[Federal Register Volume 62, Number 19 (Wednesday, January 29, 1997)]
[Rules and Regulations]
[Pages 4134-4137]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-2243]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 27

[Docket No. 97-ASW-1; Special Condition 27-ASW-4]


Special Condition: McDonnell Douglas Helicopter Systems Model MD-
600N Helicopter

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special condition; request for comments.

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SUMMARY: This special condition is issued for McDonnell Douglas 
Helicopter Systems (MDHS) Model MD-600N helicopter. This helicopter 
will have a novel or unusual design feature associated with the Full 
Authority Digital Engine Control (FADEC). The applicable airworthiness 
regulations do not contain appropriate safety standards to protect 
systems that perform critical functions from the effects of high-
intensity radiated fields (HIRF). This special condition contains 
additional

[[Page 4135]]

safety standards that the Administrator considers necessary to ensure 
that critical functions of systems will be maintained when exposed to 
HIRF.

DATES: Effective January 29, 1997. Comments for inclusion in the Rules 
Docket must be received by April 29, 1997.

ADDRESSES: Comments may be mailed in duplicate to the Federal Aviation 
Administration (FAA), Office of the Assistant Chief Counsel, Attn: 
Rules Docket No. 97-ASW-1, Fort Worth, Texas 76193-0007, or delivered 
in duplicate to the Office of the Assistant Chief Counsel, 2601 Meacham 
Blvd., Fort Worth, Texas 76137. Comments must be marked Docket No. 97-
ASW-1. Comments may be inspected in the Rules Docket weekdays, except 
Federal holidays, between 9 a.m. and 3 p.m.

FOR FURTHER INFORMATION CONTACT: Robert McCallister, FAA, Rotorcraft 
Standards Staff, Regulations Group, Fort Worth, Texas 76193-0110; 
telephone (817) 624-5121.

SUPPLEMENTARY INFORMATION: The FAA has determined that notice and 
opportunity for prior public comment hereon are impracticable because 
these procedures would significantly further delay issuance of the 
approval design and thus delay delivery of the affected helicopter. 
Reaching agreement on the certification basis has delayed issuance of 
this special condition. These notice and comment procedures are also 
considered unnecessary since the public has been previously provided 
with a substantial number of opportunities to comment on substantially 
identical special conditions, and their comments have been fully 
considered. Therefore, good cause exists for making this special 
condition effective upon issuance.

Comments Invited

    Although this final special condition was not subject to notice and 
opportunity for prior public comment, comments are invited on this 
final special condition. Interested persons are invited to comment by 
submitting such written data, views, or arguments as they may desire. 
Communications should identify the regulatory docket number and be 
submitted in duplicate to the address specified under the caption 
addresses. All communications received on or before the closing date 
for comments will be considered. This special condition may be changed 
in light of comments received. All comments received will be available 
in the Rules Docket for examination by interested persons, both before 
and after the closing date for comments. A report summarizing each 
substantive public contact with FAA personnel concerning this 
rulemaking will be filed in the docket. Persons wishing the FAA to 
acknowledge receipt of their comments submitted in response to this 
special condition must submit a self-addressed, stamped postcard on 
which the following statement is made: ``Comments to Docket No. 97-ASW-
1.'' The postcard will be date and time stamped and returned to the 
commenter.

Background

    On April 7, 1995, MDHS, located in Mesa, Arizona, made application 
to the FAA to amend Type Certificate (TC) H3WE to include the Model MD-
600N helicopter.

Type Certification Basis

    Based upon the criteria of 14 CFR part 21 (part 21), Subpart B, 
Sec. 21.19, the FAA will approve design of the MD-600N model helicopter 
as an amendment to TC H3WE, and a new TC will not be required. The 
certification basis for the MD-600N will be part 27, as amended by 
Amendments 27-1 through 27-30, except as more specifically stated as 
follows:

Section 27.561 as amended through Amendment 24
Section 27.562 as amended through Amendment 25
Section 27.607 as amended through Amendment 3
Section 27.785 as amended through Amendment 20
Section 27.863 as amended through Amendment 16
Section 27.1325 as amended through Amendment 12

    The Model MD-600N will use digital electronics in systems such as 
the FADEC, which make the rotorcraft vulnerable to HIRF. The existing 
airworthiness regulations do not contain adequate or appropriate safety 
standards for the protection of these systems from the effects of HIRF 
external to the helicopter; therefore, a special condition is required; 
reference FAA Policy Memorandums dated December 5, 1989, January 30, 
1990, March 8, 1991, and July 29, 1992.
    Special conditions may be issued and amended, as necessary, as a 
part of the type certification basis if the Administrator finds that 
the airworthiness standards designated in accordance with 
Sec. 21.101(b)(2) do not contain adequate or appropriate safety 
standards because of novel or unusual design features of an aircraft or 
installation. Special conditions, as appropriate, are issued in 
accordance with Sec. 11.49 and will become a part of the type 
certification basis, as provided by Sec. 21.101(b)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should the applicant apply for a supplemental type 
certificate (STC) to modify any other model included on the same TC to 
incorporate the same novel or unusual design feature, the special 
conditions would also apply to the other model under the provisions of 
Sec. 21.101(a)(1).

Discussion

    The MDHS Model MD-600N, at the time of application, incorporated 
one and possibly more electrical/electronic systems, such as FADEC, 
that will be performing functions critical to the continued safe flight 
and landing of the helicopter. FADEC is an electronic device that 
performs the functions of engine control during visual flight rules 
(VFR) and instrument flight rules (IFR) operations in instrument 
meteorological conditions. After the MD-600N design is finalized, MDHS 
will provide the FAA with a hazard analysis that will identify any 
other critical functions, required for continued safe flight and 
landing, performed by the electrical/electronic systems.
    Recent advances in technology have given rise to the application in 
aircraft designs of advanced electrical and electronic systems that 
perform critical functions. These advanced systems are responsive to 
the transient effects of induced electrical current and voltage caused 
by HIRF incident on the external surface of the helicopter. These 
induced transient currents and voltages can degrade the performance of 
the electrical/electronic systems by damaging the components or by 
upsetting the systems' functions.
    Furthermore, the electromagnetic environment has undergone a 
transformation not envisioned by the current application of the Sec.  
27.1309(a) requirement. Higher energy levels radiate from operational 
transmitters that are currently used for radar, radio, and television. 
Also, the number of transmitters has increased significantly.
    Existing aircraft certification requirements are inappropriate in 
view of these technological advances. In addition, the FAA has received 
reports of some significant safety incidents and accidents involving 
military aircraft equipped with advanced electronic systems when they 
were exposed to electromagnetic radiation.
    The combined effects of the technological advances in helicopter 
design and the changing environment have resulted in an increased level 
of vulnerability of the electrical/electronic

[[Page 4136]]

systems required for the continued safe flight and landing of the 
helicopter. Effective measures to protect these helicopters against the 
adverse effects of exposure to HIRF will be provided by the design and 
installation of these systems. The following primary factors 
contributed to the current conditions: (1) increased use of sensitive 
electronics that perform critical functions, (2) reduced 
electromagnetic shielding afforded helicopter systems by advanced 
technology airframe materials; (3) adverse service experience of 
military aircraft using these technologies, and (4) an increase in the 
number and power of radio frequency emitters and the expected increase 
in the future.
    The FAA recognizes the need for aircraft certification standards to 
keep pace with the developments in technology and environment and, in 
1986, initiated a high priority program to (1) determine and define the 
electromagnetic energy levels; (2) develop and describe guidance 
material for design, test, and analysis; and (3) prescribe and 
promulgate regulatory standards.
    The FAA participated with industry and airworthiness authorities of 
other countries to develop internationally recognized standards for 
certification.
    The FAA and airworthiness authorities of other countries have 
identified a level of HIRF environment that a helicopter could be 
exposed to during IFR operations. While the HIRF requirements are being 
finalized, the FAA is adopting special conditions for the certification 
of aircraft that employ electrical/electronic systems performing 
critical functions. The accepted maximum energy levels that civilian 
helicopter system installations must withstand for safe operations are 
based on surveys and analysis of existing radio frequency emitters. 
These external threat levels are believed to represent the worst-case 
exposure for a helicopter operating under IFR.
    The specified HIRF environment is based on many critical 
assumptions. With the exception of takeoff and landing at an airport, 
one of these assumptions is that the aircraft would be not less than 
500 feet above ground level (AGL). Helicopters operating under visual 
flight rules (VFR) routinely operate at less than 500 feet AGL and 
perform takeoffs and landings at locations other than controlled 
airports. Therefore, it would be expected that the HIRF environment 
experienced by a helicopter operating VFR may exceed the defined 
environment by 100 percent or more.
    This special condition will require the systems that perform 
critical functions, as installed in aircraft, to meet certain standards 
based on either a defined HIRF environment or a fixed value using 
laboratory tests.
    The applicant may demonstrate that the operation and operational 
capabilities of the installed electrical/electronic systems that 
perform critical functions are not adversely affected when the aircraft 
is exposed to the HIRF environment. The FAA has determined that the 
environment defined in Table I is acceptable for critical functions in 
helicopters operating at or above 500 feet AGL. For critical functions 
in helicopters operating at altitudes less than 500 feet AGL, 
additional considerations must be given.The applicant may demonstrate 
by a laboratory test that the electrical/electronic systems that 
perform critical functions withstand a peak electromagnetic field 
strength in a frequency range of 10 KHZ to 18 GHZ. If a 
laboratory test is used to show compliance with the HIRF requirements, 
no credit would be given for signal attenuation due to installation. A 
level of 100 v/m and further considerations, such as an alternate 
technology backup that is immune to HIRF, are appropriate for critical 
functions during IFR operations. A level of 200 v/m and further 
considerations, such as an alternate technology backup that is immune 
to HIRF, are more appropriate for critical functions during VFR 
operations.
    For helicopters, the primary electronic flight displays are 
critical for IFR operations and a FADEC is an example of a critical 
functioning system for all operations (both IFR and VFR).
    A preliminary hazard analysis must be performed by the applicant 
for approval by the FAA to identify electrical/electronic systems that 
perform critical functions. The term ``critical'' means those functions 
whose failure would contribute to or cause a failure condition that 
would prevent the continued safe flight and landing of the helicopter. 
The systems identified by the hazard analysis that perform critical 
functions are the ones that are required to have HIRF protection.
    A system may perform both critical and noncritical functions. 
Primary electronic flight display systems and their associated 
components perform critical functions such as attitude, altitude, and 
airspeed indication. HIRF requirements would only apply to the critical 
functions.
    Compliance with HIRF requirements will be demonstrated by tests, 
analysis, models, similarity with existing systems, or a combination of 
these methods. Service experience alone will not be acceptable since 
such experience in normal flight operations may not include an exposure 
to the HIRF environmental condition. Reliance on a system with similar 
design features for redundancy as a means of protection against the 
effects of external HIRF is generally insufficient since all elements 
of a redundant system are likely to be concurrently exposed to the 
fields.
    The modulation should be selected for the signal most likely to 
disrupt the operation of the system under test, based on its design 
characteristics. For example, flight control systems may be susceptible 
to 3 HZ square wave modulation while the video signals for 
electronic display systems may be susceptible to 400 HZ sinusoidal 
modulation. If the worst-case modulation is unknown or cannot be 
determined, default modulations may be used. Suggested default values 
are a 1 KHZ sine wave with 80 percent depth of modulation in the 
frequency range from 10 KHZ to 400 MHZ and 1 KHZ square 
wave with greater than 90 percent depth of modulation from 400 MHZ 
to 18 GHZ. For frequencies where the unmodulated signal would 
cause deviations from normal operation, several different modulating 
signals with various waveforms and frequencies should be applied.
    Acceptable system performance would be attained by demonstrating 
that the critical function components of the system under consideration 
continue to perform their intended function during and after exposure 
to required electromagnetic fields. Deviations from system 
specification may be acceptable but must be independently assessed by 
the FAA on a case-by-case basis.

                  Table 1.--Field Strength Volts/meter                  
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                      Frequency                         Peak     Average
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10-100 KHZ..........................................        50        50
100-500.............................................        60        60
500-2000............................................        70        70
2-30 MHZ............................................       200       200
30-100..............................................        30        30
100-200.............................................       150        33
200-400.............................................        70        70
400-700.............................................      4020       935
700-1000............................................      1700       170
1-2 GHZ.............................................      5000       990
2-4.................................................      6680       840
4-6.................................................      6850       310
6-8.................................................      3600       670
8-12................................................      3500      1270
12-18...............................................      3500       360
18-40...............................................      2100       750
------------------------------------------------------------------------

    As discussed above, this special condition would be applicable to 
the

[[Page 4137]]

Model MD600N helicopter, modified by MDHS. Should MDHS apply at a later 
date for a STC to modify any other model on TC H3WE to incorporate the 
same novel or unusual design feature, the special conditions would 
apply to that model as well, under the provisions of Sec. 21.101(a)(1).

Conclusion

    This action affects only certain unusual or novel design features 
on one series of helicopters. It is not a rule of general applicability 
and will affect only the manufacturer who applied to the FAA for 
approval of these features on the affected helicopters.
    The substance of this special condition has been subjected to the 
notice and comment procedure in several prior special conditions and 
has been finalized without substantive change. It is unlikely that 
prior public comment would result in a significant change in the 
substance contained herein. For this reason, and because a delay would 
significantly affect the certification of the helicopters, which is 
imminent, the FAA has determined that prior public notice and comment 
are unnecessary and impracticable, and good cause exists for adopting 
this special condition immediately. Therefore, this special condition 
is being made effective upon issuance. The FAA is requesting comments 
to allow interested persons to submit views that may not have been 
submitted in response to prior opportunities for comment.

List of Subjects in 14 CFR Parts 21 and 27

    Aircraft, Air transportation, Aviation safety, Rotorcraft, Safety.

    The authority citation for this special condition is as follows:

    Authority: 49 U.S.C. 1344, 1348(c), 1352, 1354(a), 1355, 1421 
through 1431, 1502, 1651(b)(2); 42 U.S.C. 1857f-10, 4321 et seq.: 
E.O. 11541; 49 U.S.C. 106(g).

The Final Special Condition

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special condition is issued as part of the 
supplemental type certification bases for the McDonnell Douglas 
Helicopter Systems Model MD-600N helicopter.

Protection for Electrical/Electronic Systems From High Intensity 
Radiated Fields

    Each system that performs critical functions must be designed and 
installed to ensure that the operation and operational capabilities of 
these critical functions are not adversely affected when the helicopter 
is exposed to high intensity radiated fields external to the 
helicopter.

    Issued in Fort Worth, Texas, on January 21, 1997.
Eric Bries,
Acting Manager, Rotorcraft Directorate Aircraft Certification Service.
[FR Doc. 97-2243 Filed 1-28-97; 8:45 am]
BILLING CODE 4910-13-P