
recognize whether he or she is approaching the runway of intended 
landing. Therefore, in this final rule, Sec.  91.175(l)(3) is revised 
to read as follows:

    (3) The following visual references for the intended runway are 
distinctly visible and identifiable to the pilot using the enhanced 
flight vision system:
    (i) The approach light system (if installed); or
    (ii) The following visual references in both paragraphs 
(l)(3)(ii)(A) and (B) of this section:
    (A) The runway threshold, identified by at least one of the 
following:
    (1) The beginning of the runway landing surface;
    (2) The threshold lights; or
    (3) The runway end identifier lights.
    (B) The touchdown zone, identified by at least one of the 
following:
    (1) The runway touchdown zone landing surface;
    (2) The touchdown zone lights;
    (3) The touchdown zone markings; or
    (4) The runway lights.

IV.4. Restricted Visual References

    Comment: One commenter noted that some visual references currently 
present in Sec.  91.175(c)(3) (for example, the runway end identifier 
lights, the runway or runway markings, and runway lights) would be lost 
to EFVS users under proposed Sec.  91.175(l)(4).
    FAA's response: The FAA does not agree. Section 91.175(c)(3) of the 
current regulations relate to a different set of circumstances than 
proposed Sec.  91.175(l)(4). In the EFVS NPRM and this rule, the pilot 
at 100 feet above the touchdown zone elevation of the runway of 
intended landing must see the lights or markings of the threshold or 
the lights or markings of the touchdown zone using natural vision. Some 
of the items listed in Sec.  91.175(c)(3) would not be visible at 100 
feet above the touchdown zone elevation.

IV.5. Harmonization

    Comment: A commenter pointed out that a stated goal of both the 
Joint Aviation Authorities (JAA) and the FAA is harmonization. This 
commenter believed that deleting the reference to flight visibility and 
continuing to use the visual references of Sec.  91.175(c)(3) would 
harmonize the FAA and JAA regulations.
    FAA's response: The topic of ``flight visibility'' could be a 
subject for future JAA harmonization discussions, but at this time 
there is no corresponding JAA provision. This comment is not within the 
scope of this rulemaking because the FAA did not propose to remove the 
requirement for flight visibility in Sec.  91.175(c)(2).

IV.6. Airport Lighting Systems

    Comment: Several commenters stated that the EFVS should be 
compatible with the airport lighting systems. One commenter noted that 
recent information indicates that some newly installed airport lighting 
systems will use current technology light emitting diode (LED) systems 
that do not have a large infrared signature. According to the 
commenter, these LED systems potentially are not visible to current 
enhanced vision systems (EVS).
    FAA's response: The FAA acknowledges that some EFVS may perform 
differently in detecting airport lighting systems. However, the rule 
provides the pilot with various other identifiers to meet the visual 
reference requirement of Sec.  91.175(l)(3). If the pilot is unable to 
identify any of the required visual references in Sec.  91.175(l)(3) 
with the EFVS at the DH or MDA, a missed approach must be conducted.

IV.7. Electromagnetic Spectrum

    Comment: One commenter noted that an EFVS may not be limited to 
operations outside the visible frequencies of the electromagnetic 
spectrum. This system restriction is omitted for the proposed 
definition of EFVS in 14 CFR part 1. This commenter recommends that the 
FAA disregard the last phrase in the NPRM preamble background 
discussion for ``Previous type designs'' that states `` * * * which 
operates outside the visible portion of the electromagnetic spectrum'' 
and allow the proposed EFVS definition to provide the description.
    FAA's response: The FAA agrees with this commenter that an EFVS may 
be designed to operate within the visible portion of the 
electromagnetic spectrum. The definition of an EFVS in part 1 does not 
prohibit these types of EFVS and therefore the rule does not have to be 
amended.

IV.8. Limitations of Systems

    Comment: One commenter proposed that the FAA add a concluding 
paragraph to the revision of proposed Sec.  91.175 in lieu of the 
proposed language that stated: ``Notwithstanding provisions of 
paragraphs above, the Administrator may approve the use of Enhanced 
Vision Systems (EVS) and procedures meeting requirements other than 
those specified, if: (1) The systems and procedures proposed are shown 
to have equivalent or better performance than other approved systems, 
are operationally safe, effective, and reliable for ground and flight 
operations

[[Page 1624]]

including: Taxi, takeoff, climb, cruise, descent, approach, landing, 
roll-out, or missed approach as applicable, and, (2) if visual 
reference requirements apply, the pilot is able to determine that 
flight visibility is adequate for safe takeoff or landing.'' The 
commenter stated that realization of EVS benefits and other 
significant, technology driven, operational and safety enhancements are 
dependent on structuring language within the NPRM that encourages 
further technological development and does not specifically limit 
system design. It is important to avoid rulemaking language that 
narrowly defines systems or technologies, but instead addresses 
fundamental requirements. The commenter believed that approval of EVS 
or other systems should be based on demonstrating equivalent levels of 
safety and performance to that of currently approved instrument 
approach and landing systems.
    FAA's response: The FAA disagrees with the commenter and believes 
that the regulatory language proposed by the commenter is too open-
ended and non-specific to be applied as a rule. This final rule will 
allow an aircraft to be operated to lower altitudes (DH or MDA) than 
presently permitted for straight-in instrument approach procedures 
other than Category II or Category III if the conditions of the 
proposed language are met. Thus, this final rule provides an 
operational benefit (operations to lower altitudes in marginal weather) 
for those who equip their aircraft with this new technology and who 
meet the other conditions of the new rule. In addition, many of the 
commenters' proposed uses of an EFVS are beyond the scope of this 
rulemaking because the FAA did not propose to allow the use of EFVS to 
meet any other regulatory requirements. However, the proposed 
rulemaking does not impose restrictions on other voluntary uses of an 
FAA certified EFVS where the pilot is not using the EFVS to meet a 
regulatory requirement, i.e., situational awareness.
    The FAA does not intend to discourage technical innovation, and 
this rule does nothing to hinder innovation. Instead, this rule 
provides a way for a new technology that has been developed, tested, 
and certified by the FAA to be used in a way that provides operational 
and safety benefits. The rule provides an acceptable alternative to the 
previously existing requirements for flight visibility and allows 
operations below the DH or MDA without affecting the standard 
instrument procedures or the prescribed visibility minima. Without the 
use of EFVS, it would not be possible to offer these significant 
operational benefits. The operational concepts for using other 
innovative technology may differ from that underlying this rule.

IV.9. Other Technologies

    Comment: Several commenters stated that the NPRM excluded the use 
of other types of technology that can achieve the same results as EFVS, 
and that the NPRM would discourage technology and innovation by 
precluding or seriously discouraging the use of other technologies such 
as synthetic vision systems (SVS). Another commenter noted several 
potential advantages of an SVS over an EFVS. EFVS unpredictably has a 
limited vision capability while SVS capability would be reliably 
available for much farther distances (such as full scene capability 
from the final approach fix), allowing for improved approach stability 
and lower crew workloads.
    A commenter noted that an EVS is currently using a raster 
(television) display technology, while SVS can be implemented in 
``Stroke'' (line drawing) technology. Raster inherently obscures the 
entire view of the outside world through the HUD while Stroke has no 
obscuration at all except where the actual relevant material, such as 
runway outlines, are being displayed. The FAA/USAF Synthetic Vision 
Technology Demonstration Program documented instances where the crew 
using HUD EVS were unable to see real visual cues due to the EVS raster 
obscuration of the visual runway view, forcing unnecessary go-arounds.
    This commenter also stated that EVS images in minimal weather will 
be limited to ``improved eyesight'' giving only a few runway lights. An 
SVS-enhanced solution would give complete approach lead-in, as well as 
outline of the load bearing boundaries of the runway.
    This commenter believed that at most runways in wet, icy, or snowy 
weather, EVS is unpredictably incapable of providing any indication of 
where the desired touchdown point is on the runway or the extent of the 
touchdown zone (typically extending from 500 feet to 3,000 feet down 
the runway). SVS technology would be able to reliably provide both.
    FAA's response: The FAA acknowledges that a synthetic vision system 
could have certain display advantages in comparison to EFVS with 
respect to information content and method of presentation and does not 
intend to prohibit future implementation of standard SVS instrument 
approach procedures. However, the proposed rule was intended to provide 
an analogous alternative to Sec.  91.175(c)(2) (flight visibility) for 
descent and operation below DH or MDA, to conduct straight-in 
instrument approaches, other than Category II or Category III, with 
standard minima. The key difference between SVS and EFVS is that an 
EFVS provides an independent real-time view for the pilot. Whereas, an 
SVS is comprised, in part, of a database component, a precise 
navigation component, instrument data interfaces and a processing 
component that would compute and ``draw'' the forward view based on 
what the external view should be if the data base and navigation 
components are valid. The database-derived SVS display is not a real-
time source of forward scene information as is the EFVS sensor-based 
image. Although an SVS may display a synthetic view of the runway, it 
is incapable of displaying a real-time view of the external scene and 
the pilot would not be able to determine if the runway were 
contaminated by water, ice, or snow. Therefore, an SVS display cannot 
serve as an alternative means of complying with Sec.  91.175(l)(3) for 
descending below DH or MDA.

IV.10. Regulatory Bar To Use of Systems Such as SVS

    Comment: One commenter stated there is no regulatory bar to use of 
systems such as SVS. In fact, systems having the characteristics of SVS 
were also developed and implemented for use in the 1960s and 1970s. 
Specific U.S. civil examples are available. Further, according to the 
commenter, the NPRM provided no technically sound basis to justifiably 
and inherently discriminate between the merits of SVS, EVS, and other 
systems for certain specific low-visibility related tasks or 
applications.
    FAA's response: An SVS cannot provide enhanced flight visibility, 
especially the capability to show a real-time image of an aircraft or 
vehicle on the runway of intended landing. Although an SVS has been 
approved for flying an instrument approach procedure, it has not been 
approved for operations below the authorized DH or MDA. Therefore, an 
SVS cannot be used below the DH or MDA unless the flight visibility is 
not less than the visibility prescribed in the standard instrument 
approach procedure being used (Sec.  91.175(c)(2) and unless at least 
one of the items in Sec.  91.175(c)(3) is distinguishable. Operations 
below the DH or MDA are only authorized if the requirements of Sec.  
91.175 (c)(2) and (c)(3) are met or the requirements of Sec.  
91.175(l)(2) and (l)(3) are met. There is a bar to using an SVS to fly 
a standard

[[Page 1625]]

instrument approach procedure and descend below the authorized minima 
(DH or MDA) without having the required flight visibility or enhanced 
flight visibility. There is also a bar to using an SVS, even above the 
DH or MDA, unless the FAA has specifically approved the operation.

IV.11. Differentiation Between Runway and Taxiway

    Comment: A commenter stated that the NPRM would not have required 
that a capability exist to differentiate a taxiway or other runway 
similar environment (e.g., lighted highway or drag-strip) from a runway 
environment. EVS systems are usually incapable of distinguishing 
taxiway lighting or even taxiway environments from runway environments, 
especially when considering nonprecision runways. Examples of these 
difficulties include that the sensor cannot determine the visual color 
of the lighting system, and for imaging radar-based systems, the 
radiated heat pattern is different than the visual light distribution 
(taxiway lights do not project light upwards at the same angle as 
runway lights). To mitigate this problem, the pilot must see the runway 
visually at 100 feet above the touchdown zone elevation to land the 
aircraft.
    FAA's response: The FAA acknowledges that some enhanced flight 
visibility systems may not work as well as others to adequately portray 
the forward scene and the visual references listed in the rule. During 
certification of the EFVS installation, the applicant must demonstrate 
that pilots will be able to use the EFVS to distinctly see and identify 
these visual references and determine whether the enhanced flight 
visibility is no less than the prescribed minimum. The EFVS will be 
tested in a variety of environmental conditions and at several 
different runways. The FAA will not approve a system that is found to 
be prone to misidentification of the listed visual references or in 
other ways does not perform its intended function.
    The FAA believes it is not necessary to explicitly require the EFVS 
to distinguish runways from taxiways. However, the rule does list 
specific visual references of an approach light system or a runway and 
touchdown zone that would distinguish a runway from other features of 
the airport environment, at least one of which must be distinctly 
visible and identifiable using the EFVS and the rule requires that the 
touchdown zone be distinctly visible and identifiable to the pilot. By 
meeting these requirements, the pilot can know that the aircraft is 
approaching the desired runway, and not a taxiway. If a runway feature 
and a touchdown zone feature cannot be distinguished from a taxiway 
feature, then the runway is not distinctly visible and identifiable.
    The rule provides for a safe operation, because the pilot must 
execute a missed approach if at any time between the DH or MDA and 100 
feet above the touchdown zone elevation the visual references are not 
distinctly visible and identifiable by using the EFVS. Furthermore, 
upon reaching 100 feet above the touchdown zone elevation, the pilot 
must be able to see and identify, without reliance on EFVS, the 
threshold (lights or markings) or touchdown zone (lights or markings) 
of the intended runway. If at 100 feet above the touchdown zone 
elevation, the pilot cannot see the threshold (lights or markings) or 
the touchdown zone (lights or markings), the pilot must execute a 
missed approach.

IV.12. Obstacle Clearance

    Comment: One commenter stated that giving obstacle avoidance credit 
to EFVS is incorrect. Many nonprecision approaches are constructed such 
that the MDA and visibility charted provide the crew with the 
capability to see and avoid obstacles or obstructions in the possible 
paths descending from the MDA or from the terminating point of the 
approach.
    This commenter asserted that allowing EFVS to be used in lieu of 
charted flight visibility may put the aircraft at serious risk, since 
many obstructions or obstacles are not visible to EVS sensors and thus 
would not be displayed to a crew relying on an EFVS to transit the area 
below the MDA and 100 feet above the touchdown zone elevation. Worse, 
according to the commenter, is the ability of EVS to see many types of 
natural or cultural features is generally unpredictable due to thermal 
characteristics.
    FAA's response: The FAA agrees with the commenter that some EFVSs 
may not be able to consistently detect obstacles in the visual segment 
of an instrument approach procedure under certain conditions. Many of 
the obstacles the commenter refers to would not be a problem if the 
pilot complies with the same three requirements as Sec.  91.175 (c) for 
a pilot to descend from the MDA on a nonprecision approach. The three 
requirements applicable to Sec.  91.175 (c) and (l) are: (1) Pilot must 
observe that the enhanced flight visibility (or flight visibility) is 
not less than the visibility specified for the procedure; (2) at least 
one of the specifically listed visual references must be distinctly 
visible and; (3) the aircraft must continuously be in a position from 
which a descent to a landing on the intended runway can be made at a 
normal rate of descent using normal maneuvers.
    If a pilot meets all of the requirements of Sec.  91.175 (l), the 
pilot should have adequate visibility to see the runway environment. In 
addition, while an EFVS may not detect all of the obstacles the 
commenter refers to, an EFVS may reveal some of them. For example, 
there may be cues observable in the EFVS display that would indicate 
that an obstacle exists, other than a distinct image of an obstacle. 
For example, a partial obstruction of the runway may indicate terrain 
between the aircraft and the runway.
    The FAA acknowledges a key point made by the commenter, that it is 
uncertain that the EFVS will always enable the pilot to detect all 
obstacles in the visual segment of the approach. A similar risk is 
present today because it is also uncertain that pilots will always be 
able to detect obstacles visually when operating conventionally under 
Sec.  91.175 (c). Adverse visual conditions, such as low contrast, 
shadows, snow cover (especially coupled with falling snow and/or 
overcast conditions, i.e., ``whiteout''), and situations of similar 
obstacle and background coloring can occur even when flight visibility 
and the other requirements for descent below MDA are satisfied.
    The risk for a nonprecision approach using EFVS is significantly 
mitigated by the rule by only permitting reliance on an EFVS to 
straight-in approaches. The FAA believes it is unlikely that a pilot 
following straight-in instrument approach procedures will encounter an 
object in the flight path. The FAA does acknowledge that it is possible 
for an EFVS to not detect obstacles in the visual segment of an 
approach even if the pilot has the required enhanced flight visibility. 
However, the FAA believes that obstacle clearance can be maintained, if 
the pilot uses the recommended procedures below to fly a straight-in 
instrument approach procedure with a MDA, and uses the flight path 
vector and flight path angle reference cue displayed by the EFVS to 
monitor and maintain the desired vertical path and begins descent below 
the MDA:
    (1) At the VDP, if charted, or a reasonably calculated visual 
descent point; or
    (2) Using the descent angle published on the instrument approach 
procedure or if a descent angle is not published, a descent angle as 
high as suitable for that type of aircraft.

[[Page 1626]]

    To clarify the FAA's intent as to which topographical features that 
an EFVS must detect and display, the FAA is amending proposed Sec.  
91.175 (m)(1) to state that an EFVS must be able to display 
topographical features of the airport environment. It is not the FAA's 
intent to require an EFVS to detect all obstacles while transiting the 
visual portion of the final approach segment.

IV.13. Weather-Related Comments

    Comment: One commenter recommended that the FAA modify Sec.  
135.225 (b) and associated paragraphs to accommodate authorized 
operators using EFVS by allowing an approach to be initiated if 
reported weather minimums are lower than the minimums established for a 
specific EFVS. The commenter stated that reported visibility, measured 
by a transmissometer, is not a reliable indicator of EFVS performance 
at or below DH or MDA because it does not measure visibility in the 
same part of the electromagnetic spectrum as the EFVS. The commenter 
stated that this recommendation would increase the probability of a 
successful landing with operational and safety benefits.
    FAA's Response: The FAA disagrees that modifying the reported 
visibility requirement for commencing the approach would increase 
safety. While the FAA agrees that the transmissometer does not operate 
in the same portion of the electromagnetic spectrum as the EFVS, its 
measurements are just as representative of the visibility conditions 
at/below 100 feet height above touchdown zone elevation as they are 
today. Even today, in conventional approaches, the reported visibility 
is not a totally reliable indicator of flight visibility at the DH or 
MDA, but is more representative close to the runway, where the pilot 
must use the visual references to complete the manual landing. This 
commenter's recommendations are outside the scope of the NPRM.

IV.14. Equipment-Related Weather Minimums

    Comment: A commenter stated that the altitude criterion for EFVS is 
not based on the capability of the equipment and that specifying an 
absolute altitude as a minimum altitude for EFVS usage during approach 
and landing inhibits the incentive to advance optics technology to a 
level at which weather obscurations will be transparent to the EFVS. 
The commenter stated that by providing latitude for EFVS minimum 
altitude usage, the FAA could preclude additional changes to the 
regulation in the future or the need for imposing special conditions on 
equipment certification.
    This commenter recommended that the minimum altitude for operation 
with an EFVS be predicated on the specific equipment installed and 
certified by the FAA (or approved by the FAA for foreign registered 
aircraft). The commenter proposed that the FAA change to Sec.  
91.175(l)(4) to say: ``At and below the minimum altitude at which the 
EFVS was certified or approved by the FAA, the * * *.''
    Another commenter stated that once the performance limit for a 
particular EFVS is reached, the use of that particular EFVS is no 
longer approved for landing credits, and the requirements of Sec.  
91.175(c)(3) become applicable. As a result, Sec.  91.175(l)(4) is no 
longer necessary.
    FAA's response: The FAA disagrees with the commenter's premise that 
the transition to outside visual references at 100 feet above the 
touchdown zone elevation is an altitude criterion for EFVS. The rule 
does not establish an altitude criterion for use of EFVS, per se, nor 
does it establish a minimum use height, in the same sense that such 
limitations are placed on autopilots, for example. The purpose of the 
rule is to apply the same DH or MDA and visibility minima prescribed in 
the standard instrument approach procedure when EFVS is used (i.e., 
EFVS does not reduce the minima), so it would be inconsistent to base 
an altitude criterion on the capability of a particular EFVS.
    The FAA also disagrees with the comment that the rule establishes a 
performance limit for EFVS. Section 91.175(l)(4) requires that the 
pilot transition to the actual outside view by 100 feet above the 
touchdown zone elevation. The requirement is based on the operational 
need for the pilot to obtain visual contact (through the window) with 
the runway features to land, and is consistent with the time-tested 
operational concept of Sec.  91.175(c)(3)(i). Section 91.175(l)(4) is 
necessary because it identifies the requirement for pilots using EFVS 
to make the transition to outside references by 100 feet above the 
touchdown zone elevation. While the commenter is correct that the 
references listed in (l)(4) are similar to those in listed in (c)(3), 
the focus of (l)(4) is on the transition to outside visual references 
that are especially needed for the manual landing (e.g., runway 
threshold and touchdown zone).
    The FAA recognizes that some enhanced flight vision systems may 
perform better than others. If, during certification, an EFVS is not 
found safe to use down to 100 feet above the touchdown zone elevation, 
then it will not be approved because it cannot perform its intended 
function.

IV.15. Operational Intent of the Rule

    Comment: One commenter stated that in normal IFR operations, 
current Sec.  91.175 requires that the pilot have clear and 
unobstructed visibility of the approach lights to continue below the DH 
or MDA. The NPRM seeks to augment the visibility requirement by 
permitting the use of a sensor-based imaging device in conjunction with 
a HUD to enhance the pilot's visibility down to the 100-foot level, at 
which altitude the existing visibility requirements of Sec.  91.175 
again become the operant rule, and the pilot must make the decision 
whether to go around or to land the airplane based on unassisted visual 
references only (not based on the EFVS imagery). According to this 
commenter, the proposed rule would apply primarily to ``fly down and 
take a look'' approach operations. In order to avoid controversy in 
application of the proposed rule, this commenter recommends that the 
FAA clarify the operational intent of the proposal, to include specific 
visibility.
    FAA's response: The rule does not augment the visibility 
requirements of Sec.  91.175(c), but instead provides an alternative 
requirement (e.g., enhanced flight visibility) for operation below the 
DH or MDA. The use of EFVS does not alter the visibility requirements 
for commencing the approach. Today, part 121, 125, and 135 operators 
may not initiate an instrument approach procedure (Sec.  121.651(b), 
Sec.  125.381(b), or Sec.  135.225(b)) unless the reported visibility 
is equal to or more than the visibility minimums prescribed for that 
procedure. This requirement does not exist for part 91 operators, which 
implies that they may commence the approach when reported visibility is 
below minimums. In addition, EFVS does not affect the visibility or 
systems and pilot qualification requirements for Category II/III 
operations. By 100 feet above the touchdown zone elevation, the pilot 
must be able to see and identify visual references without reliance on 
EFVS. While use of EFVS during Category II and III operations may be 
permissible, such use must be specifically authorized as part of the 
operator's authorization for Category II and III approaches either by 
operations specifications for part 121, 125, or 135 operations or per 
Sec.  91.189.

[[Page 1627]]

IV.16. Operational Benefits for Part 121, Part 125, and Part 135 
Operations

    Comment: Several commenters stated that there should not be any 
difference between part 91 and parts 121, 125, and 135 with respect to 
the requirements for commencing the approach with EFVS. Several 
commenters recommended that pilots operating under parts 121, 125, and 
135 should be able to begin the approach based on having an EFVS 
regardless of the reported weather.
    Another commenter proposed that, for part 121 and part 135, 
operations equipped with a certified EFVS be allowed to initiate the 
approach in weather conditions reported as low as 1,200 feet RVR or \1/
4\ mile visibility.
    Another commenter recommended deleting Sec.  121.651(b) 
(requirements for commencing an approach) if the operator has a 
certified EFVS.
    FAA's response: The FAA disagrees. The commenters' recommendations 
are outside the scope of the NPRM and would not provide for an adequate 
level of safety for operations conducted for compensation or hire for 
the following reasons. The proposal would undermine the current safety 
standards of not permitting a pilot to begin an instrument approach 
procedure if current weather reports are not available for the 
procedure or they report a below-authorized weather condition for 
operations conducted under parts 121, 125, or 135. These weather 
reports provide necessary safety information to pilots in addition to 
visibility information.

IV.17. Part 121, Part 135, and Part 129 Operations

    Comment: One commenter stated that extending the NPRM text to parts 
121, 135, and 129 would be potentially unsafe as written (e.g., systems 
strictly meeting this rule could nonetheless lead pilots and aircraft 
into unsafe conditions), and are as yet operationally unsupported and 
unjustified. It would be most inappropriate to include specific EVS 
provisions in parts 121, 135, and 129 in the proposal at this time. 
Operational utility and safety of operations as implied by the NPRM, as 
well as legitimate ``proof of concept,'' are far from established at 
this point.
    The commenter stated that part 129 operators, JAA, and other 
European representatives recently expressed concerns about such 
operations, particularly considering that those EVS operations are more 
appropriately termed Category II or III, than Category I.
    FAA's response: The FAA disagrees that part 121, part 129, and part 
135 operators cannot operate safely under this rule. This rule 
parallels the well-tested safe approach procedures of Sec.  91.175(c). 
The commenter did not identify how these operations will be unsafe. The 
FAA did not receive any response from the JAA or European 
representatives regarding this rule.

IV.18. Operational Experience Before Credit for Lower Minimums

    Comment: A commenter stated that, as with any new aircraft system, 
EFVS operational experience must be documented prior to further 
consideration for EFVS credit for lower minimums. Any EFVS operational 
limitation should be documented within the operator's AFM supplement.
    FAA's response: The FAA does not believe that operational 
experience is necessary for an approved EFVS used in accordance with 
the rule because this rule does not provide for the use of EFVS to 
obtain credit for lower minima. The FAA agrees that any EFVS operating 
limitations found during certification should be stated in the AFM/RFM 
supplement.

IV.19. Takeoff Minimums for EFVS

    Comment: Several commenters stated that proposed Sec. Sec.  91.175, 
121.651, 125.381, and 135.225 make no provisions for the enhanced 
vision flight vision system to be used to meet takeoff visibility 
requirements. Given that the system can be used to meet flight 
visibility requirements during approach, it follows that some credit 
should be able to be derived for takeoff operations below the 
established takeoff visibility.
    FAA's response: The use of EFVS to meet takeoff visibility is 
beyond the scope of this rulemaking. This rule applies only to approach 
to straight-in landing operations below DH or MDA using an EFVS. The 
FAA did not propose the use of EFVS during takeoff.

IV.20. Rule Should Be an Advisory Circular (AC)

    Comment: Several commenters asked why the FAA proceeded by 
rulemaking action instead of by AC. One commenter also stated that the 
NPRM could inappropriately set a precedent that rulemaking is required 
to implement new technology when rulemaking is not required.
    FAA's response: The FAA is proceeding by rule instead of AC because 
this rule permits the use of new technology for straight-in approach 
landings by in essence creating an exception to the existing regulatory 
prohibitions in Sec.  91.175(c)(2). An agency is required to conduct 
rulemaking when it considers changing an existing policy limitation in 
the rules. In this case, if an EFVS is approved by the FAA, meets all 
the requirements of Sec.  91.175(m) and is determined to provide an 
equivalent level of safety, this operational rule will provide an 
alternative to the flight visibility requirement of Sec.  91.175(c)(2) 
and allow the operator to descend below the DH or MDA if the 
requirements of Sec.  91.175(l)(2) and (l)(3) are met.

IV.21. Terminology: Category I and Advisory Circulars

    Comment: Several commenters stated that in accordance with the 
recently published AC 120-29A, ``Criteria for Approval of Category I 
and Category II Weather Minima for Approach,'' dated August 12, 2002, 
terminology for approach categories have been changed. A Category I 
approach is any approach that has a DH of not less than 200 feet AGL 
and a visibility requirement of not less than \1/2\ statute mile. The 
reference to precision and nonprecision approaches is no longer 
applicable and the terminology has been redefined. These commenters 
believed that conforming to a common terminology, as presented in AC 
120-29A, provides additional clarity in the regulation.
    FAA Response: The FAA disagrees with the comment that the NPRM was 
not consistent with the intent and direction of AC 120-29A. That 
advisory circular discusses the terms for Category I approaches which 
includes nonprecision approaches, more specifically, an approach 
without vertical guidance. Although this definition for a Category I 
approach has been more commonly used in operations specifications for 
part 121, part 125, part 129 and part 135 operators, the FAA wants to 
make it clear that an EFVS could be used with a nonprecision approach 
for operators not using operations specifications.
    AC 120-29A also mentions the generic term ``enhanced vision 
system'' (EVS). While this rule does not preclude the limited use of 
EFVS as described in AC 120-29A, it does permit an approved EFVS to be 
used to determine ``enhanced flight visibility'' which is a significant 
additional benefit for operators who were limited to using EFVS for the 
purposes described in the AC.

IV.22. Coordination Through TAOARC and AWO Process

    Comment: Some commenters stated that the NPRM should not be issued 
in its current form and any subsequent revisions to the NPRM should be 
coordinated through both the All-Weather Operations (AWO)

[[Page 1628]]

harmonization process and the FAA TAOARC processes and be consistent 
with other related NPRMs (e.g., RNAV, Docket No. FAA-2002-14002, and 
Special Operating Rules for the Conduct of Instrument Flight Rules 
(IFR) Area Navigation Systems (RNAV) in Alaska, Docket No. FAA-2003-
14305).
    FAA's response: The comments about the proposed changes in 
terminology for approach categories in the RNAV NPRM (Docket No. FAA-
2002-14002) are not within the scope of the notice for this rulemaking 
and are not incorporated into this final rule. The Alaska Special 
Federal Aviation Regulation (SFAR) only addressed en route requirements 
for RNAV equipment and training and did not address RNAV instrument 
approach procedures.
    The FAA disagrees with the comment that the current wording, 
especially definitions, of the NPRM and any subsequent revisions to the 
NPRM proposals should be coordinated through both the AWO harmonization 
and FAA TAOARC processes, and be consistent with the other noted NPRMs. 
This final rule action does not preclude persons from submitting 
recommendations concerning EFVS through their representatives on the 
AWO working group.

IV.23. EFVS Flight Path Performance

    Comment: One commenter stated that the proposed requirements of the 
NPRM pose safety concerns. According to the commenter, representatives 
of European authorities, and others, correctly identify that some of 
the proposed operations with the above systems are, and should be 
appropriately classified and recognized as, Category II and Category 
III operations. Yet the proposed EFVS do not appear to come close to 
meeting the path performance standards necessary for safety for such 
operations. (See AC 120-28D, ``Criteria for Approval of Category III 
Weather Minima for Takeoff, Landing, and Rollout.'') The NPRM cited no 
evidence that adequate flight path performance can be demonstrated with 
imaging systems alone, whether TV, imaging radar (IR), or radar based. 
The commenter stated that current operating history with such systems 
in research and development programs and military operations indicates 
the opposite conclusion, which is why such operations often rely on use 
of autoland. Further, this commenter believed, there is no evidence 
presented in the NPRM that the ``aircraft state or guidance elements'' 
cited can perform to the levels necessary for either Category II or 
III, and particularly not for operations below 100 feet height above 
touchdown (HAT), flare, and rollout, or for missed approach, where such 
EVS systems are likely to lead a pilot without guidance assistance.
    FAA's response: The FAA disagrees. The FAA believes the commenter 
misunderstood the purpose and applicability of the NPRM regarding the 
use of EFVS in the conduct of instrument approach procedures. This rule 
does not permit an operator to rely on an EFVS for category II or 
category III type approaches when an EFVS is relied upon for enhanced 
flight visibility pursuant to Sec.  91.175(l). Use of the EFVS is an 
alternative means to comply with flight visibility requirements. To 
clarify any misunderstandings concerning the applicability of this 
rule, the FAA is adding language in the text of the rule in Sec.  
91.175(l)(1) to limit the application of this rule to straight-in 
instrument approach procedures other than category II and category III 
operations. Advisory Circular 120-28D and AC 120-29A both provide 
guidance for the criteria for approval of weather minima (Category I, 
II, III) and the use of enhanced vision systems (EVS). The guidance 
provided in the ACs describe the functionality of EVS to ensure the 
accuracy or integrity of other flight guidance or control systems in 
use during Category I, II, or III operations. The proposals in the NPRM 
described a new kind of functionality for EVS/EFVS.
    EFVS can be used to enable pilots to determine ``enhanced flight 
visibility'' in lieu of ``flight visibility.'' Whether EFVS approved 
for determining ``enhanced flight visibility'' can also be approved for 
ensuring the accuracy or integrity of other flight guidance or control 
systems will depend upon whether the candidate system can be 
demonstrated to be acceptable to the FAA in a proof of concept 
evaluation as well as meeting the approval criteria in AC 120-28D or AC 
120-29A.

IV.24. Inconsistency With Terminology in AC 120.28D or AC 120.29A

    Comment: One commenter stated that the NPRM terminology presented 
an inappropriate use and meaning of Category I. Since the 1980s in 
operations specifications, and since 1999 in FAA criteria, this use of 
Category I terminology is incorrect and inappropriate. Since the 1980s, 
Category I applies not only to United States ILS, GLS, and other 
instrument approaches in operations specifications, but since 1999 has 
been additionally recognized in other appropriate FAA advisory circular 
criteria. Hence, the use of Category I and II terminology in the NPRM 
is incorrect and inappropriate and should be withdrawn. Accordingly, 
Category I, II and III definitions should be retained for U.S. use as 
currently described in FAA ACs 120-29A and 120-28D, and current 
operations specifications. If and when ICAO definitions for Category I, 
II, and III are updated through FAA/JAA AWO or other harmonization 
activities, or otherwise agreed in ICAO, the United States should 
consider further amendments of these terms. Hence, these provisions are 
much too technology-specific, misleading, and potentially unsafe as 
written (e.g., systems strictly meeting this rule could nonetheless 
lead pilots and aircraft into unsafe Category II and III conditions) 
and are operationally unsupported and unjustified. Other commenters 
made similar statements.
    FAA's response: The FAA disagrees with this comment for the reasons 
discussed in the response to the EFVS flight path performance comment. 
(See ``IV.23. EFVS flight path performance'' above.) In addition, the 
FAA disagrees that this final rule will potentially result in unsafe 
operations as written. The FAA believes that the use of EFVS will 
result in an equivalent level of safety for those operators who choose 
to equip their aircraft with that equipment. As with any aircraft 
system, to ensure the safety of operations in which EFVS is used, the 
operator must comply with the operating limitations specified in the 
Airplane or Rotorcraft Flight Manual and, for commercial operators, any 
conditions and limitations regarding its use are specified in the 
operator's operations specifications.
    The rule will not lead pilots and aircraft into unsafe Category II 
or Category III conditions. The safety of the EFVS concept of 
operations, unlike the concept for Category II or Category III 
operations (e.g., higher integrity, more rigorous guidance and 
navigation accuracy to achieve lower minima), is that EFVS provides an 
alternate means to satisfy the visibility requirements without reducing 
the visibility minima. The rule, following an operational concept 
analogous to that of Sec.  91.175(c), requires the pilot to meet the 
prescribed visibility minima, based on ``enhanced flight visibility'' 
in lieu of ``flight visibility;'' to distinctly see and identify either 
(1) the runway threshold and the touchdown zone, or (2) the approach 
light system; and, by 100 feet above touchdown elevation to see the 
runway references needed for a manual landing without reliance on EFVS. 
Further, the rule does not relieve commercial operators from the 
visibility requirements for commencing the

[[Page 1629]]

approach. Based on these facts and the clarifying language added to 
Sec.  91.175(l)(1), the FAA does not believe the rule will mislead a 
pilot into unsafe conditions.

IV.25. EFVS Use for Category II & Category III Approaches

    Comment: Several commenters recommended that EFVS be used for 
Category II and III approaches, which the proposed rule did not seem to 
permit. The EFVS use should be permitted for situational awareness and 
for visual approach conditions as well as for Category I, II, and III 
approach conditions. This should apply to autoland and to hand-flown 
approaches.
    Commenters recommended that the FAA:
    [sbull] Clarify the intended usage of a certified EFVS during a 
Category II or III approach.
    [sbull] Allow the EFVS to be operated during a Category II or III 
approach.
    [sbull] Clarify what is meant by ``the stringent reliability, 
redundancy and other criteria that would be applicable for use of EFVS 
for Category II and III approaches'' as stated in the EFVS NPRM.
    Another commenter proposed that the rule state: ``Any approach 
using EFVS will de facto be equivalent to a CAT2+ type of approach, as 
there is no more flight visibility requirements and EFVS can be used 
down to 100 ft.'' The commenter stated that in order to be consistent 
with current rules and to ensure a correct level of safety, approaches 
conducted with EFVS systems should offer a sufficient safety level and 
architecture compatible with current Category II rules. The commenter 
stated that EFVS software design assurance levels should be the same as 
for equipment used to support Category II and Category III operations. 
Therefore, the commenter stated, EFVS-based operations should require 
that: (1) The aircraft is equipped with at least 2 DO-178B Level B 
qualified ILS receivers, with comparison monitors; (2) ILS or MLS 
ground transmitters used during an EFVS approach should comply with 
Category II safety level; and (3) EFVS sensor imaging process should 
ensure that no picture lockup can happen. EFVS sensor image processing 
software should be at least DO-178B level C qualified.
    FAA's response: The final rule does not permit an operator to rely 
on an EFVS for Category II and III approach procedures, and the final 
rule does not change the requirements for Category II and III 
operations. Any future proposed use of EFVS for Category II and III 
operations must comply with current regulatory requirements found in 
Sec. Sec.  61.67 and 61.68, 91.189 through 91.193, 121.651(d)(3), 
121.567, 125.325 or 135.78 that Category II and Category III operations 
must be authorized by the Administrator. Advisory Circulars AC 120.29A 
and AC 120.28D provide guidance concerning the stringent reliability, 
redundancy and other criteria for equipment used in Category II and 
Category III operations.
    Proposed revisions to Sec.  91.175(l) do not have provisions for 
Category II and III operations because that section only applies to 
straight-in approach operations, i.e., approaches with a DH or MDA no 
less than 200 feet HAT. The NPRM did not intend to unconditionally 
prohibit the use of EFVS during Category II and Category III 
approaches. If EFVS is used during Category II or Category III 
operations, it is only in addition to the other required equipment, 
procedures, crew qualifications and so on, provided that the EFVS does 
not interfere or degrade the low visibility operation. The requirements 
and criteria for the equipment, procedures, training, maintenance, and 
airport features to be used for Category II and Category III approaches 
are well established and must still be complied with, regardless of 
EFVS. The use of EFVS in Category II or III operations, unlike its use 
for operations under Sec.  91.175(l), does not result in operational 
credit (e.g., a pilot using an EFVS on a Category II or III operation 
cannot fly lower than a pilot not using an EFVS in a Category II or III 
operation.)
    The operational approval that permits an operator to conduct 
Category II and/or Category III approach operations must include 
specific provisions for the use of EFVS during such operations. EFVS 
must first be demonstrated to be suitable during such operations. 
Airborne systems used for Category II and III operations were first 
certified to comply with airworthiness criteria found in AC 120-28D or 
AC 120-29A, as applicable. EFVS changes the installed configuration of 
those airborne systems, and there should be airworthiness 
demonstrations to show that the new system configuration still complies 
with the applicable criteria. The FAA anticipates that there will be 
visibility conditions where ``flight visibility,'' but not ``enhanced 
flight visibility,'' is lower than the prescribed approach minima. It 
is important to recognize the differences between a Category II 
approach and an instrument approach using an EFVS under Sec.  
91.175(l), even when flown in such conditions. Category II approaches 
require a runway facility that satisfies the Type II criteria found in 
ICAO Annex 10. The Category II instrument approach procedure specifies 
decision height and visibility minima that are less than for a Category 
I ILS approach to the same runway. The airborne equipment must meet 
specific performance and integrity criteria outlined in AC120-29A and 
its Appendix 3.
    Essentially, Category II and Category III operations depend on 
improved flight path performance and integrity as mitigation for lower 
visibility conditions. Instrument approach procedures other than 
Category II or Category III that are based on compliance with Sec.  
91.175 (l) and (m), use EFVS as an alternative means that would allow 
the use of an EFVS to determine enhanced flight visibility and would 
permit the descent and operation below the DH. The Category I ILS 
instrument approach procedure, which specifies a decision height and 
minimum visibility, is not changed when using EFVS in compliance with 
the rule change proposed in the NPRM. Essentially, the rule permits 
descent based on ``enhanced flight visibility'' rather than ``flight 
visibility'' being no less than the visibility prescribed in the 
instrument approach procedure. The FAA disagrees that an approach using 
EFVS is the de facto equivalent of a Category II or Category III 
approach.
    Advisory Circular guidance for certification of EFVS, and perhaps 
even a technical standard order (TSO), might be issued in future. In 
the mean time, issue papers and special conditions may be used to 
certify EFVS based on its ability to perform its intended function and 
the required characteristics as specified in the rule, a system safety 
assessment, and existing certification criteria for software, 
programmed logic devices, head-up displays, and other criteria, as 
applicable to the EFVS design. In addition to criteria contained in 
issue papers from previous certifications, industry documents, such as 
Society of Automotive Engineers (SAE) Aerospace Standard (AS) 8055 and 
Aerospace Recommended Practices (ARP) 5288, provide a useful starting 
point for guidance material.
    The FAA will consider the commenter's proposed minimum software 
design assurance level A for certain EFVS functions during the 
certification process. The FAA requires a system safety analysis, 
including a functional hazard assessment that will provide a basis for 
the design assurance levels of software-based functions, in accordance 
with well-established certification processes. As many commenters 
stated, part 91 is not the

[[Page 1630]]

place for certification requirements. The FAA limits its list of 
required features and characteristics of EFVS in Sec.  91.175 (m) to 
the minimum needed to satisfy operational requirements.

IV.26. Compliance With Sec.  91.1039

    Comment: A commenter states that it has a strong interest in the 
NPRM's applicability to Sec.  91.1039 IFR takeoff, approach, and 
landing minimums, under ``Subpart K--Fractional Ownership Operations'' 
as proposed on July 18, 2001 (66 FR 37520). This commenter believed 
that the community regulated under that proposed subpart K would 
achieve significant safety benefits and operational efficiencies given 
access to the full use of EFVS.
    FAA's response: The FAA agrees. The amendment to Sec.  91.175 
applies to operators conducting operations under part 91 subpart K (see 
final rule at 68 FR 54568). The requirements in Sec.  91.1039 will 
supplement those in Sec.  91.175.

IV.27. Definitions--Italics and Capitalization

    Comment: One commenter requested clarification of the italics and 
capitalization in the definition of EFVS.
    FAA's response: The definition of EFVS contains no italics or 
capitalization, except for the title. The title was italicized in the 
same format as all part 1 definitions.

IV.28. Definitions--Scope of Enhanced Flight Vision Systems

    Comment: One commenter recommended broadening the definition of 
EFVS and stated the definition of enhanced flight visibility is 
unjustified and inappropriate. Also, the commenter said that it 
unfairly targets or favors one technology and without more operating 
experience could be unsafe.
    FAA's response: The FAA disagrees with this comment because the 
intent of this rule is to provide a basis for the use of imaging sensor 
technologies that can provide a real time display of the external 
scene. The FAA will ensure the safety of an EFVS system during the 
certification process.

IV.29. Definitions--Examples of Enhanced Flight Vision Systems

    Comment: A commenter recommended deleting examples of EFVS 
technology listed in the definition of EFVS, because including those 
examples would inhibit the development of new technologies due to a 
lack of regulation and future certification guidelines.
    FAA's response: The FAA disagrees with this comment. Simply listing 
examples of current EFVS technology in the definition of EFVS does not 
preclude the use of other EFVS technologies.

IV.30. Definitions--Enhanced Vision Systems

    Comment: Several commenters suggested using the term enhanced 
vision system (EVS) instead of EFVS because EVS is an industry-
recognized term.
    FAA's response: The FAA considered the terminology to be used for 
EFVS, including alternatives such as the commonly used ``enhanced 
vision system.'' There are a variety of systems labeled EVS and a 
number of EVS definitions which the FAA believes could be confused with 
the system definition and operational concept found in Sec.  91.175 (l) 
and (m). The FAA needed to define the term ``enhanced flight 
visibility'' and the system that provides it, so it was logical to 
label that system with a name that built on enhanced flight visibility; 
hence ``enhanced flight vision system.'' To be clear that not all 
systems now called EVS would necessarily be capable of supporting 
compliance with Sec.  91.175 (l) and (m), the FAA will continue to use 
the term EFVS.

IV.31. Definitions--Topography and Enhanced Flight Vision Systems

    Comment: Another commenter recommended removing the term topography 
from the definition of EFVS.
    FAA's response: The FAA disagrees with this comment. The term 
topography was included in the definition of EFVS to be clear that the 
system would display objects on the ground and landscape.

IV.32. Synthetic Vision Systems

    Comment: Several commenters suggested changing the definition of 
synthetic vision. One commenter asked that the FAA begin to identify 
the enabling benefits of lower-cost computer-generated SVS for use in 
smaller general aviation airplanes, and to ensure that SVS operational 
capabilities occur in concert with the development of SVS equipment.
    FAA's response: As stated in the NPRM, synthetic vision system is 
defined to distinguish it from enhanced flight vision system; this 
rulemaking applies only to enhanced flight vision system. The FAA did 
not propose the situation where SVS might be authorized in the future.

IV.33. Enhanced Ground Visibility Systems

    Comment: One commenter suggested adding the term ``enhanced ground 
visibility.'' The commenter proposed defining enhanced ground 
visibility as the average forward horizontal distance, from the cockpit 
of an aircraft on the ground, at which prominent topographical objects 
or buildings may be clearly distinguished and identified by day or 
night by a pilot using an EFVS.
    FAA's response: The FAA disagrees because this is not within the 
scope of this rulemaking.

IV.34. Straight-in Approaches

    Comment: One commenter stated that the NPRM would allow EVS to be 
used on all straight-in approaches. These are allowed to be up to +/-30 
degrees to the runway centerline. TERPS allow the angular intercept to 
be displaced from the threshold for Category I approaches. The vast 
majority of HUD visual systems have only +/-15 degrees of visual (30 
degrees total) of display capability. EVS as defined in the NPRM may 
not be capable of even imaging or displaying the runway environment of 
many ``straight-in'' approaches.
    FAA's response: The rule is not limiting or predicated upon the 
field-of-view from a specific system. The rule simply states that if 
the pilot can see the required visual references at the DH or MDA using 
the EFVS, then he or she can continue the approach. If the field-of-
view on the proposed system is limiting, the pilot would not be able to 
see the required visual references and could not continue the approach 
below the DH or MDA.

IV.35. Flight Visibility or Enhanced Flight Visibility

    Comment: A commenter noted that the NPRM would require that the 
pilot must deliberately choose which, differing rule--Sec.  91.175(c) 
or Sec.  91.175(l)--he or she will use to conduct an approach. This 
imposes upon each general aviation or commercial/transport pilot the 
need to mentally maintain the differences between two highly similar 
rules on an approach-by-approach basis. Further, the rules do not 
specify if the pilot is free to switch between the requirements of the 
two differing rules during the approach to his best advantage or if he 
must choose a rule set before the approach and then stick with it 
regardless of the advantage to switching to the other rule set.
    FAA's response: This rule was written to parallel existing Sec.  
91.175(c),

[[Page 1631]]

therefore, for a pilot to gain the benefit of using an EFVS, he or she 
must know and comply with the different, but parallel requirements of 
Sec.  91.175(l). If a pilot begins an approach using a certified EFVS 
and the visual references using natural vision become more prominent, 
the pilot may continue the approach by satisfying the requirements of 
Sec.  91.175(c).
    Conversely, if a pilot begins an approach using natural vision, and 
the visual references using natural vision appear less prominent, the 
pilot may continue the approach by satisfying the requirements of Sec.  
91.175(l).

IV.36. Reduced Approach Minima

    Comment: One commenter proposed an alternative revision of Sec.  
91.175 and claimed that it updates certain outdated provisions and 
provides a basis for approval of future system or capabilities that can 
be shown to provide equivalent or better performance than currently 
acceptable systems or procedures. The commenter noted that the 
successful provisions of Sec.  91.175 were developed, used, and 
improved over many years to achieve a high level of safety when 
operating an aircraft during reduced visibility conditions. 
Additionally, the commenter stated that current rules related to 
instrument approach procedures implicitly allow (e.g., by use of 
Administrator authorizations under Sec.  91.175(a) or provisions such 
as Sec.  121.567 operations specifications) for the use of new 
technologies such as enhanced flight vision systems, required 
navigation performance, certain forms of GPS-related augmentation, or 
visual reference enhancing sensors, without having to directly address 
a specific performance standard for such authorizations.
    FAA's response: The FAA disagrees with the commenter's proposed 
rule amendment and believes it would be incorrect to predicate 
authorization for EFVS to be used in lieu of the current provisions of 
Sec.  91.175(c) based solely on the limited authority stated in Sec.  
91.175(a) for the Administrator to authorize instrument approach 
procedures other than those prescribed in part 97. The FAA believes it 
is more appropriate and more helpful to the public to publish the 
amended rule because it more clearly describes the requirements for 
operations using the EFVS to achieve an equivalent level of safety to 
the provisions of Sec.  91.175(c).

IV.37. Natural Vision

    Comment: One commenter questioned the validity of comparisons, 
stated in the NPRM, of EFVS imagery to natural vision for satisfying 
the visual requirements for continuing the approach. In particular, the 
commenter asked why the visual references as viewed in the EFVS imagery 
(using an imaging sensor operating in either infrared (IR) sensor or 
millimeter (mm) wave parts of the electromagnetic spectrum) may be any 
less natural if displayed to the pilot in the visual part of the 
spectrum.
    FAA's response: The FAA believes the comparisons of EFVS imagery 
and natural vision to be valid rationale for publishing the amended 
rule. Section 91.175(l) provides an option to use EFVS to satisfy 
visual requirements for the approach that are analogous to the time-
tested provisions of Sec.  91.175(c), and thereby makes operational 
benefits available to those who wish to equip with an EFVS.

IV.38. AC 120-29A

    Comment: Another commenter noted that AC 120-29A, section 
4.3.4.4(b), Specified Visual Reference, provides some credit to HUD 
synthetic symbology as supplemental information to external red lights. 
The commenter suggested that in the future, when the combination of a 
HUD and EFVS will be certified as an airborne equipment, it may be that 
some other supplemental aids will be identified, and that criteria to 
establish practicable minima (i.e., visibility prescribed) will have to 
be defined.
    FAA's response: AC 120-29A, paragraph 4.3.4.4, describes concepts 
upon which FAA Order 8400.13a, Procedures for the Approval of Category 
II Operations and Lower Than Standard Category I Operations on Type I 
Facilities, is founded for approving Category I ILS operations with 
lower than standard minima and Category II operations at Type I 
facilities. Unlike the provisions of the amended rule, authorizations 
based on FAA Order 8400.13a require, as a prerequisite, flight crew 
members and installed airborne systems that are approved and authorized 
for Category III operations. Unlike operations authorized per FAA Order 
8400.13a, operations conducted under provisions of the amended rule do 
not reduce the approach minima.

IV.39. Runway Environment as a Visual Reference

    Comment: One commenter asked if the pilot can descend below basic 
minimums (usually 200 feet) on a Category I glide slope beam, using 
runway-environment cues obtained solely from the EFVS.
    FAA's response: If the visual references of Sec.  91.175(l)(3), the 
approach light system (if installed) or the runway threshold and the 
touchdown zone of the intended runway, are distinctly visible and 
identifiable to the pilot at the DH or MDA using an EFVS, the pilot can 
continue the descent to an altitude of 100 feet above the touchdown 
zone elevation. The pilot must then see, using natural vision, the 
required visual references of Sec.  91.175(l)(4) that identify the 
runway environment without reliance upon the EFVS to land the aircraft.

IV.40. Barometric Altitude

    Comment: One commenter stated that no criteria are given on an 
acceptable means to determine the altitude at 100 feet above the 
touchdown zone elevation. Radar altitude may be inappropriate since 
there are no controls on terrain prior to the runway threshold for 
nonprecision approaches and not appropriate controls for Category I ILS 
approaches.
    FAA's response: The pilot may use the barometric altimeter to 
determine when the airplane has reached 100 feet above the touchdown 
zone elevation of the runway of intended landing.

IV.41. Reliance on EFVS

    Comment: A commenter requested clarification of the words ``without 
reliance on the EFVS'' as stated in Sec.  97.175(l)(4). Would this 
require turning off the EFVS?
    FAA's response: The rule does not require the EFVS to be ``turned 
off.'' The HUD/EFVS displays aircraft performance and navigation 
information, while the normal visual cues are being enhanced for 
increased situational awareness and safety. However, the pilot cannot 
rely on the EFVS to display the required visual references in Sec.  
91.175(l)(4), once the pilot descends below 100 feet above the 
touchdown zone elevation.

IV.42. Touchdown Zone Determination

    Comment: One commenter stated that EFVS as defined by the rule is 
not capable of allowing part 121 and part 135 operators to make the 
determination to touchdown within the touchdown zone of the runway of 
intended landing. HUD-style inertial flight path vector symbology can 
be utilized to determine where current descent rates are taking the 
aircraft, but they require that the EVS sensor provide indications as 
to the beginning and end of the touchdown zone.
    FAA's response: As is true today, parts 121 and 135 operators must 
manage the descent rate so that the touchdown will occur within the 
touchdown zone of the runway of intended landing. The FAA believes

[[Page 1632]]

that an EFVS can provide sufficient imagery so that the pilot can 
define the touchdown zone. If the pilot does not have sufficient 
required visual cues either with the EFVS display or looking out of the 
window to satisfy this requirement, then a missed approach must be 
executed.

IV.43. Training

IV.43.a. AFM & RFM Limitations
    Comment: One commenter asked the FAA to consider removing the 
reference in Sec.  91.175(l)(5)(iii) to compliance with the AFM and RFM 
limitations section, because it is redundant to an existing rule. 
Section 91.9 already requires that a pilot comply with the operating 
limitations specified in the AFM or RFM. Restating it here might cause 
part 121, part 125, and part 135 operators, listed in Sec.  
91.175(l)(5)(i), to think they do not have to comply with the AFM 
limitations.
    FAA's response: The FAA agrees and has changed Sec.  
91.175(l)(5)(iii) to delete references to the AFM and RFM. The 
additional requirements of parts 121, 125 and 135 are addressed in each 
of those respective parts and are mandated in the operator's operations 
specifications. The operators, once certified, are required to comply 
with the provisions of the operations specifications and all approved 
or accepted training and/or checking programs. The operator is 
responsible for the training and checking of each pilot using the EFVS 
if authorized under the pertinent and applicable parts of the Code of 
Federal Regulations. Operations conducted under part 91 do not require 
training or checking on the EFVS, although pilots who operate EFVS 
equipped aircraft are potentially subject to being checked on such EFVS 
equipment during currency and proficiency checks of part 61.
IV.43.b. No Additional Training
    Comment: A commenter noted that no additional training for the use 
of EFVS should be required under part 61 for general aviation pilots 
operating under part 91.
    FAA's response: FAA agrees that a specific training requirement for 
the use of EFVS for part 91 operators does not need to be added to the 
rule. However, a Flight Standardization Board (FSB) did evaluate one 
system and determined that additional crew training was required, 
documented the required training in the FSB report and all pilots 
operating aircraft subject to that FSB report with the FAA evaluated 
EFVS system will have an operating limitation in the AFM requiring 
pilot training.
IV.43.c. Additional Training and Proficiency
    Comment: One commenter stated that the rule does not address part 
61 as far as pilot training requirements, but does address parts 121, 
125, and 135 and states that operations under 91 would be authorized. 
The rule requires pilots to be proficient and qualified in accordance 
with part 61. Part 61 covers basic instrument qualifications under 
Sec.  61.57 and an additional requirement for Category II operations 
under Sec.  61.67. The commenter suggested that additional training and 
proficiency requirements for operations (involving) EFVS should be 
established to ensure the same level of safety as for Category II 
operations, since this new technology is going to allow pilots to 
operate at lower than normal minimums.
    FAA's response: The FAA believes that pilot training requirements 
for applicants under the Airline Transport Pilot and Aircraft Type 
Rating, Practical Test Standards for Airplane and Airline Transport 
Pilot and Aircraft Type Rating, Practical Test Standards for Helicopter 
should remain pilot certificate specific. Pilots obtaining certificates 
under the provisions of part 61 are subject to testing and proficiency 
checks under Sec.  61.58, may need to obtain training in order to pass 
the check on all of the installed equipment on an aircraft, and must, 
at the least, demonstrate proficiency in the use of the installed 
equipment to the same standards required for the original issuance of 
the certificate. Also, all pilots who conduct operations under part 91 
must meet the currency requirement of Sec.  61.56, which may include 
the aircraft and equipment. The FAA is not proposing to modify the 
existing pilot requirements of part 61.
    The FAA disagrees with the commenter's reasoning that additional 
training and proficiency requirements are necessary for EFVS operations 
because the new technology will enable pilots to operate at lower than 
normal minimums. The use of EFVS does not reduce approach minimums; 
EFVS is an alternate to the requirements of Sec.  91.175(c).
    Part 61 does not require training prior to authorizing Category II/
III operations or other procedures beyond the initial pilot 
certification process. Nor does the FAA believe that it is appropriate 
to mandate training requirements beyond that of the initial 
certification process or flight review process for operators under part 
91 conducting standard instrument approach procedures.
IV.43.d. Crew Training
    Comment: One commenter stated that due to the specifics of 
interpreting an IR image, crew training will be an important issue and 
needs to be carefully addressed. The commenter comments that specific 
simulation models need to be defined as they exist for Category III HUD 
landing system qualifications, and that typical and worst case 
situations must be defined for simulator use (windshear, crosswind, 
visibility, obstructions, etc.) in order to ensure that the crew can 
reach an acceptable proficiency level with the system. Crew 
qualification should be based on performance obtained in the simulator.
    FAA's response: The FAA disagrees with limiting crew training to 
the simulator. Holders of air carrier certificates and commercial 
operator's certificates are held to higher standards and are therefore 
required to provide FAA-approved training programs developed for the 
type of operation to be conducted. Such programs, whether training or 
checking and testing, may take advantage of any appropriate FSB Report 
issued.
    While the FSB Report is not regulatory in nature it provides the 
FAA principal inspector with guidance as to the proper content, 
duration, and intent of any training program submitted for approval or 
acceptance in accordance with the operating rule. In addition, 
facilities that provide training on behalf of manufacturers rely on 
recommended training such as an FSB Report when developing training and 
checking programs for their customers.

IV.44. Requirements for the Airplane Flight Manual (AFM)

    Comment: One commenter stated that the operational limitations for 
an EFVS should be included in the AFM and not included in a rule.
    FAA's response: The FAA agrees with the commenter that some 
operating limitations, in addition to those specified in this final 
rule, may be placed in an AFM or RFM, depending on the certification 
evaluation of a particular applicant's EFVS. The FAA disagrees that all 
operating limitations should be specified in the AFM or RFM.

IV.45. Air Carrier Operations Specifications Requirements

    Comment: One commenter stated that the NPRM includes a proposed 
requirement to obtain operations specifications authorization for air 
carriers (proposed Sec.  91.175(l)(6)). Operations specifications 
approval is always required for decreased

[[Page 1633]]

minimums, but EFVS does not change the minimums. The EFVS allows the 
pilot to visually acquire the cues specified in Sec.  91.175 to descend 
below DH, but does not affect the minimums given on the approach 
procedure. Therefore, operations specifications approval should not be 
required. The requirement for operations specifications approval adds 
an unwarranted financial burden on the operator, and may take a very 
long time to achieve because most principal operations inspectors do 
not have the background knowledge to make this evaluation. The FAA 
certification pilots and engineers are required to accomplish extensive 
testing to validate the EFVS. The commenter considers that there is no 
reason to require an additional approval, beyond that achieved by STC.
    FAA's response: The FAA agrees that use of EFVS does not change the 
instrument approach minima. However, the FAA believes that Sec.  
91.175(l)(6) should not be revised to incorporate the commenter's 
recommendation. Part 119 and part 125 certificate holders and part 129 
operations specifications holders that use a HUD today for the conduct 
of instrument approach procedures require authorization in their 
operations specifications. This authorization includes training on the 
equipment and procedures to fly instrument approach procedures. 
Likewise, the EFVS, which also includes a HUD, will require training in 
the use of a HUD symbology and procedures developed by the operator for 
the specific equipment being used. The FAA also does not agree that 
this is an unwarranted financial burden on the operator or that 
principal inspectors will not have the background or knowledge to 
evaluate the air carrier's program. Principal inspectors routinely 
authorize operations that require a HUD and in fact work directly with 
the operator to develop these programs and procedures. To assist the 
principal inspectors, the FAA will provide handbook guidance.

IV.46. Foreign Aircraft Certification

    Comment: One commenter states that the proposed rule violated 
existing bilateral agreements, and precludes the possibility of the FAA 
ever accepting an EFVS approval by another authority through the 
bilateral process without additional rulemaking. Another commenter 
stated that this proposed rulemaking seems to introduce discrimination 
towards non-U.S. manufacturers.
    FAA's response: The intent of the rule, referenced in Sec.  
91.175(l)(7), was to be fully consistent with the provisions of 
existing bilateral agreements for aircraft certification. Under such an 
agreement, a non-U.S. aviation authority may, on behalf of the FAA, 
find compliance to FAA certification requirements. The FAA would 
validate such findings and issue a U.S. type certificate (i.e., type 
certificate, amended type certificate, or supplemental type 
certificate, as applicable). U.S. type certificates would be available 
for installation of non-U.S. manufactured EFVS, just as they are for 
installation of other types of equipment today, whether manufactured in 
the U.S. or not.
    The FAA revises the language in Sec.  91.175(l)(7) to clarify that 
the FAA does not discriminate against foreign operators or non-U.S. 
manufacturers.

IV.47. Equipment Requirements for Subpart C

    Comment: One commenter stated that the proposed rulemaking did not 
clearly define equipment requirements, and that there was no proposed 
rulemaking regarding EFVS in subpart C of part 91. The commenter asked 
the FAA to clarify EFVS equipment requirements and establish an EFVS 
TSO that clarifies the design requirements for enhanced flight vision 
sensors or equipment, excluding the HUD.
    FAA's response: The FAA disagrees that a requirement for EFVS 
equipment should be added to part 91 subpart C. The rule allows for the 
use of an EFVS to determine ``enhanced flight visibility'' in lieu of 
``flight visibility.'' An EFVS is not required equipment, except for 
those operators choosing to use this alternative method of operation 
below DH or MDA.
    Advisory Circular guidance for certification of EFVS, and perhaps 
even a TSO, might be issued in the future. In the meantime issue papers 
and special conditions may be used to certify EFVS based on its ability 
to perform its intended function and the required characteristics as 
specified in the rule, a system safety assessment, and existing 
certification criteria for software, programmed logic devices, head-up 
displays, and other criteria, as applicable to the EFVS design. In 
addition to criteria contained in issue papers from previous 
certifications, industry documents, such as Society of Automotive 
Engineers (SAE) Aerospace Standard (AS) 8055 and Aerospace Recommended 
Practices (ARP) 5288 provide a useful starting point.

IV.48. Clarification on Maneuvering

    Comment: A commenter requested that the FAA clarify the meaning of 
the phrase ``which is suitable for maneuvering the aircraft'' as stated 
in Sec.  91.175(l)(7).
    FAA's response: The FAA means that the EFVS display, because it is 
being used as the pilot's primary flight reference during the approach, 
at least down to 100 feet above the touchdown zone elevation, needs to 
provide effective visual feedback to the pilot for manual control of 
the airplane. In particular, the alignment and motion of the EFVS 
imagery, attitude and guidance symbology must faithfully represent 
airplane motions, without significant jitter, jerkiness, or latency 
(i.e., display lag, slow update rate) that would adversely affect the 
pilot's ability to manually control the airplane with satisfactory 
precision, stability and workload. In addition to EFVS display 
dynamics, many other factors such as field of view, control of display 
luminance, clutter, and display blooming could significantly degrade 
pilot performance and workload while manually controlling the airplane 
in the approach.

IV.49. Certification of an EFVS

    Comment: Several commenters noted that the EFVS features and 
characteristics specified in the proposed Sec.  91.175(m) were 
certification requirements, not operational requirements, and should be 
deleted from the rule and moved to parts 23 and 25 and/or associated 
advisory material. Another commenter said that the specified 
characteristics are not quantified and lack detail without reference to 
a Minimum Operational Performance Specification (MOPS) or some other 
technical standard. Certification requirements, processes, and 
regulations need to be developed and issued expeditiously.
    FAA's Response: The FAA believes that in order to safely and 
effectively perform approach operations under the provisions of Sec.  
91.175(l), there are certain essential characteristics and features 
that must comprise the EFVS. Therefore, the FAA believes this list 
specified in paragraph (m) constitute operational requirements. The 
items in this list were deliberately stated in general terms, well 
enough to capture the essential requirements but without over-
specifying the system design to permit as much design flexibility as 
possible.
    The operationally essential features of the EFVS are that the image 
and spatially referenced flight symbology is displayed so that they are 
aligned with and scaled to the external view (conformally) on a HUD 
with essential flight instrument information. The image must be 
conformal because it

[[Page 1634]]

provides an alternative, enhanced forward view that could be used in 
lieu of flight visibility to meet the prescribed visibility 
requirements.
    The imagery must be displayed on a HUD because the FAA believes 
that the safety of an approach operation conducted under Sec.  
91.175(l) depends on the pilot looking forward along the flight path 
(i.e., looking at and through the imagery to the out-of-the window 
view) to readily enable a transition from reliance on the EFVS imagery 
above 100 feet height above the touchdown zone elevation to reliance on 
the out-the-window view without reliance on EFVS. The FAA believes that 
if the pilot must scan up and down between a head down display of the 
image and the out-the-window view, then the transition would be 
hindered by the delay of repeatedly re-focusing from one view to the 
other.
    The imagery must be displayed with essential flight instrument 
information because the FAA believes that once the EFVS is being relied 
on for descent and operation below DH, or MDA, it should become the de 
facto primary flight reference. The pilot requires continuous awareness 
of the flight information while using the EFVS imagery. This awareness 
would be unsatisfactorily degraded by repeated scanning from head up, 
to head down, and back.

IV.50. Performance-Based Advisory Materials

    Comment: Several commenters said that an advisory circular or 
advisory material is needed to support the rule, but that the 
development of new advisory material need not delay adoption of a 
suitable enhanced vision system rule. Another commenter recommended the 
FAA begin work on an AC to establish airborne equipment certification 
standards, training, and AFM endorsements that ensure that the items 
referenced in Sec.  91.175 are distinctly visible with the EVS.
    Another commenter requested that the FAA draft specific EVS 
technical and system design language, along with suggested 
certification methodologies and place in appropriate advisory material.
    Still another commenter saw advisory material as the means for 
certification through performance standards. This commenter noted that 
the proposed Sec.  91.175(m)(1) of the rule, which addresses features 
and characteristics, states: ``An electronic means to provide a display 
of the forward external scene topography (natural or manmade features 
of a place or region especially in a way to show their relative 
positions and elevation) through the use of imaging sensors, such as a 
forward looking infrared, millimeter wave radiometry, millimeter wave 
radar, and low-light level image intensifying.'' Similar wording also 
appears in the EFVS definition in part 1. Neither the rule nor the 
definition should cite specific current-generation technology, but 
rather should reflect a performance or implementation requirement that 
can be further developed in advisory material. For example, the sensor-
based imaging elements of the EFVS shall be appropriately located on 
the aircraft, shall employ a sensor technology appropriate to the 
intended function, and the combination of the sensor and HUD shall 
provide resolution and other system attributes coincident with the 
generation of a high-quality conformal image. Certification criteria 
for future EFVS should be the subject of an AC. As an example, the use 
of a HUD system is required in the proposed rule. The commenter 
believed this language may not stand the test of time and therefore 
requests that the language be changed to reflect the use of a display 
and symbology set certified for the intended function.
    FAA's response: The FAA believes that Sec.  91.175(l) and (m) 
provide operational requirements that are not specific to a particular 
technology design. The FAA agrees that advisory material for 
certification of EFVS will be useful, but not that such material should 
replace Sec.  91.175(m), which specifies essential operational 
requirements for EFVS. At this time, until more experience is gained 
with the potential variations of EFVS designs, it is premature to 
establish such guidance. Until such guidance is available, issue papers 
and special conditions may be used to certify EFVS based on its ability 
to perform its intended function and required characteristics as 
specified in the rule, a system safety assessment, and existing 
certification criteria for software, programmed logic devices, head-up 
displays, and other criteria, as applicable to the EFVS design. In 
addition to criteria contained in issue papers from previous 
certifications, industry documents, such as Society of Automotive 
Engineers (SAE) Aerospace Standard (AS) 8055 and Aerospace Recommended 
Practices (ARP) 5288 provide a useful starting point. The FAA expects 
that a working committee of the Society of Automotive Engineers (SAE) 
or similar group will undertake further efforts to develop industry 
certification standards for EFVS that could support EFVS advisory 
material.
    The FAA believes it is necessary to include Sec.  91.175(m) in the 
rule because the alternative means outlined in Sec.  91.175(l) for 
descent and operation below DH or MDA requires an EFVS with such 
features and characteristics. Other technology solutions for conducting 
low visibility approach and landing operations, such as SVS, would 
require a different operational.

IV.51. Display Comments

IV.51.a. Head-Up or Head-Down Displays
    Comment: There were several comments stating that the FAA should 
allow both a head-up display or a head-down display for EFVS in 
paragraph (m) and should permit alternate display locations. One 
commenter suggested revising paragraph (m)(2) to say, ``The EFVS sensor 
imagery and aircraft flight symbology (i.e., at least airspeed, 
vertical speed, aircraft attitude, heading, altitude) are presented on 
head-up display or other certified display within the pilot's primary 
field of view and clearly visible to the pilot flying in his or her 
normal position and line of vision and looking forward along the flight 
path.'' This commenter also stated that when transitioning from 
``enhanced flight visibility'' to ``flight visibility'' the pilot would 
only make a slight change in focus, very similar to the transition 
taking place when conducting currently regulated approaches down to low 
minimums.
    FAA's response: The FAA disagrees with the recommendation to permit 
any certified head-down display for EFVS.
    The rule requires that EFVS include a head-up display rather than 
the alternative of a head-down display because the pilot is conducting 
an instrument approach procedure in lower visibility conditions, but 
with no change in the prescribed instrument approach minima and must 
accomplish several visually-related judgments and control tasks in 
quick succession. While the regulatory requirements for the use of EFVS 
are analogous to the conventional requirements for descent and 
operation below DH or MDA, the pilot needs to use the imagery, the 
flight reference information, and eventually the outside view, at the 
same time. The pilot must be able to look for the outside visual 
references in the same location as they appear in the EFVS image and 
readily see them as soon as visibility conditions permit, without any 
delays or distraction due to multiple head-up/head-down transitions.
    When scanning between the head-up and head-down views, it takes 
additional time for the pilot to reacquire the information in each view 
and for the pilot's eyes to readjust for differences in light level and 
changes in focus between

[[Page 1635]]

optical infinity and the distance to the instrument panel (on the order 
of 24 inches). Repeated scanning between the head-up and head-down 
views would be distracting, increase pilot workload and potentially 
degrade path performance during a critical phase of flight.
    These effects are avoided by displaying the EFVS imagery and flight 
information on the HUD. Between the DH or MDA and 100 feet, the pilot 
will be able to look for the outside visual references in the same 
location as they appear in the EFVS image and readily see them as soon 
as visibility conditions permit, without any delays or distraction due 
to multiple head-up/head-down transitions and without interruption of 
the view of essential flight information.
IV.51.b. Head-Up Display
    Comment: One commenter stated that HUD presentation and modern 
display symbols including flight path vector, reference flight path 
angle, and horizon marks (and ideally airspeed error and trend) have 
been repeatedly shown to dramatically decrease workload and increase 
landing accuracy when overlaying the actual runway environment.
    FAA's response: The FAA agrees with the commenter that additional 
head-up display symbology should be required for the EFVS. Section 
91.175(m)(2) is therefore amended to require a FPV and a flight path 
angle reference cue. Because this rulemaking has created an exception 
to the time-tested existing safety standards in Sec.  91.175(c), it is 
within the scope of the notice to tighten the conditions for such an 
exception at the final rule stage when, as here, potential safety 
problems and solutions are identified by commenters. In other words, 
the exception language as originally proposed would not have required 
FPV as a condition for the EFVS to be used, adding FPV as a required 
feature narrows the proposed exception and thus is within the scope of 
the proposed exceptions.
IV.51.c. Guidance, Flight Path Vector (FPV), and Other Symbology
    Comment: Several commenters stated that the rule should 
specifically require additional items of flight information, including 
the flight path, guidance, conformal flight path vector (FPV) and cues 
for energy state control.
    One commenter stated that the rule is not clear about the need for 
guidance in the EFVS display and recommends that the rule be amended to 
include a requirement for flight director or some form of command 
guidance, conformal presentation of FPV, and cues for energy state 
control.
    In a related comment, another person stated that the FAA should 
continue to require the use of HUD, that ILS guidance should also be 
displayed on the HUD, and that the EFVS should have a head-up guidance 
system, not just a HUD.
    Similarly, other commenters stated that the FAA omitted the FPV, an 
important symbology cue, in its list of required features and 
characteristics of EFVS in paragraph (m). This symbology cue combines 
drift angle and flight path angle to show where the aircraft is 
actually going (also known as velocity vector) as opposed to where the 
nose is pointed (longitudinal axis).
    FAA's response: The FAA agrees with the comments that the rule 
should be revised to require EFVS to display flight path (i.e., the 
intended approach path as shown by lateral and vertical path deviation 
indications), command guidance, a conformal FPV, and a flight path 
angle reference cue. The FAA does not agree that the rule should be 
revised to mandate other suggested symbology cues, such as cues for 
energy state control, airspeed error and trend.
    The FAA has revised the rule to require that the EFVS display 
lateral and vertical approach path deviation indications (e.g., 
localizer, glideslope or course deviation indications (CDI)) and 
command guidance (e.g., repeat display of head down flight director, or 
HUD unique command guidance cue) as appropriate for the kind of 
approach to be flown. The rule requires approach path deviations 
because they are essential to conduct the approach and the pilot must 
not be required to scan head down for the information. The rule 
requires command guidance because, when available and appropriate for 
the approach being flown, it reduces pilot workload, increases path 
tracking performance, and was found essential for ILS approaches during 
proof of concept evaluation of a previously certified enhanced vision 
system. For types of approaches without a vertical navigation aid, 
(e.g., localizer-only, or VHF omni-range station (VOR)), neither 
vertical path deviation indications nor vertical guidance is required. 
The FAA believes that the addition of a FPV and a flight path angle 
reference cue provides effective tools to monitor and maintain a safe 
vertical path from the DH/MDA to the desired touchdown point on the 
runway. These changes are within the scope of the notice because in 
proposed Sec.  91.175(m)(2) the FAA listed broad examples of the types 
of flight symbology that would be required for safety purposes. The 
items listed in Sec.  91.175(m)(2) were intended to be the minimum 
flight symbology features on the HUD. The FAA is adding similar flight 
symbology requirements to the final rule. By adding these additional 
required features, the FAA is narrowing the circumstances under which 
an EFVS could be used as an exception to the existing standards in 
Sec.  91.175(c).
    The rule does not explicitly specify other flight symbology cues, 
such as those recommended by the commenters, because the FAA does not 
have sufficient data to mandate them unconditionally. Such cues have 
been essential features of previously approved HUD landing guidance 
systems, but the intended function of these systems (e.g., Category III 
landings) is different from EFVS, which is used to satisfy Sec.  
91.175(l). Nevertheless, the FAA recognizes that such cues have been 
found to enhance pilot performance, reduce workload, and believes they 
might mitigate characteristics of EFVS imagery, compared to natural 
vision in visual meteorological conditions (VMC), that are significant 
for maneuvering the airplane. The FAA believes that the entire EFVS, 
which includes the image, flight information and graphic symbology, not 
just the imagery alone, must be suitable for maneuvering the airplane. 
The FAA will evaluate each EFVS, including the symbology cues, for its 
ability to satisfy the operational and safety objectives of the rule, 
including its suitability for maneuvering the airplane. Based on 
products already certified, the FAA anticipates that most, if not all 
EFVS designs would include such features anyway.
IV.51.d. EFVS for Situational Awareness
    Comment: One commenter stated that the FAA should not preclude the 
use of EFVS for situational awareness.
    FAA's response: This rule addresses only EFVS used to permit 
descent and operation below the DH or MDA, when flight visibility 
minima are not met.
IV.51.e. Design Eye Position
    Comment: One commenter stated that a pilot's normal seating 
position may not coincide with the design eye point, the position at 
which the cockpit equipment was designed and certified. The commenter 
stated that the position from which the pilot views the EFVS HUD is 
critical to clearly seeing the EFVS imagery and flight symbology and 
recommended that Sec.  91.175(m)(2) be revised to read: ``The EFVS 
sensor imagery and aircraft flight symbology (i.e., at least airspeed, 
vertical speed, aircraft attitude, heading, altitude) are presented on 
a head-up display so that

[[Page 1636]]

they are clearly visible to the pilot viewing from the design eye 
position and looking forward along the flight path.''
    FAA's response: The FAA agrees with the commenter that the position 
from which the pilot views the EFVS HUD is significant. The most 
significant effect of a displacement from design eye position is that 
some displayed information may not be visible to the pilot. For 
certification of head-up displays, the FAA uses criteria described in 
AC 25.773-1 (Pilot compartment view design considerations) and an FAA 
issue paper titled ``Head-up display (HUD) installation, system design 
policy and guidance,'' which will also be applied to EFVS, that 
concerns variations of the pilot's viewpoint that constitute what has 
been called the ``head motion box.'' This head motion box has minimum 
dimensions in three axes and when the pilot's eyes view the HUD while 
located in this volume, all essential information must be visible in 
the HUD. The FAA agrees with the intent of the commenter's 
recommendation, but believes that the recommended revision is not 
necessary, because current HUD certification criteria will be applied 
to EFVS and if the essential information is not clearly visible from 
the design eye point, the EFVS could not perform its intended function.
IV.51.f. Display Conformality and Parallax Errors
    Comment: One commenter noted that there is no requirement in Sec.  
91.175 (m) regarding where the EFVS sensor is installed on the 
airplane. The commenter stated that it is of the utmost importance that 
EFVS imagery is displayed conformally with the outside view and that 
parallax error must be very small, as it is with currently-certified 
HUD guidance systems. The commenter recommended that the FAA revise the 
rule to add a requirement that the EFVS sensor be installed in a 
location such that the image is conformal to the outside view with no 
more than 4 milliradians (mrad) of parallax error.
    FAA's response: The FAA agrees with the commenter that the EFVS HUD 
display must be conformal and that excessive parallax error, due to the 
displacement of the sensor location from the pilot's line of sight, 
would not be acceptable. Parallax is one error source that degrades 
conformality. In fact, all HUD's currently certified for approach and 
landing operations, with and without imagery, have this design feature. 
Therefore, the FAA revised Sec.  91.175 (m)(2) to require that the EFVS 
imagery, attitude symbology, FPV and other cues referenced in the 
imagery and outside view must be presented aligned with, and scaled to, 
the external view. This change is within the scope of the rulemaking 
because an identified shortcoming in the draft exception (i.e., Sec.  
91.175(l)), to the longstanding Sec.  91.175(c) standard, is being 
corrected by narrowing the kinds of devices that would meet the 
exception criteria.
    As the commenter stated, conformality of the image and any 
associated symbology means, that the angular orientation and scale 
match the external view. Objects visible both in the image and out the 
window would line up exactly when viewed by the pilot in the normal 
seated position (i.e., at the design eye point). As the runway 
threshold, approach light system, and so forth come into view out the 
window, they would show up in the same location as they already appear 
in the EFVS image.
    This operational rule will not quantitatively specify the maximum 
parallax (i.e., alignment) error, because the error can vary with 
distance (i.e., more angular error at short distances) and an 
acceptable limit may depend on the intended function. The amount of 
parallax error that is acceptable for an approach with a transition to 
outside visual cues no lower than 100 feet above the touchdown zone 
elevation might differ from what is needed for a landing system. 
Industry standards, for example Society of Automotive Engineers (SAE) 
Aerospace Standard AS8055 ``Minimum Performance Standards for Head-Up 
Display (HUD),'' contain different values than those recommended by the 
commenter.
    During EFVS certification, the FAA will evaluate the display to 
determine that the display is sufficiently conformal to the outside 
view for its intended function, and that parallax error, if any, is not 
excessive or misleading to the pilot.
    Some information displayed in the HUD is not ``spatially 
referenced'' and therefore does not need to be conformal. For example, 
airspeed, vertical speed, altitude and some other data can be shown in 
a variety of non-conformal formats, such as linear tapes and round 
dials. Both conformal and non-conformal heading formats have been found 
acceptable.
IV.51.g. Power System for an EFVS
    Comment: One commenter stated that in case of a single failure 
between 200 feet and l00 feet (engine or generator), a total loss of 
enhanced vision would occur while the pilot most needs the EFVS to 
maintain clearance with obstacles and to maintain runway alignment. The 
commenter proposed that the rule should specify that the EFVS design 
would guarantee the segregation between EFVS failures and failures 
affecting aircraft path control and performance (ILS and HUD should not 
be powered by the same electrical source as the EFVS for instance).
    FAA's response: The FAA disagrees that this requirement should be 
added to the operational rule. In cases where the EFVS fails between 
the decision height and 100 feet above the touchdown zone elevation, 
the rule, Sec.  91.175(e), requires that a missed approach be executed 
if the requirements of (c) or (l) are not met. However, airworthiness 
certification requirements for EFVS system architecture, redundancy and 
independence of power supplies may result from compliance with the 
system safety requirements (e.g., Sec.  23.1309, Sec.  25.1309, etc.).
IV.51.h. Independent Displays
    Comment: One commenter requested clarification as to whether the 
HUD must be independent of the head-down primary instruments.
    FAA's response: Flight information (e.g., airspeed, altitude, 
direction, attitude, path deviation) displayed on a pilot's EFVS HUD 
does not need to be independent from the flight information displayed 
on the pilot's head down primary flight references. Based on past 
experience with HUD's approved as flight display for Category II and 
Category III approach operations, this independence is not necessary. 
However, as the certification rules require, the pilot's and co-pilot's 
displays of flight information must be independent.

IV.52. Comments on Economic Evaluation

    Comment: A commenter stated that the NPRM could create significant 
unnecessary cost obstacles for both operators and manufacturers in the 
United States by inappropriately and unfairly favoring technology that 
is not mature, may not work, and may not be safe, compared with other 
proven technologies. This situation has significant indirect 
competitive costs, design costs, liability costs, and aircraft 
operating penalty costs, which are not addressed by the NPRM.
    FAA's response: The FAA disagrees. Because the rule is optional, 
the FAA believes that the available technology should be allowed, 
especially when it can enhance safety during low visibility conditions. 
The FAA disagrees with the statement that this technology is unsafe

[[Page 1637]]

when used in accordance with the operating rules adopted today.

V. Contact With Aircraft Manufacturer for Confirmation of Performance 
Capabilities

    During the comment period, several FAA employees worked with one 
aircraft manufacturer to evaluate the operational and technical 
performance in the use of an EVS-equipped aircraft and simulator 
system. This was necessary to confirm performance and limitations of 
this technology in an operational environment.

VI. Differences Between the NPRM and Final Rule

    As discussed under ``III. Related Rulemaking Actions,'' the FAA 
included some terminology in the EFVS NPRM that had been proposed 
earlier in the RNAV NPRM. Because, as of the issuance of this final 
rule, the RNAV rulemaking action has not been completed, those proposed 
changes are not being adopted. Specifically those proposed changes are 
as follows.
    In Sec. Sec.  91.175(c), 121.651(c) and (d), 125.381(c)(2), and 
135.225(c)(3)(ii) the terms ``DA'' and ``DA/DH'' are not adopted in 
this final rule. Therefore, all proposed references to ``DA'' and ``DA/
DH'' read ``DH.''
    In Sec. Sec.  125.381(c)(1)(i) and 135.225(c)(1)(i) the words 
``precision approaches'' are replaced with the abbreviation ``ILS.''
    In Sec.  121.651(d), the word ``person'' is replaced by the word 
``pilot.'' Also, the proposed change replacing the words ``an 
instrument approach procedure other than a Category II or Category 
III'' with ``a Category I precision approach'' is not adopted. In 
addition, the proposed change replacing the words ``a operative ILS and 
an operative PAR, and both'' with ``an operative PAR and another 
operative precision instrument approach system, and both the PAR and 
the precision approach'' is not adopted.
    In Sec. Sec.  125.381(c)(1)(i) and 135.225(c)(1)(i) the term 
``APV'' is not adopted in this final rule. Therefore, all proposed uses 
of the term APV are deleted.
    In addition, as a result of comments received, the FAA revises the 
final rule as follows:
    Category I operations--Section 91.175(l) is amended to include in 
the rule text that this exception only applies to a ``* * * straight-in 
instrument approach procedures other than Category II or Category III * 
* *.''
    Visual references--Under Sec.  91.175 (l)(3) of this final rule, 
the visual references that the pilot can use at the DH or MDA to 
continue the approach are clarified such that ``runway threshold and 
the touchdown zone,'' as proposed in the NPRM, includes the approach 
light system, if installed, or both the runway threshold and the 
touchdown zone. This is discussed in detail under ``IV.3. Visual cues 
(visual references)'' above. Combined, these references form a pattern 
of recognition whereby the pilot may safely continue the descent to 100 
feet above the touchdown zone elevation.
    Qualification requirement--Section 91.175(l)(5) is revised to 
change the qualification requirement to one of currency and to delete 
reference to the limitations specified in the Airplane or Rotorcraft 
Flight Manual.
    Additional operational requirements--Section 91.175(m)(2) is 
revised to include the additional operational requirements of command 
guidance, path deviation indications, and flight path vector, flight 
path angle reference cue to be displayed on the HUD. This change 
narrows the scope of acceptable EFVSs by stating only those systems 
that have these additional features will be permitted to operate under 
Sec.  91.175(l).
    EFVS display--Section 91.175 (m)(2)(i) is added to include the 
additional operational requirement that the EFVS imagery and external 
scene topography must be presented so that they are aligned with and 
scaled to the external view. The FAA is also adding (m)(2)(ii) to 
specify the essential features and intended function of the ``flight 
path angle reference cue.'' In order to perform its intended function, 
the cue needs to be set by the pilot to the desired value for the 
approach, the pilot needs to see the cue in the context of pitch scale 
to verify that it is correctly set, and it needs to be shaped and 
located so as to allow the pilot to monitor the airplane's vertical 
path. This is a descending path along the selected glide path angle and 
is anchored to the desired touchdown point. To accommodate these 
changes, paragraph (m)(3) is redesignated as (m)(2)(iii); paragraph 
(m)(4) is redesignated as (m)(3); and (m)(5) is redesignated as (m)(4).
    Topographical features--The FAA is amending Sec.  91.175 (m)(1) to 
state that an EFVS must be able to display topographical features of 
the airport environment. It is not the FAA's intent to require an EFVS 
to detect all obstacles to ensure obstacle clearance in the visual 
portion of the final approach segment.

VII. Discussion of the Final Rule

    Possible operational benefits--This final rule will not require the 
use of an EFVS. However, using an EFVS would allow operations in 
reduced visibility conditions that would not otherwise be possible.
    Category I operations--This final rule will retain the existing 
straight-in-landing instrument approach minima for other than a 
Category II or III approach, and will authorize the pilot to use FAA-
certified EFVS imaging-sensor technologies to determine enhanced flight 
visibility. This final rule will allow a pilot to fly straight-in-
landing instrument approach procedures other than Category II and III 
procedures and descend below the DH or MDA using an EFVS.
    Category II and Category III ILS approach procedures--The final 
rule does not prohibit the use of an EFVS for Category II and III ILS 
approach procedures. The use of EFVS during Category II or Category III 
operations must be specifically authorized by the Administrator. Any 
future proposed enhanced flight vision systems for these approaches 
would have to comply with the more stringent reliability, redundancy, 
other criteria as discussed in the FAA's response to comments and as 
prescribed in applicable sections of 14 CFR and applicable advisory 
circulars. But the use of EFVS in Category II or III ILS approaches 
does not lower minimums that would otherwise apply for aircraft not 
equipped with EFVS conducting Category II or III ILS approaches.
    Visual references--Section 91.175 (c)(3) lists ten visual 
references, of which only one is required for the pilot to descend 
below the DH or MDA. The visual references are: (1) The approach light 
system, (2) threshold, (3) threshold markings, (4) threshold lights, 
(5) runway end identifier lights, (6) visual glideslope indicator, (7) 
touchdown zone or touch down zone markings, (8) touchdown zone lights, 
(9) runway or runway markings, and (10) the runway lights identifying 
the approach end of the runway. If the approach light system is used as 
the reference, the pilot may not descend below 100 feet above the 
touchdown zone elevation unless the red terminating bars or the red 
side row bars are also distinctly visible and identifiable. As a 
parallel, under paragraph (l)(3), the final rule states that, when 
using an EFVS, the approach light system (if installed), or the runway 
threshold (lights or markings), and the runway touchdown zone (lights 
or markings) would have to be distinctly visible and identifiable to 
the pilot before descending below the DH or MDA for the pilot to 
continue the approach. See the discussion under

[[Page 1638]]

``IV.3. Visual cues (visual references)'' above.
    Because the imaging-sensor technologies may not sense or display 
all of the identifying features of the visual references (e.g., may not 
distinguish colors of lights), the FAA in this final rule is clarifying 
the visual references listed in Sec.  91.175(l)(3), as discussed under 
``IV.3. Visual cues (visual references)'' above. Taken together, these 
visual references form a pattern of recognition for the pilot to safely 
continue the approach to 100 feet. At 100 feet above the touchdown zone 
elevation and below, there would have to be sufficient flight 
visibility (without reliance on an EFVS) for the lights or markings of 
the threshold; or the lights or markings of the touchdown zone of the 
intended runway to be distinctly visible and identifiable to the pilot 
to continue to a landing.
    Pilot qualifications--To use the EFVS equipment while conducting an 
instrument approach procedure under this final rule, the pilot(s) must 
be current and proficient in accordance with existing applicable 
requirements in part 61, 121, 125 or 135. Each foreign pilot would have 
to be qualified in accordance with the requirements of the operator's 
State civil aviation authority. Foreign air carriers will be required 
to comply with this rule and their operations specifications. For all 
operators, this will include knowledge of the EFVS requirements, 
operational procedures, and limitations as prescribed in the approved 
Airplane or Rotorcraft Flight Manual for the specific system.
    Certification process--An EFVS used under this final rule would 
have to provide the pilot with sufficient guidance and visual cues so 
that the pilot could manually maneuver the aircraft to a landing on the 
intended runway. The sensor image alone may not be suitable to maneuver 
the aircraft. For the pilot(s) to maximize situational awareness while 
maneuvering the aircraft in the visual segment of the instrument 
approach procedure, at low altitudes and reduced visibility conditions, 
the FAA requires that several key components be provided by an EFVS to 
provide an adequate level of safety. The EFVS sensor imagery must be 
presented on a HUD that is centrally located in the pilot's primary 
field of view and in the pilot's line of vision along the flight path. 
The imagery must be real-time, independent of the navigation solution 
derived from the aircraft avionics, and must be clearly displayed so 
that it does not adversely obscure the pilot field of view through the 
cockpit window.
    Aircraft flight symbology, such as airspeed, vertical speed, 
attitude, heading, altitude, command guidance (e.g., repeat display of 
head down flight director, or HUD unique command guidance cue) as 
appropriate for the kind of approach to be flown, and lateral and 
vertical approach path deviation indications (e.g., localizer, 
glideslope or course deviation indications (CDI)) must be provided. A 
flight path angle reference cue and FPV also must be displayed on the 
HUD and be clearly visible so that the pilot can monitor and maintain a 
safe vertical path from the DH/MDA to the desired touchdown point on 
the runway.
    The displayed sensor imagery and aircraft symbology may not 
adversely obstruct the pilot's vision looking through the aircraft's 
forward windshield. The EFVS imagery, attitude symbology, FPV and other 
cues which are referenced to the imagery and outside view must be 
presented so that they are aligned with and scaled to the external 
view.
    The FAA will conduct the certification and evaluation process in 
accordance with published guidance and current policy. The FAA will 
also evaluate the capabilities, operational procedures, training and 
limitations for the specific system as it is designed and flight-
tested. In all cases, the applicant for an airworthiness type design 
will provide the FAA's Aircraft Certification Office (ACO) with a 
certification plan. The FAA will evaluate the plan to determine if it 
is addressed by current regulations or if special conditions would have 
to be established for the certification. The EFVS will be evaluated in 
an operational context to determine if the system provides an 
equivalent level of safety when in operation compared to the present 
rules. The operator of a foreign-registered aircraft must comply with 
all of the applicable EFVS requirements of this rule.

VIII. Paperwork Reduction Act

    The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires 
that the FAA consider the impact of paperwork and other information 
collection burdens imposed on the public. The FAA has determined that 
there are no new information collection requirements associated with 
this final rule.

IX. International Compatibility

    In keeping with United States obligations under the Convention on 
International Civil Aviation, it is the FAA's policy to comply with 
International Civil Aviation Organization (ICAO) Standards and 
Recommended Practices to the maximum extent practicable. The FAA has 
determined that there are no ICAO Standards and Recommended Practices 
that corresponded to these regulations.

X. Economic Evaluation

    Changes to regulations must undergo several economic analyses. 
First, Executive Order 12866 directs each Federal agency proposing or 
adopting a regulation to only upon a reasoned determination that the 
benefits of the intended regulation justify its costs. Second, the 
Regulatory Flexibility Act of 1980 requires agencies to analyze the 
economic impact of the regulatory changes on small entities. Third, the 
Trade Agreements Act (19 U.S.C. 2531-2533) prohibits agencies from 
setting standards that create unnecessary obstacles to the foreign 
commerce of the United States. In developing U.S. standards, the Trade 
Agreements Act requires agencies to consider international standards 
and, where appropriate, as the basis of U.S. standards. Fourth, the 
Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4) requires agencies 
to prepare a written assessment of the costs, benefits, and other 
effects of proposed or final rules that include a Federal mandate 
likely to result in the expenditure by State, local, or tribal 
governments, in the aggregate, or by the private sector, of $100 
million or more annually (adjusted for inflation).
    In conducting these analyses, FAA has determined that this rule: 
(1) Has benefits that justify its costs, is not a ``significant 
regulatory action'' as defined in section 3(f) of Executive Order 
12866, and is not ``significant'' as defined in DOT's Regulatory 
Policies and Procedures; (2) will not have a significant economic 
impact on a substantial number of small entities; (3) will not create 
barriers to international trade; and (4) does not impose an unfunded 
mandate on state, local, or tribal governments, or on the private 
sector.
    For regulations with an expected minimal impact the above-specified 
analyses are not required. The Department of Transportation Order DOT 
2100.5 prescribes policies and procedures for simplification, analysis, 
and review or regulations. If it is determined that the expected impact 
is so minimal that the proposal does not warrant a full evaluation, a 
statement to that effect and the basis for it is included in proposed 
regulation.
    This rule will allow, but does not require, operators to use an 
enhanced flight vision system on board their

[[Page 1639]]

aircraft. Therefore, this final rule will not impose any cost on any 
operator. As discussed above under ``II. Discussion of the Proposed 
Rule,'' the FAA believes that this final rule will provide operational 
benefits and improve the level of safety.

XI. Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (RFA) establishes ``as a 
principle of regulatory issuance that agencies shall endeavor, 
consistent with the objective of the rule and of applicable statutes, 
to fit regulatory and informational requirements to the scale of the 
business, organizations, and governmental jurisdictions subject to 
regulation.'' To achieve that principle, the RFA requires agencies to 
solicit and consider flexible regulatory proposals and to explain the 
rationale for their actions. The RFA covers a wide-range of small 
entities, including small businesses, not-for-profit organizations and 
small governmental jurisdictions.
    Agencies must perform a review to determine whether a proposed or 
final rule will have a significant impact on a substantial number of 
small entities. If the determination is that it will, the agency must 
prepare a regulatory flexibility analysis as described in the RFA.
    However, if an agency determines that a proposed or final rule is 
not expected to have a significant economic impact on a substantial 
number of small entities, section 605(b) of the RFA provides that the 
head of the agency may so certify and a regulatory flexibility analysis 
is not required. The certification must include a statement providing 
the factual basis for this determination, and the reasoning should be 
clear.
    The FAA certifies that this rule will not have a significant 
economic impact on a substantial number of small entities. This 
rulemaking will allow the operators the option of using an EFVS but the 
use of such a system is not mandated. Therefore, this rulemaking will 
not impose any cost on any operators

XII. International Trade Impact Analysis

    The Trade Agreement Act of 1979 prohibits Federal agencies from 
establishing any standards or engaging in related activities that 
create unnecessary obstacles to the foreign commerce of the United 
States. Legitimate domestic objectives, such as safety, are not 
considered unnecessary obstacles. The statute also requires 
consideration of international standards and, where appropriate, that 
they be the basis for U.S. standards.
    This final rule allows EFVS to be used by foreign as well as U.S. 
operators; therefore, there is a neutral effect on foreign operators. 
In addition, the rule imposes no unnecessary obstacles to the foreign 
commerce of the United States.

XIII. Unfunded Mandates Assessment

    The Unfunded Mandates Reform Act of 1995 (the Act), enacted as Pub. 
L. 104-4 on March 22, 1995 is intended, among other things, to curb the 
practice of imposing unfunded Federal mandates on State, local, and 
tribal governments. Title II of the Act requires each Federal agency to 
prepare a written statement assessing the effects of any Federal 
mandate in a proposed final agency rule that may result in an 
expenditure of $100 million or more expenditure (adjusted annually for 
inflation) in any one year by State, local, and tribal governments, in 
the aggregate, or by the private sector; such a mandate is deemed to be 
a ``significant regulatory action.''
    The final rule does not contain such a mandate. Therefore, the 
requirements of Title II of the Unfunded Mandates Reform Act of 1995 do 
not apply.

XIV. Executive Order 13132, Federalism

    The FAA has analyzed this proposed rule under the principles and 
criteria of Executive Order 13132, Federalism. The FAA has determined 
that this action would not have a substantial direct effect on the 
States, on the relationship between the national government and the 
States, or on the distribution of power and responsibilities among the 
various levels of government. Therefore, we determined that this notice 
does not have federalism implications.

XV. Environmental Analysis

    FAA Order 1050.1D defines FAA action as that may be categorically 
excluded from preparation of a National Environmental Policy Act (NEPA) 
environmental impact statement. In accordance with FAA Order 1050.1D, 
appendix 4, paragraph 4(j), this proposed rulemaking action qualifies 
for a categorical exclusion.

XVI. Energy Impact

    The energy impact of this proposed rule has been assessed in 
accordance with the Energy Policy and Conservation Act (EPCA) (Pub. L. 
94-163, as amended; 42 U.S.C. 6362) and FAA Order 1053.1. The FAA has 
determined that the proposed rule is not a major regulatory action 
under the provisions of the EPCA.

List of Subjects

14 CFR Part 1

    Air transportation.

14 CFR Part 91

    Agriculture, Air traffic control, Aircraft, Airmen, Airports, 
Aviation safety, Freight.

14 CFR Part 121

    Air carriers, Aircraft, Airmen, Aviation safety, Charter Flights, 
Safety, Transportation.

14 CFR Parts 125 and 135

    Aircraft, Airmen, Aviation safety.

The Amendments

0
In consideration of the foregoing, the Federal Administration Aviation 
amends chapter I of 14 CFR as follows:

PART 1--DEFINITIONS AND ABBREVIATIONS

0
1. The authority for part 1 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


0
2. Amend Sec.  1.1 by adding the following definitions in alphabetical 
order to read as follows:


Sec.  1.1  General definitions.

* * * * *
    Enhanced flight visibility (EFV) means the average forward 
horizontal distance, from the cockpit of an aircraft in flight, at 
which prominent topographical objects may be clearly distinguished and 
identified by day or night by a pilot using an enhanced flight vision 
system.
    Enhanced flight vision system (EFVS) means an electronic means to 
provide a display of the forward external scene topography (the natural 
or manmade features of a place or region especially in a way to show 
their relative positions and elevation) through the use of imaging 
sensors, such as a forward looking infrared, millimeter wave 
radiometry, millimeter wave radar, low light level image intensifying.
* * * * *
    Synthetic vision means a computer-generated image of the external 
scene topography from the perspective of the flight deck that is 
derived from aircraft attitude, high-precision navigation solution, and 
database of terrain, obstacles and relevant cultural features.
    Synthetic vision system means an electronic means to display a 
synthetic vision image of the external scene topography to the flight 
crew.
* * * * *

0
3. Amend Sec.  1.2 by adding the following abbreviation in alphabetical 
order to read as follows:

[[Page 1640]]

Sec.  1.2  Abbreviations and symbols.

* * * * *
    EFVS means enhanced flight vision system.
* * * * *

PART 91--GENERAL OPERATING AND FLIGHT RULES

0
4. The authority citation for part 91 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 1155, 40103, 40113, 40120, 44101, 
44111, 44701, 44709, 44711, 44712, 44715, 44716, 44717, 44722, 
46306, 46315, 46316, 46504, 46506-46507, 47122, 47508, 47528-47531, 
articles 12 and 29 of the Convention on International Civil Aviation 
(61 Stat. 1180).


0
5. Amend Sec.  91.175 by revising paragraphs (c) introductory text, 
(d), and (e)(1) introductory text, and by adding paragraphs (l) and (m) 
to read as follows:


Sec.  91.175  Takeoff and landing under IFR.

* * * * *
    (c) Operation below DH or MDA. Except as provided in paragraph (l) 
of this section, where a DH or MDA is applicable, no pilot may operate 
an aircraft, except a military aircraft of the United States, at any 
airport below the authorized MDA or continue an approach below the 
authorized DH unless--
* * * * *
    (d) Landing. No pilot operating an aircraft, except a military 
aircraft of the United States, may land that aircraft when--
    (1) For operations conducted under paragraph (l) of this section, 
the requirements of (l)(4) of this section are not met; or
    (2) For all other part 91 operations and parts 121, 125, 129, and 
135 operations, the flight visibility is less than the visibility 
prescribed in the standard instrument approach procedure being used.
    (e) * * *
    (1) Whenever operating an aircraft pursuant to paragraph (c) or (l) 
of this section and the requirements of that paragraph are not met at 
either of the following times:
* * * * *
    (l) Approach to straight-in landing operations below DH, or MDA 
using an enhanced flight vision system (EFVS). For straight-in 
instrument approach procedures other than Category II or Category III, 
no pilot operating under this section or Sec. Sec.  121.651, 125.381, 
and 135.225 of this chapter may operate an aircraft at any airport 
below the authorized MDA or continue an approach below the authorized 
DH and land unless--
    (1) The aircraft is continuously in a position from which a descent 
to a landing on the intended runway can be made at a normal rate of 
descent using normal maneuvers, and, for operations conducted under 
part 121 or part 135 of this chapter, the descent rate will allow 
touchdown to occur within the touchdown zone of the runway of intended 
landing;
    (2) The pilot determines that the enhanced flight visibility 
observed by use of a certified enhanced flight vision system is not 
less than the visibility prescribed in the standard instrument approach 
procedure being used;
    (3) The following visual references for the intended runway are 
distinctly visible and identifiable to the pilot using the enhanced 
flight vision system:
    (i) The approach light system (if installed); or
    (ii) The following visual references in both paragraphs 
(l)(3)(ii)(A) and (B) of this section:
    (A) The runway threshold, identified by at least one of the 
following:
    (1) The beginning of the runway landing surface;
    (2) The threshold lights; or
    (3) The runway end identifier lights.
    (B) The touchdown zone, identified by at least one of the 
following:
    (1) The runway touchdown zone landing surface;
    (2) The touchdown zone lights;
    (3) The touchdown zone markings; or
    (4) The runway lights.
    (4) At 100 feet above the touchdown zone elevation of the runway of 
intended landing and below that altitude, the flight visibility must be 
sufficient for the following to be distinctly visible and identifiable 
to the pilot without reliance on the enhanced flight vision system to 
continue to a landing:
    (i) The lights or markings of the threshold; or
    (ii) The lights or markings of the touchdown zone;
    (5) The pilot(s) is qualified to use an EFVS as follows--
    (i) For parts 119 and 125 certificate holders, the applicable 
training, testing and qualification provisions of parts 121, 125, and 
135 of this chapter;
    (ii) For foreign persons, in accordance with the requirements of 
the civil aviation authority of the State of the operator; or
    (iii) For persons conducting any other operation, in accordance 
with the applicable currency and proficiency requirements of part 61 of 
this chapter;
    (6) For parts 119 and 125 certificate holders, and part 129 
operations specifications holders, their operations specifications 
authorize use of EFVS; and
    (7) The aircraft is equipped with, and the pilot uses, an enhanced 
flight vision system, the display of which is suitable for maneuvering 
the aircraft and has either an FAA type design approval or, for a 
foreign-registered aircraft, the EFVS complies with all of the EFVS 
requirements of this chapter.
    (m) For purposes of this section, ``enhanced flight vision system'' 
(EFVS) is an installed airborne system comprised of the following 
features and characteristics:
    (1) An electronic means to provide a display of the forward 
external scene topography (the natural or manmade features of a place 
or region especially in a way to show their relative positions and 
elevation) through the use of imaging sensors, such as a forward-
looking infrared, millimeter wave radiometry, millimeter wave radar, 
and low-light level image intensifying;
    (2) The EFVS sensor imagery and aircraft flight symbology (i.e., at 
least airspeed, vertical speed, aircraft attitude, heading, altitude, 
command guidance as appropriate for the approach to be flown, path 
deviation indications, and flight path vector, and flight path angle 
reference cue) are presented on a head-up display, or an equivalent 
display, so that they are clearly visible to the pilot flying in his or 
her normal position and line of vision and looking forward along the 
flight path, to include:
    (i) The displayed EFVS imagery, attitude symbology, flight path 
vector, and flight path angle reference cue, and other cues, which are 
referenced to this imagery and external scene topography, must be 
presented so that they are aligned with and scaled to the external 
view; and
    (ii) The flight path angle reference cue must be displayed with the 
pitch scale, selectable by the pilot to the desired descent angle for 
the approach, and suitable for monitoring the vertical flight path of 
the aircraft on approaches without vertical guidance; and
    (iii) The displayed imagery and aircraft flight symbology do not 
adversely obscure the pilot's outside view or field of view through the 
cockpit window;
    (3) The EFVS includes the display element, sensors, computers and 
power supplies, indications, and controls. It may receive inputs from 
an airborne navigation system or flight guidance system; and
    (4) The display characteristics and dynamics are suitable for 
manual control of the aircraft.

[[Page 1641]]

PART 121--OPERATING REQUIREMENTS: DOMESTIC FLAG, AND SUPPLEMENTAL 
OPERATIONS

0
6. The authority citation for part 121 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 40119, 41706, 44101, 44701-
44702, 44705, 44709-44711, 44713, 44716-44717, 44722, 44901, 44903-
44904, 44912, 46105.


0
7. Amend Sec.  121.651 by revising paragraphs (c) introductory text and 
(d) introductory text to read as follows:


Sec.  121.651  Takeoff and landing weather minimums: IFR: All 
certificate holders.

* * * * *
    (c) If a pilot has begun the final approach segment of an 
instrument approach procedure in accordance with paragraph (b) of this 
section, and after that receives a later weather report indicating 
below-minimum conditions, the pilot may continue the approach to DH or 
MDA. Upon reaching DH or at MDA, and at any time before the missed 
approach point, the pilot may continue the approach below DH or MDA if 
either the requirements of Sec.  91.175(l) of this chapter, or the 
following requirements are met:
* * * * *
    (d) A pilot may begin the final approach segment of an instrument 
approach procedure other than a Category II or Category III procedure 
at an airport when the visibility is less than the visibility minimums 
prescribed for that procedure if that airport is served by an operative 
ILS and an operative PAR, and both are used by the pilot. However, no 
pilot may continue an approach below the authorized DH unless the 
requirements of Sec.  91.175(l) of this chapter, or the following 
requirements are met:
* * * * *

PART 125--CERTIFICATION AND OPERATIONS: AIRPLANES HAVING A SEATING 
CAPACITY OF 20 OR MORE PASSENGERS OR A MAXIMUM PAYLOAD CAPACITY OF 
6,000 POUNDS OR MORE; AND RULES GOVERNING PERSONS ON BOARD SUCH 
AIRCRAFT

0
8. The authority citation for part 125 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44705, 44710-
44711, 44713, 44716-44717, 44722.


0
9. Amend Sec.  125.381 by revising paragraph (c) to read as follows:


Sec.  125.381  Takeoff and landing weather minimums: IFR.

* * * * *
    (c) If a pilot initiates an instrument approach procedure based on 
a weather report that indicates that the specified visibility minimums 
exist and subsequently receives another weather report that indicates 
that conditions are below the minimum requirements, then the pilot may 
continue with the approach only if, the requirements of Sec.  91.175(l) 
of this chapter, or both of the following conditions are met--
    (1) The later weather report is received when the airplane is in 
one of the following approach phases:
    (i) The airplane is on a ILS approach and has passed the final 
approach fix;
    (ii) The airplane is on an ASR or PAR final approach and has been 
turned over to the final approach controller; or
    (iii) The airplane is on a nonprecision final approach and the 
airplane--
    (A) Has passed the appropriate facility or final approach fix; or
    (B) Where a final approach fix is not specified, has completed the 
procedure turn and is established inbound toward the airport on the 
final approach course within the distance prescribed in the procedure; 
and
    (2) The pilot in command finds, on reaching the authorized MDA, or 
DH, that the actual weather conditions are at or above the minimums 
prescribed for the procedure being used.
* * * * *

PART 135--OPERATING REQUIREMENTS: COMMUTER AND ON-DEMAND OPERATIONS

0
10. The authority citation for part 135 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 44113, 44701-44702, 44705, 44709, 
44711-44713, 44715-44717, 44722.


0
11. Amend Sec.  135.225 by revising paragraph (c) to read as follows:


Sec.  135.225  IFR: Takeoff, approach, and landing minimums.

* * * * *
    (c) If a pilot has begun the final approach segment of an 
instrument approach to an airport under paragraph (b) of this section, 
and the pilot receives a later weather report indicating that 
conditions have worsened to below the minimum requirements, then the 
pilot may continue the approach only if the requirements of Sec.  
91.175(l) of this chapter, or both of the following conditions, are 
met--
    (1) The later weather report is received when the aircraft is in 
one of the following approach phases:
    (i) The aircraft is on an ILS final approach and has passed the 
final approach fix;
    (ii) The aircraft is on an ASR or PAR final approach and has been 
turned over to the final approach controller; or
    (iii) The aircraft is on a nonprecision final approach and the 
aircraft--
    (A) Has passed the appropriate facility or final approach fix; or
    (B) Where a final approach fix is not specified, has completed the 
procedure turn and is established inbound toward the airport on the 
final approach course within the distance prescribed in the procedure; 
and
    (2) The pilot in command finds, on reaching the authorized MDA or 
DH, that the actual weather conditions are at or above the minimums 
prescribed for the procedure being used.
* * * * *

    Issued in Washington, DC, on January 5, 2004.
Marion C. Blakey,
Administrator.
[FR Doc. 04-427 Filed 1-6-04; 1:55 pm]
BILLING CODE 4910-13-P