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CFR Citation: 14 CFR Part 25

Docket ID: [Docket No. NM282 Special Conditions No. 25-267-SC]

NOTICE: RULES

ACTION: Airworthiness standards:

DOCUMENT ACTION: Final special conditions; request for comments.

SUBJECT CATEGORY: Special Conditions: Learjet Model 35, 35A, 36, and 36A Series Airplanes; High Intensity Radiated Fields (HIRF)

DATES: The effective date of these special conditions is June 3, 2004. Comments must be received on or before August 5, 2004.

DOCUMENT SUMMARY: These special conditions are issued for Learjet Model 35, 35A, 36, and 36A series airplanes modified by Flight Test Associates. These modified airplanes will have novel and unusual design features when compared to the state of technology envisioned in the airworthiness standards for transport category airplanes. The modification incorporates installation of a Honeywell Model BA250 altimeter indicator and a Model AM250 barometric altimeter. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for the protection of these systems from the effects of high intensity radiated fields (HIRF). These special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that provided by the existing airworthiness standards.

SUMMARY: Special conditions—; Learjet Model 35, 35A, 36, 36A series airplanes,

SUPPLEMENTAL INFORMATION

The FAA has determined that notice and opportunity for prior public comment is impracticable because these procedures would significantly delay certification of the airplane and thus delivery of the affected aircraft. In addition, the substance of these special conditions has been subject to the public comment process in several prior instances with no substantive comments received. The FAA therefore finds that good cause exists for making these special conditions effective upon issuance; however, the FAA invites interested persons to participate in this rulemaking by submitting written comments, data, or views. The most helpful comments reference a specific portion of the special conditions, explain the reason for any recommended change, and include supporting data. We ask that you send us two copies of written comments.

We will file in the docket all comments we receive, as well as a report summarizing each substantive public contact with FAA personnel concerning these special conditions. The docket is available for public inspection before and after the comment closing date. If you wish to review the docket in person, go to the address in the ADDRESSES section of this preamble between 7:30 a.m. and 4:00 p.m., Monday through Friday, except Federal holidays.

We will consider all comments we receive on or before the closing date for comments. We will consider comments filed late if it is possible to do so without incurring expense or delay. We may change these special conditions based on the comments we receive.

If you want the FAA to acknowledge receipt of your comments on these special conditions, include with your comments a preaddressed, stamped postcard on which the docket number appears. We will stamp the date on the postcard and mail it back to you.

Background

On December 19, 2003, Flight Test Associates, Incorporated, of Mojave, California, applied to the FAA, Los Angeles Aircraft Certification Office, for a supplemental type certificate (STC) to modify Learjet Model 35, 35A, 36, and 36A series airplanes. These models are currently approved under Type Certificate No. A10CE. The proposed modification incorporates installation of the digital Honeywell Model BA250 altimeter indicator and Model AM250 barometric altimeter as primary altimeters. The information presented by this equipment is flight critical. The digital altimeters installed in these airplanes have the potential to be vulnerable to highintensity radiated fields (HIRF) external to the airplane.

Type Certification Basis

Under the provisions of 14 CFR 21.101, Flight Test Associates must show that the Learjet Model 35, 35A, 36, and 36A series airplanes, as changed, continue to meet the applicable provisions of the regulations incorporated by reference in Type Certificate No. A10CE, or the applicable regulations in effect on the date of application for the change. The regulations incorporated by reference in the type certificate are commonly referred to as the ``original type certification basis.''

The regulations incorporated by reference in Type Certificate No. A10CE include 14 CFR part 25 as amended by Amendments 252, 254, 257, 2510, and 2518.

If the Administrator finds that the applicable airworthiness regulations (i.e., 14 CFR part 25, as amended) do not contain adequate or appropriate safety standards for the modified Learjet Model 35, 35A, 36, and 36A series airplanes because of a novel or unusual design feature, special conditions are prescribed under the provisions of Sec. 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Learjet Model 35, 35A, 36, and 36A series airplanes must comply with the fuel vent and exhaust emission requirements of 14 CFR part 34 and the noise certification requirements of 14 CFR part 36.

Special conditions, as defined in 14 CFR 11.19, are issued in accordance with Sec. 11.38 and become part of the type certification basis in accordance with Sec. 21.101.

Special conditions are initially applicable to the model for which they are issued. Should Flight Test Associates apply at a later date for a supplemental type certificate to modify any other model included on the same type certificate to incorporate the same or similar novel or unusual design feature, these special conditions would also apply to the other model under the provisions of Sec. 21.101.
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Novel or Unusual Design Features

As noted earlier, the Learjet Model 35, 35A, 36, and 36A series airplanes modified by Flight Test Associates will incorporate new dual primary altimeters that will perform critical functions. These systems may be vulnerable to HIRF external to the airplane. The current airworthiness standards of part 25 do not contain adequate or appropriate safety standards for the protection of this equipment from the adverse effects of HIRF. Accordingly, this system is considered to be a novel or unusual design feature.

Discussion

There is no specific regulation that addresses protection requirements for electrical and electronic systems from HIRF. Increased power levels from groundbased radio transmitters and the growing use of sensitive avionics/electronics and electrical systems to command and control airplanes have made it necessary to provide adequate protection.

To ensure that a level of safety is achieved equivalent to that intended by the regulations incorporated by reference, special conditions are needed for the Learjet Model 35, 35A, 36, and 36A series airplanes modified by Flight Test Associates. These special conditions require that new primary altimeters that perform critical functions be designed and installed to preclude component damage and interruption of function due to both the direct and indirect effects of HIRF. HighIntensity Radiated Fields (HIRF)

With the trend toward increased power levels from groundbased transmitters, and the advent of space and satellite communications, coupled with electronic command and control of the airplane, the immunity of critical digital avionics/electronics and electrical systems to HIRF must be established.

It is not possible to precisely define the HIRF to which the airplane will be exposed in service. There is also uncertainty concerning the effectiveness of airframe shielding for HIRF. Furthermore, coupling of electromagnetic energy to cockpitinstalled equipment through the cockpit window apertures is undefined. Based on surveys and analysis of existing HIRF emitters, an adequate level of protection exists when compliance is shown with either HIRF protection special condition paragraph 1 or 2 below:

1. A minimum threat of 100 volts rms (rootmeansquare) per meter electric field strength from 10 KHz to 18 GHz.

a. The threat must be applied to the system elements and their associated wiring harnesses without the benefit of airframe shielding.

b. Demonstration of this level of protection is established through system tests and analysis.

2. A threat external to the airframe of the field strengths identifed in the following table for the frequency ranges indicated. Both peak and average field strength components from the table are to be demonstrated.
Field strength (volts per meter) Frequency
Peak Average 10 kHz100 kHz.................................. 50 50 100 kHz500 kHz................................. 50 50 500 kHz2 MHz................................... 50 50 2 MHz30 MHz.................................... 100 100 30 MHz70 MHz................................... 50 50 70 MHz100 MHz.................................. 50 50 100 MHz200 MHz................................. 100 100 200 MHz400 MHz................................. 100 100 400 MHz700 MHz................................. 700 50 700 MHz1 GHz................................... 700 100 1 GHz2 GHz..................................... 2000 200 2GHz4 GHz...................................... 3000 200 4 GHz6 GHz..................................... 3000 200 6 GHz8 GHz..................................... 1000 200 8 GHz12 GHz.................................... 3000 300 12 GHz18 GHz................................... 2000 200 18 GHz40 GHz................................... 600 200 The field strengths are expressed in terms of peak of the rootmean square (rms) over the complete modulation period.

The threat levels identified above are the result of an FAA review of existing studies on the subject of HIRF, in light of the ongoing work of the Electromagnetic Effects Harmonization Working Group of the Aviation Rulemaking Advisory Committee.

Applicability

As discussed above, these special conditions are applicable to Learjet Model 35, 35A, 36, and 36A series airplanes modified by Flight Test Associates. Should Flight Test Associates apply at a later date for an STC to modify any other model included on Type Certificate No. A10CE to incorporate the same or similar novel or unusual design feature, these special conditions would apply to that model as well as under the provisions of 14 CFR 21.101.

Conclusion

This action affects only certain novel or unusual design features on the Learjet Model 35, 35A, 36, and 36A series airplanes modified by Flight Test Associates. 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 airplane.

The substance of these special conditions has been subjected to the notice and comment procedure in several prior instances and has been derived without substantive change from those previously issued. Because a delay would significantly affect the certification of the airplane, which is imminent, the FAA has determined that prior public notice and comment are unnecessary and impracticable, and good cause exists for adopting these special conditions 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 described above.

List of Subjects in 14 CFR Part 25

Aircraft, Aviation safety, Reporting and record keeping requirements.
The authority citation for these special conditions is as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704. The Special Conditions
Accordingly, pursuant to the authority delegated to me by the Administrator, the following special conditions are issued as part of the supplemental type certification basis for the Learjet Model 35, 35A, 36, and 36A series airplanes modified by Flight Test Associates:

1. Protection from Unwanted Effects of HighIntensity Radiated Fields (HIRF). Each electrical and electronic system that performs critical functions must be designed and installed to ensure that the operation and operational capability of these systems to perform critical functions are not adversely affected when the airplane is exposed to high intensity radiated fields.

2. For the purpose of these special conditions, the following definition applies:

Critical Functions: Functions whose failure would contribute to or cause a failure condition that would prevent the continued safe flight and landing of the airplane.

Issued in Renton, Washington, on June 3, 2004.
Franklin Tiangsing,
Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.
[FR Doc. 0415037 Filed 7204; 8:45 am]
BILLING CODE 491013P

FOR FURTHER INFORMATION CONTACT Mr. Steve Edgar, FAA, Standardization Branch, ANM113, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., Renton, Washington 980554056; telephone (425) 2272025; facsimile (425) 2271149.