In accordance with 14 CFR part 36.1(a)(4), compliance with the noise requirements was not shown for the aircraft. Therefore, the engine installations under this supplemental type certificate are only eligible for external load operations excepted by Sec. 36.1(a)(4) and defined under Sec. 133.1(b). Any alteration to the aircraft for special purpose not identified above will require further FAA approval and in addition, may require noise testing, flight testing, or a combination of noise and flight testing.

In addition, the certification basis includes an equivalent safety finding pertaining to a limitation associated with repetitive high torque cycle events that is not relevant to this special condition.

If the Administrator finds that the applicable airworthiness regulations do not contain adequate or appropriate safety standards for this STC because of a novel or unusual design feature, special conditions are prescribed under the provisions of Sec. 21.16.

The FAA issues special conditions as defined in Sec. 11.19, and issued in accordance with Sec. 11.38, and they become part of the STC certification basis under Sec. 21.17(a)(2).

Special conditions are initially applicable to the model, the modification, or a combination of the model and the modification for which they are issued. Should this STC be revised to include any other model that incorporates the same novel or unusual design feature, this special condition would also apply to the other model under the provisions of Sec. 21.101.

Novel or Unusual Design Features

The GHTI UH1H Restricted Category Helicopter with a Pratt & Whitney PT667D engine installed will incorporate the following novel or unusual design features: Electrical, electronic, or a combination of electrical and electronic (electrical/electronic) systems, specifically a FADEC, that will be performing critical control functions for the continued safe flight and landing of the helicopter. A FADEC is an electronic device that performs the critical functions of engine control during flight operations.

Discussion

The DynCorp International installation of the PT667D in the UH1H helicopter, at the time of application, was identified as incorporating an electronic FADEC system. After the design is finalized, DynCorp International will provide the FAA with a preliminary hazard analysis. This analysis will identify the critical control functions that are required for safe flight and landing that are performed by the FADEC system.

Recent advances in technology have given rise to the application in aircraft designs of advanced electrical/electronic systems that perform critical control functions. These advanced systems respond to the transient effects of induced electrical current and voltage caused by HIRF incidents 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 Sec. 29.1309(a). Higher energy levels radiate from operational transmitters currently used for radar, radio, and television. Also, the number of transmitters has increased significantly.

Existing aircraft or alteration 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 the technological advances in helicopter design and the changing environment have resulted in an increased level of
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vulnerability of the electrical/electronic systems required for the continued safe flight and landing of the helicopter. The design and installation of these systems will provide effective measures to protect this engine installation on this helicopter against the adverse effects of exposure to HIRF. The following primary factors contributed to the current conditions: (1) Increased use of sensitive electronics that perform critical control 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.

On July 30, 2007, we issued a final HIRF rule (72 FR 44016, August 6, 2007). This rule provides standards to protect aircraft electrical and electronic systems from HIRFs. It was effective September 5, 2007. However, that rule included provisions that provide relief from the new testing requirements for equipment previously certificated under HIRF special conditions issued in accordance with 14 CFR Sec. 21.16. To obtain this relief, the applicant must be able to
(1) Provide evidence that the system was the subject of HIRF special conditions issued before December 1, 2007;
(2) Show that there have been no system design changes that would invalidate the HIRF immunity characteristics originally demonstrated under the previously issued HIRF special conditions; and
(3) Provide the data used to demonstrate compliance with the HIRF special conditions under which the system was previously approved.

DynCorp's FADEC installation is eligible for this relief provided in 14 CFR Sec. 29.1317(d) of the final HIRF rule. However, to meet their HIRF requirements, they must comply with this Special Condition, which is based on similar, historical HIRF protections requirements.

These special conditions will require the systems that perform critical control 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 control functions are not adversely affected when the aircraft is exposed to the defined HIRF test environment. The FAA has determined that the test environment defined in Table 1 is acceptable for critical control functions in helicopters.

The applicant may also demonstrate by a laboratory test that the electrical/electronic systems that perform critical control 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 200 volts per meter (v/m) is more appropriate for critical functions during VFR operations. Laboratory test levels are defined according to RTCA/DO 160D Section 20 Category Y (200 v/m and 300 mA). As defined in DO160D Section 20, the test levels are defined as the peak of the root means squared (rms) envelope. As a minimum, the modulations required for RTCA/DO160D Section 20 Category Y will be used. Other modulations should be selected as 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 worstcase 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.

Applicants must perform a preliminary hazard analysis to identify electrical/electronic systems that perform critical control functions. The term ``critical control'' means those functions whose failure would contribute to or cause an unsafe condition that would prevent the continued safe flight and landing of the helicopter. The FADEC system identified by the hazard analysis as performing critical control functions is required to have HIRF protection.

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 FADEC system to the defined environment or laboratory testing may not be combined. The laboratory test allows some frequency areas to be undertested 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. If the worstcase 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 control 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 casebycase basis.
Table 1.Field Strength Volts/Meter
Frequency Peak Average 10100 KHz........................................ 150 150 100500 KHz....................................... 200 200 5002000 KHz...................................... 200 200 230 MHz.......................................... 200 200 30100 MHz........................................ 200 200 100200 MHz....................................... 200 200 200400 MHz....................................... 200 200 400700 MHz....................................... 730 200 7001000 MHz...................................... 1400 240 [[Page 64532]]
12 GHz........................................... 5000 250 24 GHz........................................... 6000 490 46 GHz........................................... 7200 400 68 GHz........................................... 1100 170 812 GHz.......................................... 5000 330 1218 GHz......................................... 2000 330 1840 GHz......................................... 1000 420 Applicability

As discussed previously, this special condition is applicable to Supplemental Type Certificate (STC) Project Number ST2902RCR, for the installation of a Pratt & Whitney PT667D turbine engine in GHTI UH1H military surplus helicopters type certificated under TC R00002RC. Should DynCorp International apply at a later date for a change to the STC to include another model incorporating the same novel or unusual design feature, the special condition would apply to that STC modification as well under the provisions of Sec. 21.101.

Conclusion

This action affects only certain novel or unusual design features associated with this STC project. 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 helicopter.

The substance of this special condition has been subjected to a notice and comment period in several prior instances and has been derived without substantive change from those previously issued. It is unlikely that prior public comment would result in a significant change from the substance contained herein. For this reason, the FAA has determined that prior public notice and comment are unnecessary, and good cause exists for adopting this special condition upon issuance. The FAA is requesting comments to allow interested persons to submit views that may not have been submitted in response to the prior opportunities for comment.

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: 42 U.S.C. 7572; 49 U.S.C. 106(g), 40105, 40113, 4470144702, 44704, 44709, 44711, 44713, 44715, 45303.

The 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 basis for STC Project ST2902RCR, installation of PT667D on Global Helicopter Technology, Inc. (GHTI), Model UH1H, Restricted Category Helicopters, type certificated under TC R00002RC.

Protection for Electrical and Electronic Systems From High Intensity Radiated Fields.

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

2. For the purpose of this special condition, critical control functions are defined as those functions, whose failure would contribute to, or cause, an unsafe condition that would prevent the continued safe flight and landing of the aircraft.

Issued in Fort Worth, Texas, on November 7, 2007. Mark R. Schilling,
Acting Manager, Aircraft Certification Service, Rotorcraft Directorate. [FR Doc. 075698 Filed 111507; 8:45 am]
BILLING CODE 491013P

FOR FURTHER INFORMATION CONTACT Tyrone D. Millard, FAA, Rotorcraft Directorate, Rotorcraft Standards Staff, Fort Worth, Texas 761930110; telephone 8172225439, fax 8172225961.