Special Condition: Eurocopter Deutschland Model MBB-BK 117 C-1 Helicopter, Electronic Flight Instrument System

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 29

[Docket No. 94-ASW-2; Special Condition 29-ASW-14]

Special Condition: Eurocopter Deutschland Model MBB-BK 117 C-1

Helicopter, Electronic Flight Instrument System

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special condition; request for comments.

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SUMMARY: This special condition is issued for the Eurocopter

Deutschland Model MBB-BK 117 C-1 helicopter modified by Omniflight

Helicopter. This helicopter will have a novel or unusual design feature

associated with the Electronic Flight Instrument System. The applicable

airworthiness regulations do not contain adequate or appropriate safety

standards for the protection of these critical function systems from

the effects of external high intensity radiated fields (HIRF). This

special condition contains additional safety standards that the

Administrator considers necessary to establish a level of safety

equivalent to that provided by the applicable airworthiness standards.

DATES: The effective date of this special condition is September 23,

1994. Comments must be received on or before November 22, 1994.

ADDRESSES: Comments may be mailed in duplicate to: Federal Aviation

Administration (FAA), Office of the Assistant Chief Counsel, Attn:

Rules Docket No. 94-ASW-2, Fort Worth, Texas 76193-0007, or delivered

in duplicate to the Office of the Assistant Chief Counsel, 2601 Meacham

Blvd., Room 663, Fort Worth, Texas 76137. Comments must be marked

Docket No. 94-ASW-2. Comments may be inspected in the Rules Docket

weekdays, except Federal holidays, between 9 a.m. and 3 p.m.

FOR FURTHER INFORMATION CONTACT:Mr. Robert McCallister, FAA, Rotorcraft

Directorate, Policy and Procedures Group, Fort Worth, Texas 76193-0112;

telephone (817) 222-5121.

SUPPLEMENTARY INFORMATION: The FAA has determined that notice and

opportunity for prior public comment hereon are impracticable because

these procedures would significantly delay issuance of the approval

design and thus delay delivery of the affected helicopter. 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 on

this final special condition 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 notice must submit with those comments a

self-addressed, stamped postcard on which the following statement is

made: ``Comments to Docket No. 94-ASW-2.'' The postcard will be date

and time stamped and returned to the commenter.

Background

On May 6, 1994, Omniflight Helicopter, Dallas, Texas, applied for a

Supplemental Type Certificate for installation of an Electronic Flight

Instrument System in a Eurocopter Deutschland Model MBB-BK 117 C-1

helicopter. This is a 7 (10 with approved kit) passenger, twin engine,

7,385 pound transport category helicopter.

Type Certification Basis

The certification basis established for the Eurocopter Deutschland

Model MBB-BK 117 C-1 helicopter includes: 14 CFR 21.29 and 14 CFR part

29 effective February 1, 1965, Amendments 29-1 through 29-16; in

addition, the Airworthiness Criteria for helicopter instrument flight

rules (IFR) certification dated December 15, 1978, and Equivalent

Safety Findings for Federal Aviation Regulations (FAR) Secs. 29.175(b),

29.811(h)(i), and 29.1151(b).

If the Administrator finds that the applicable airworthiness

regulations do not contain adequate or appropriate safety standards for

this helicopter because of a novel or unusual design feature, special

conditions are prescribed under the provisions of 14 CFR 21.16 to

establish a level of safety equivalent to that established in the

regulations.

Special conditions, as appropriate, are issued in accordance with

14 CFR 11.49 and become part of the type certification basis in

accordance with 14 CFR 21.101(b)(2). Provision is made for the public

comment period in 14 CFR 11.28.

Discussion

The Eurocopter Deutschland Model MBB-BK 117 C-1 helicopter, at the

time of the application for modification by OmniFlight Helicopter, was

identified as having modifications that incorporate one and possibly

more electrical, electronic, or combination of electrical and

electronic (electrical/electronic) systems that will perform functions

critical to the continued safe flight and landing of the helicopters.

The electronic flight instrument system performs the attitude display

function. The display of attitude, altitude, and airspeed is critical

to the continued safe flight and landing of the helicopters for IFR

operations in instrument meteorological conditions. After the design is

finalized, Eurocopter Deutschland will provide the FAA with a

preliminary hazard analysis that will identify any other critical

functions performed by the electrical/electronic systems that are

critical to the continued safe flight and landing of the helicopters.

Recent advances in technology have prompted the design of aircraft

that include advanced electrical and electronic systems that perform

functions required for continued safe flight and landing. However,

these advanced systems respond to the transient effects of induced

electrical current and voltage caused by the high intensity radiated

fields (HIRF) incident on the external surface of the helicopters.

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 FAR

Sec. 29.1309(a). Higher energy levels radiate from operational

transmitters currently used for radar, radio, and television; and 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 electrical/electronic systems

when they were exposed to electromagnetic radiation.

The combined effects of technological advances in helicopter design

and the changing environment have resulted in an increased level of

vulnerability of the electrical and electronic systems required for the

continued safe flight and landing of the helicopters. 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 technological developments and a changing environment

and in 1986 initiated a high priority program to: (1) Determine and

define electromagnetic energy levels; (2) develop 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 a special condition for the

certification of aircraft that employ electrical/electronic systems

that perform critical functions. The accepted maximum energy levels

that civilian helicopter system installations must withstand for safe

operation are based on surveys and analysis of existing radio frequency

emitters. This special condition will require the helicopters'

electrical/electronic systems and associated wiring to be protected

from these energy levels. These external threat levels are believed to

represent the worst-case exposure for a helicopter operating under IFR.

The HIRF environment specified in this special condition 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 the 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 defined HIRF environment. The FAA has determined that

the environment defined in Table 1 is acceptable for critical functions

in helicopters operating at or above 500 feet AGL. For critical

functions of helicopters operating at less than 500 feet AGL,

additional factors must be considered.

The applicant may also demonstrate by a laboratory test that the

electrical/electronic systems that perform critical functions can

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 defined HIRF environment, no credit will be given

for signal attenuation due to installation. A level of 100 volts per

meter (v/m) and other 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. Applicants

must perform a preliminary hazard analysis 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 helicopters. The systems identified by the hazard

analysis as performing critical functions 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 indications. HIRF requirements would apply only to the systems

that perform critical functions.

Compliance with HIRF requirements will be demonstrated by tests,

analysis, models, similarity with existing systems, or a combination of

these methods. The two basic options of either testing the rotorcraft

to the defined environment or laboratory testing may not be combined.

The laboratory test allows some frequency areas to be under tested and

requires other areas to have some safety margin when compared to the

defined environment. The areas required to have some safety margin are

those shown, by past testing, to exhibit greater susceptibility to

adverse effects from HIRF; and laboratory tests, in general, do not

accurately represent the aircraft installation. Service experience

alone will not be acceptable since such experience in normal flight

operations may not include an exposure to HIRF. Reliance on a system

with similar design features for redundancy, as a means of protection

against the effects of external HIRF, is generally insufficient because

all elements of a redundant system are likely to be concurrently

exposed to the radiated fields.

The modulation that represents the signal most likely to disrupt

the operation of the system under test, based on its design

characteristics, should be selected. 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

specifications 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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Conclusion

This action affects only certain unusual or novel design features

on one model of helicopter. It is not a rule of general applicability

and affects only the applicant who applied to the FAA for approval of

these features on the affected helicopter.

The substance of this special condition for similar installations

in a variety of helicopters has been subjected to the notice and

comment procedure and has been finalized without substantive change. It

is unlikely that prior public comment would result in a significant

change from the substance contained herein. For this reason, and

because a delay would significantly affect the certification of the

helicopter, which is imminent, the FAA has determined that prior public

notice and comment are unnecessary and impractical, 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 Part 29

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

The authority citations for this special condition are 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. 11514; 49 U.S.C. 106(g).

The Special Condition

Accordingly, pursuant to the authority delegated to me by the

Administrator, the following special condition is issued as part of the

type certification basis for the Eurocopter Deutschland Model MBB-BK

117 C-1 helicopter:

Protection for Electrical and 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 September 13, 1994.

A.J. Merrill,

Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.

[FR Doc. 94-23568 Filed 9-22-94; 8:45 am]

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