[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
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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