Special Condition: Bell Helicopter Textron Model 222U Helicopter, Electronic Flight Instrument System

SUMMARY: This notice proposes a special condition for the Bell

Helicopter Textron, Inc., Model 222U helicopter modified by Heli-Dyne

Systems, Inc. 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 safety

standards for the protection of these critical function systems from

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

notice contains the additional safety standards that the Administrator

considers necessary to establish a level of safety equivalent to that

established by the airworthiness standards of part 29 of the Federal

Aviation Regulations.

DATES: Comments must be received on or before January 26, 1995.

ADDRESSES: Comments on this proposal may be mailed in duplicate to:

Federal Aviation Administration (FAA), Office of the Assistant Chief

Counsel, Attn: Rules Docket No. 94-ASW-3, Fort Worth, Texas 76193-0007,

or delivered in duplicate to the Office of the Assistant Chief Counsel,

2601 Meacham Blvd., Fort Worth, Texas. Comments must be marked Docket

No. 94-ASW-3. 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:

Comments Invited

Interested persons are invited to participate in the making of this

proposed 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 above. All communications received on or before the closing

date for comments will be considered before taking action on this

proposal. The special condition proposed in this notice 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-3.'' The postcard will be date and time stamped and returned

to the commenter.

Background

On May 16, 1994, Heli-Dyne Systems, Inc., Hurst, Texas, applied for

a Supplemental Type Certificate for installation of an Electronic

Flight Instrument System in the Bell Helicopter Textron (BHTI) Model

222U helicopter. This model helicopter is a 10 passenger, 2 engine,

8,250 pound (Category B) or 7,850 pound (Category A) transport category

helicopter.

Type Certification Basis

The certification basis established for the BHTI Model 22U

helicopter includes: 14 CFR 21.29 and part 29 of the Federal Aviation

Regulations (FAR) effective February 1, 1965 (Transport Categories A

and B), Amendments 29-1 through 29-9; Amendment 29-11; Sec. 29.997 of

Amendment 29-10; Sec. 29.927(b)(2) of Amendment 29-17; Secs. 29.801,

29.25(c) 29.865, 29.1557(c), and 29.1555(c) of Amendment 29.12;

Secs. 29.1, 29.79, 29.1517, and 29.1587 of Amendment 29-21; Criteria

for Helicopter Instrument Flight Rule (IFR) certification dated

December 15, 1978; Exemption No. 2789, Sec. 29.811(h)(1) (following

Amendment 24, effective December 6, 1984, Sec. 29.811(h)(1) became

Sec. 29.811(f)(2)); and Exemption No. 4395, Sec. 29.855(a) and portions

of Sec. 29.855(d).

If the Administration finds that the applicable airworthiness

regulations do not contain adequate or appropriate safety standards for

these helicopters because of a novel or unusual design feature, special

conditions are prescribed under the provisions of Sec. 21.16 to

establish a level of safety equivalent to that established in the

regulations.

Special conditions, as appropriate, are issued in accordance with

Sec. 11.49 of the FAR after public notice, as required by Secs. 11.28

and 11.29(b), and become part of the type certification basis in

accordance with Sec. 21.101(b)(2).

Discussion

The BHTI Model 222U helicopter, at the time of the application for

modification by Heli-Dyne Systems, Inc., was identified as

incorporating 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, Heli-Dyne

Systems, Inc., will provide the FAA with a preliminary hazard 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

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

transmitters currently used for radar, radio, and television; 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 of 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 proposed special condition

is based on many critical assumptions. With the exception of takeoff

and landing at an airport, one of these assumptions is 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

capability 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 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 that have been, by past testing, shown 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

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

Frequency Peak Average

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

10-100 KH2.......................................... 50 50

100-500............................................. 60 60

500-2,000........................................... 70 70

2-30 MH2............................................ 200 200

30-100.............................................. 30 30

100-200............................................. 150 33

200-400............................................. 70 70

400-700............................................. 4,020 935

700-1,000........................................... 1,700 170

1-2 GH2............................................. 5,000 990

2-4................................................. 6,680 840

4-6................................................. 6,850 310

6-8................................................. 3,600 670

8-12................................................ 3,500 1,270

12-18............................................... 3,500 360

18-40............................................... 2,100 750

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

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 helicopters.

List of Subjects in 14 CFR Parts 21 and 29

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. 11514; 49 U.S.C. 106(g).

The Proposed Special Condition

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration (FAA) proposes the

following special condition as a part of the type certification basis

for the Bell Helicopter Textron Model 222U 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

helicopters are exposed to high intensity radiated fields external to

the helicopters.

Issued in Fort Worth, Texas, on December 16, 1994.

Eric Bries,

Acting Manager, Rotorcraft Directorate Aircraft Certification Service.

[FR Doc. 94-31810 Filed 12-23-94; 8:45 am]

BILLING CODE 4910-13-M