[Federal Register Volume 60, Number 189 (Friday, September 29, 1995)]
[Rules and Regulations]
[Pages 50676-50679]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-24170]




[[Page 50675]]

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Part III





Department of Transportation





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Federal Aviation Administration



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14 CFR Part 91



Notification to Air Traffic Control (ATC) of Deviations From ATC 
Clearances in Response to Traffic Alert and Collision Avoidance System 
Resolution Advisories; Final Rule

  Federal Register / Vol. 60, No. 189 / Friday, September 29, 1995 / 
Rules and Regulations  

[[Page 50676]]


DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 91

[Docket No. 27717; Amdt. No. 91-244]
RIN 2120-AF35


Notification to Air Traffic Control (ATC) of Deviations From ATC 
Clearances in Response to Traffic Alert and Collision Avoidance System 
Resolution Advisories

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: This action codifies the previously announced policy extended 
to pilots during the initial testing of the Traffic Alert and Collision 
Avoidance System (TCAS) during the Limited Implementation Plan for 
TCAS, and during the actual implementation of TCAS under the TCAS 
Transition Plan (TTP). This policy permitted pilots to deviate from an 
air traffic control (ATC) clearance, in non-emergency situations, when 
responding to a TCAS resolution advisory (RA). The language contained 
in current regulations suggests that deviation from an ATC clearance is 
authorized only in an emergency situation. The intended effect of this 
action is to add the TCAS RA as a reason to deviate from a clearance, 
and to require that whenever a pilot deviates from an ATC clearance, 
ATC will be advised as soon as possible.

EFFECTIVE DATE: October 30, 1995.

FOR FURTHER INFORMATION CONTACT:
Mrs. Ellen Crum, Air Traffic Rules Branch, ATP-230, Airspace Rules and 
Aeronautical Information Division, Federal Aviation Administration, 800 
Independence Avenue, SW., Washington, DC 20591; telephone (202) 267-
8783.

SUPPLEMENTARY INFORMATION: 

Background

    On December 26, 1989, the FAA published a petition for rulemaking, 
received from the Air Transport Association of America (ATA), that 
requested the FAA amend section 91.75(a) of the Federal Aviation 
Regulations (FAR) to permit a pilot to deviate from an ATC clearance 
when responding to a TCAS RA (54 FR 52951). (Effective August 18, 1990, 
part 91 of the FAR was revised (54 FR 34284; August 18, 1989) to 
renumber all of its sections. Section 91.75(a) was renumbered as 
section 91.123(a).)
    Section 91.123 of the FAR states, in pertinent part, that each 
pilot in command who, in an emergency, deviates from an ATC clearance 
shall notify ATC of that deviation as soon as possible. The ATA 
petition states that TCAS is an advisory system and not an emergency 
system. The ATA feels that pilots should be able to comply with a TCAS 
RA without exercising emergency authority. The ATA petition mirrors 
current FAA policy and guidance for the use of TCAS II. The petition 
drew no negative comments and one positive comment from the Airline 
Pilots Association (ALPA) that supported the proposal.
    On April 9, 1994, the FAA published a Notice of Proposed Rulemaking 
(59 FR 22142, Notice No. 94-16) that proposed to amend Section 
91.123(a) of the FAR in accordance with the ATA petition. In addition, 
this NPRM proposed to amend Sec. 91.123(c) of the FAR to require pilots 
to notify ATC as soon as possible if they deviate from a clearance in 
response to a RA. The comment period for this NPRM closed on May 31, 
1994 and comments are discussed later in this document.
    Currently, regulations do not provide for any deviation from an ATC 
clearance except in an emergency situation. However, during the initial 
trial and implementation of TCAS II, the FAA notified pilots that no 
enforcement action would be initiated if the pilot deviated from an ATC 
clearance when responding to a TCAS RA. A letter signed by former FAA 
Administrator James B. Busey was published as Appendix C to the TTP 
Project Management Plan, dated August 1, 1990. The FAA also provided 
procedural guidance in Advisory Circular 120-55, ``Air Carrier 
Operational Approval and Use of TCAS II'' dated October 23, 1991, and 
later amended as AC 120-55A dated August 27, 1993. The policy and 
guidance proved successful during the testing and implementation of 
TCAS II.

Related Agency Actions

    On January 10, 1989, the FAA published a final rule (54 FR 940), 
known as the ``TCAS rule,'' that required airplanes having more than 30 
passenger seats and operated under part 121, 125, or 129 to be equipped 
with TCAS II by December 30, 1991. The TCAS rule also required 
airplanes having 10 to 30 passenger seats and operated under part 129 
or 135 to be equipped with TCAS I by February 9, 1995; this compliance 
date was subsequently extended to December 31, 1995 (59 FR 67584, 
December 29, 1994). On April 9, 1990, the FAA amended the TCAS rule by 
revising the schedule for the installation of TCAS II equipment in 
airplanes having more than 30 passenger seats (55 FR 13242). Operators 
of airplanes having more than 30 passenger seats and operated under 
part 121 were required to install TCAS II equipment in accordance with 
a phased-in schedule so that 100% of an operator's covered airplanes 
would be equipped by December 30, 1993. Operations conducted under part 
125 or 129 with airplanes having more than 30 passenger seats were also 
required to install TCAS II equipment by December 30, 1993.

TCAS

    TCAS is airborne equipment that interrogates ATC transponders of 
other aircraft nearby. By computer analysis of the replies, TCAS 
equipment determines which transponder-equipped aircraft are potential 
collision hazards and provides appropriate advisory information to the 
flight crew. If a TCAS-equipped airplane interrogates an aircraft that 
is equipped with a transponder without altitude reporting capability 
(Mode A), range and azimuth information will be provided to the TCAS-
equipped aircraft. If the interrogated aircraft is equipped with an 
altitude encoding transponder (Mode C or Mode S), then relative 
altitude information will be provided in addition to range and azimuth. 
TCAS equipment cannot detect the presence of an aircraft that is not 
equipped with a transponder.
    TCAS equipment performs proximity tests on each detected target. If 
the path of a target is projected to pass within certain horizontal and 
vertical distance criteria, then that target is declared an intruder. 
An intruder that is determined to pose an even greater risk of 
collision is declared a threat. When a threat is declared, TCAS 
equipment will determine the appropriate direction that the TCAS-
equipped aircraft must move (climb or descend) and the vertical rate 
that must be maintained to achieve separation from the threat.
    There are two classes of advisories provided by TCAS equipment. The 
first class, the ``traffic advisory'' (TA), provides supplemental 
information to the pilot that aids in visual detection of other 
aircraft. TA's include the range, bearing, and if the intruder has 
altitude-reporting equipment, the altitude of intruding aircraft 
relative to the TCAS equipped aircraft. TA's without altitude 
information may also be provided from non-altitude reporting 
transponder-equipped intruders. TCAS I equipment provides TA's that 
only assist the pilot in visually detecting an intruder aircraft. The 
second class of advisory, the ``resolution advisory'' (RA), indicates 

[[Page 50677]]
the vertical direction and rate that must be achieved by an aircraft in 
order to prevent insufficient separation. When an RA occurs, the pilot 
flying should respond by direct attention to RA displays and should 
maneuver as indicated unless doing so would jeopardize the safe 
operation of the flight or unless the flight crew has definitive visual 
acquisition of the aircraft causing the RA. TCAS II equipment provides 
both traffic and resolution advisories only in the vertical plane.

The Rule

    This rule accomplishes two things. First, it authorizes deviations 
from an ATC clearance when responding to a TCAS RA. Secondly, it 
requires pilots to notify ATC as soon as possible if they deviate from 
a clearance in response to a TCAS RA. This action codifies existing 
policies and practices that were initiated during the TCAS 
implementation period.

Discussion of Comments

    Interested persons were invited to participate in this rulemaking 
action by submitting written data, views, or arguments. All comments 
received during the comment period were considered before making a 
determination regarding this final rule. The following is a discussion 
of the comments received.
    Five comments were received in response to the NPRM. Of this 
number, three comments were received from associations and two from 
individuals. Most commenters supported amending FAR 91.123(a); however, 
three commenters opposed amending FAR 91.123(c).

I. Compliance With ATC Clearances

    Most commenters support this amendment which allows flight crews to 
deviate from an air traffic control clearance in response to a TCAS RA. 
The Air Transport Association of America (ATA) and the Air Line Pilots 
Association (ALPA) stated that the proposal is fully consistent with 
the ATA petition referenced in the Notice. ATA believes this action 
will remove a potential obstacle to the full use of TCAS by allowing 
flight crews to follow a TCAS RA without pausing to determine if the RA 
maneuver would require the crew to declare an emergency. Another 
commenter states that he believes safety would be improved with this 
amendment, and supports it. The National Air Traffic Controllers 
Association (NATCA) did not comment specifically on this proposed 
change, but offers general comments stating they do not believe the air 
traffic system is as safe today as it was prior to the introduction of 
TCAS.
    On December 30, 1987, the President of the United States signed 
Public Law 100-223 which, among other provisions, amended the FAA Act 
of 1958, Section 601, by adding a new paragraph (f) entitled 
``Collision Avoidance Systems.'' This section requires TCAS II on 
``each civil aircraft of more than 30 seats and which is used to 
provide air transportation of passengers, including intrastate air 
transportation of passengers.'' The amendment does not provide for the 
exception of any class of civil operation or operator, U.S. or foreign, 
from the basic rule. Consequently, the FAA promulgated numerous 
regulations (several of which have been referenced earlier in this 
document) pertaining to TCAS. In addition, the TTP, along with the 
Separation Assurance Task Force (SATF), were established to investigate 
and resolve TCAS related problems in the NAS which are discovered 
during implementation. Participants in this program include the FAA, 
ATA, Regional Airline Association, ALPA, Allied Pilots Association, 
NATCA, Transport Canada, TCAS equipment manufacturers and the major, 
national and regional air carriers.
    The FAA disagrees with NATCA's view that TCAS has compromised 
safety. Since the introduction of TCAS into the NAS, both air traffic 
controllers and flight crews have adjusted their operating procedures. 
With the assistance and cooperation of flight crews and air traffic 
controllers, surveys have been collected and volumes of data analyzed. 
As issues surface, the TTP provides guidance for timely resolution that 
has resulted in better training for both pilots and controllers, the 
issuance of two advisory circulars addressing the use of TCAS, 
amendments to the controllers handbook and the Airman's Information 
Manual (AIM), and updating the TCAS software in order to eliminate 
false and nuisance RA's.
    At the second annual International TCAS Conference held in Reston, 
Virginia in September, 1993, TCAS was lauded by many flight crews as a 
safety enhancing cockpit device.
    For example, TCAS was credited by the captain of a major air 
carrier for saving the lives of nearly 700 people in two B747 aircraft 
traveling over the Pacific Ocean.
    The TCAS Industry Alert Bulletin #5, issued February 18, 1994, 
states that during the prior two years, 16 encounters had occurred 
wherein TCAS II displayed unnecessary resolution advisories that 
directed pilots to cross through each other's altitudes. The RA's were 
unnecessary because the aircraft were safely separated by the ATC 
system. In each of these encounters, the TCAS logic detected the high 
vertical closure rate of the two aircraft and predicted the close 
proximity of the aircraft without knowing that the aircraft intended to 
level off 1000 feet apart in altitude.
    In order to eliminate these unnecessary RA's, a new version of the 
TCAS logic (Version 6.04A) was created and installation required by 12/
31/94. This logic will not generate altitude-crossing RAs when aircraft 
level off within 1000 feet vertically of one another. None of the 16 
encounters previously mentioned would have resulted in altitude-
crossing RAs with the Version 6.04A logic installed.

II. ATC Notification

    ATA and ALPA oppose this proposal which requires flight crews to 
inform ATC as soon as possible when deviating from an ATC clearance in 
response to a TCAS RA. ALPA states they do not oppose notifying ATC of 
any deviation caused by responding to a TCAS RA; however, they believe 
the proposal may imply a sense of urgency for pilots to advise ATC of a 
deviation at a time when complete attention must be focused on 
identifying the intruder and responding to the RA. ALPA states this 
sense of urgency may also be prompted by a concern over possible 
enforcement action should the crew neglect to report the event due to a 
directed frequency change or some other unanticipated event. ATA 
comments that the phrase ``as soon as possible'' implies that 
notification to ATC of a deviation should take place prior to executing 
the maneuver. ATA suggests the word ``practical'' be used in lieu of 
``possible'' which would be consistent with the AIM.
    The FAA does not agree with replacing the word ``possible'' with 
``practical''. The word ``possible'' does not mean that the 
notification has to take place before the pilot has executed the 
appropriate maneuver. ``Possible'' does, however, contain a greater 
urgency than the word ``practical,'' and would require notification to 
ATC of the deviation as soon as the pilot maneuvers the aircraft to a 
safe operating environment. The language is consistent with current 
wording contained in the regulation that requires a flight crew who, in 
an emergency, deviates from an ATC clearance to notify ATC as soon as 
possible. If a pilot deviates from an ATC clearance, the controller 
must be given timely notification of that deviation so that appropriate 
instructions and/or 

[[Page 50678]]
advisories can be issued to ensure a safe, orderly, and expeditious 
flow of traffic. By advising ATC as soon as possible that an RA has 
been received, the controller can evaluate the situation, determine the 
most appropriate and safe course of action, and issue alternate 
instructions if necessary.
    ALPA states that the requirement to report a deviation from an ATC 
clearance as a result of an RA is stated in the Airman's Information 
Manual (AIM), FAA Advisory Circular 120-55, and each TCAS equipped 
aircraft flight operations manual. Consequently, the commenter believes 
this proposal is redundant and unnecessary.
    The FAA acknowledges there are several FAA publications which 
explain and encourage pilots to communicate with ATC when deviating 
from a clearance upon receipt of a RA. However, the FAA has determined 
that safety within the NAS can only be maintained if pilots are 
required to advise controllers when a deviation from an ATC clearance 
has occurred as a result of an RA.
    NATCA opposes this rule change due to concerns for the safety of 
persons operating in the NAS. However, NATCA does not provide specific 
instances of how or where safety is compromised, but merely reiterates 
their ongoing concern with the TCAS program.
    The FAA has determined that pilot notification of a deviation from 
a clearance due to a TCAS RA enhances safety in the NAS. Air traffic 
controllers base their control and traffic management decisions on the 
expectation that pilots will comply with ATC-assigned routes, 
altitudes, and other clearances. If a pilot deviates from an ATC 
clearance, the controller must be given timely notification of that 
deviation so that appropriate instructions and/or advisories can be 
issued to ensure a safe, orderly, and expeditious flow of traffic. By 
advising ATC as soon as possible that an RA has been received, the 
controller can evaluate the situation, determine the most appropriate 
and safe course of action, and issue alternate instructions if 
necessary.

III. Resolution Advisory Maneuver--An Emergency?

    One commenter contends that any deviation from an ATC clearance is 
an emergency; therefore, this rule change is not needed. The commenter 
believes the cause of the deviation need not be an emergency, but the 
mere fact that an aircraft is not following an ATC clearance should be 
considered an emergency. The commenter suggested the phrase ``in an 
emergency'' be deleted from the rule; thereby, any time an aircraft 
deviates from an ATC clearance, regardless of the reason, ATC will be 
notified.
    The FAA disagrees that an RA maneuver is an emergency action. TCAS 
is designed to serve as a backup (safety net) to visual collision 
avoidance, application of ``right of way rules'', and air traffic 
separation services. Since its inception, TCAS has been considered by 
the FAA and industry to be a supplement to the ATC system that provides 
flight guidance to ensure adequate separation from other aircraft. 
Additionally, although the suggestion to remove the word ``emergency'' 
from the language of the regulations is outside the scope of this 
rulemaking, the FAA will consider the merits of the comment for 
possible future rulemaking.

Regulatory Evaluation Summary

    Executive Order 12866 established the requirement that, within the 
extent permitted by law, a Federal regulatory action may be undertaken 
only if the potential benefits to society for the regulation outweigh 
the potential costs to society. In response to this requirement, and in 
accordance with Department of Transportation policies and procedures, 
the FAA has estimated the anticipated benefits and costs of this 
rulemaking action. The results are stated in this section. The FAA has 
determined that this rule change is not a ``significant rulemaking 
action,'' as defined by Executive Order 12866 (Regulatory Planning and 
Review).
    The FAA has determined that this rule will be cost-beneficial 
because it imposes no costs and would promote air safety. There will 
not be any changes in notification or reporting requirements for 
deviations from ATC clearances that are necessary to avoid potential 
collision hazards. This action codifies a previously announced policy 
that pilots who deviate from their assigned altitudes in response to a 
TCAS RA will provide timely notice, as soon as possible, to air traffic 
control. Such non-written, voice notification will give controllers an 
opportunity to resolve any conflicts resulting from a TCAS II-equipped 
aircraft being at other than the assigned altitude.

International Trade Impact Statement

    This action will not impose a competitive disadvantage to either 
U.S. air carriers doing business abroad or foreign air carriers doing 
business in the United States. This assessment is based on the fact 
that this rule will not impose additional costs on either U.S. or 
foreign air carriers.

Regulatory Flexibility Determination

    In accordance with the Regulatory Flexibility Act of 1980, the FAA 
has determined that this action will not have a significant economic 
impact, positive or negative, on a substantial number of small 
entities. This assessment is based on the fact action will not impose 
any additional cost on aircraft operators.

Paperwork Reduction Act

    There are no requirements for information collection associated 
with this action that would require approval from the Office of 
Management and Budget pursuant to the Paperwork Reduction Act of 1980 
(Pub. L. 96-511).

Federalism Implications

    This regulation will not have substantial direct effects 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, in accordance with Executive 
Order 12612, it is determined that this rule does not have sufficient 
federalism implications to warrant the preparation of a Federalism 
Assessment.

International Civil Aviation Organization and Joint Aviation 
Regulations

    In keeping with the U.S. obligations under the Convention on 
International Civil Aviation (ICAO), it is FAA policy to comply with 
ICAO Standards and Recommended Practices (SARP) to the maximum extent 
practicable. The FAA has determined that this action complies with the 
ICAO SARP.

Conclusion

    For the reasons discussed in the preamble, and based on the 
findings in the Regulatory Flexibility Determination and the 
International Trade Impact Analysis, the FAA has determined that this 
regulation is not a ``significant regulatory action'' under Executive 
Order 12866. This regulation is not considered significant under DOT 
Order 2100.5, Policies and Procedures (44 FR 11034; February 26, 1979). 
In addition, the FAA certifies that this regulation will not have a 
significant economic impact, positive or negative, on a substantial 
number of small entities under the criteria of the Regulatory 
Flexibility Act.

List of Subjects in 14 CFR Part 91

    Air traffic control, Aircraft, Aviation safety.

[[Page 50679]]


The Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration amends part 91 of the Federal Aviation Regulations (14 
CFR part 91) as follows:

PART 91--GENERAL OPERATING AND FLIGHT RULES

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

    Authority: 42 U.S.C. 4321 et seq.; 49 U.S.C. app. 1301, 1303, 
1344, 1348, 1352 through 1355, 1401, 1421 through 1431, 1471, 1472, 
1502, 1510, 1522, and 2121 through 2125, 2157, 2158; 49 U.S.C. 
106(g); articles 12, 29, 31, and 32(a) of the Convention on 
International Civil Aviation (61 Stat. 1180); E.O. 11514, 35 FR 
4247, 3 CFR, 1966-1970 Comp., p. 902.

    2. Section 91.123 is amended by revising paragraphs (a) and (c) to 
read as follows:


Sec. 91.123  Compliance with ATC clearances and instructions.

    (a) When an ATC clearance has been obtained, no pilot in command 
may deviate from that clearance unless an amended clearance is 
obtained, an emergency exists, or the deviation is in response to a 
traffic alert and collision avoidance system resolution advisory. 
However, except in Class A airspace, a pilot may cancel an IFR flight 
plan if the operation is being conducted in VFR weather conditions. 
When a pilot is uncertain of an ATC clearance, that pilot shall 
immediately request clarification from ATC.
* * * * *
    (c) Each pilot in command who, in an emergency, or in response to a 
traffic alert and collision avoidance system resolution advisory, 
deviates from an ATC clearance or instruction shall notify ATC of that 
deviation as soon as possible.
* * * * *
    Issued in Washington, D.C. on September 13, 1995.
David R. Hinson,
Administrator.
[FR Doc. 95-24170 Filed 9-28-95; 8:45 am]
BILLING CODE 4910-13-M