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CFR Citation: 14 CFR Part 25

Docket ID: [Docket No. NM286; Special Conditions No. 25-270-SC]

NOTICE: RULES

ACTION: Airworthiness standards:

DOCUMENT ACTION: Final special conditions; request for comments.

SUBJECT CATEGORY: Special Conditions: Learjet Inc., Model 55, 55B and 55C Airplanes; High Intensity Radiated Fields (HIRF)

DATES: The effective date of these special conditions is July 1, 2004. Comments must be received on or before August 16, 2004.

DOCUMENT SUMMARY: These special conditions are issued for Learjet Inc., Model 55, 55B and 55C airplanes modified by Garrett Aviation Services. These modified airplanes will have a novel or unusual design feature when compared to the state of technology envisioned in the airworthiness standards for transport category airplanes. The modification incorporates the installation of two Honeywell N1 Digital Electronic Engine Controls (DEEC) that perform critical functions. 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 established by the existing airworthiness standards.

SUMMARY: Special conditions—; Learjet Inc., Model 55, 55B and 55C 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 and delivery of the affected airplanes. 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 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 p.m., Monday thru 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 this proposal, 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 1, 2003, Garrett Aviation Services, 1200 North Airport Drive, Capital Airport Springfield, IL 62707, applied for a Supplemental Type Certificate (STC) to modify Learjet Inc., Model 55, 55B and 55C airplanes approved under Type Certificate No. A10CE. The Learjet Inc., Model 55, 55B and 55C airplanes are transport category airplanes. The Learjet Inc., Model 55, 55B and 55C airplanes are powered by two Garrett TFE7313A2B turbofans with a maximum takeoff weight of 21,500 pounds. These aircraft operate with a 2pilot crew and can hold up to 10 passengers. The modification incorporates the installation of Honeywell N1 Digital Electronic Engine Controls (DEEC). The N1 DEEC is a replacement for the existing Analog Electronic Engine Control (EEC), while also providing additional functional capability in the system. The digital avionics/electronics and electrical systems installed under this project in these airplanes have the potential to be vulnerable to HIRF external to the airplane.

Type Certification Basis

Under the provisions of 14 CFR 21.101, Garrett Aviation Services must show that the Learjet Inc., Model 55, 55B and 55C 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 certification basis for the modified Learjet Inc., Model 55, 55B and 55C airplanes include 14 CFR part 25, dated February 1, 1964, as amended by Amendments 251 through 2520 except for special conditions and exceptions noted in Type Certificate Data Sheet (TDCS) A10CE.

If the Administrator finds that the applicable airworthiness regulations (i.e., part 25, as amended) do not contain adequate or appropriate safety standards for the Learjet Inc., Model 55, 55B and 55C airplanes because of novel or unusual design features, special [[Page 42330]]
conditions are prescribed under the provisions Sec. 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Learjet Inc., Model 55, 55B and 55C airplanes must comply with the noise certification requirement of 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 Garrett Aviation Services 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 novel or unusual design feature, these special conditions would also apply to the other model under the provisions of Sec. 21.101.

Novel or Unusual Design Features

The Learjet Inc., Model 55, 55B and 55C airplanes modified by Garrett Aviation Services will incorporate Honeywell N1 DEEC that will perform critical functions. These systems have to potential to be vulnerable to HIRF external to the airplane. The current airworthiness standards (14 CFR part 25) do not contain adequate or appropriate safety standards for the protection of this equipment from the adverse effect 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 that is equivalent to that intended by the regulations incorporated by reference; special conditions are needed for Learjet Inc., Models 55, 55B and 55C airplanes modified by Garrett Aviation Services. These special conditions require that new avionics/electronics and electrical systems 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 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 with the HIRF protection special condition is shown with either 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 identified 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 MHz30MHz....................................... 100 100 30 MHz70 MHz..................................... 50 50 70 MHz100MHz..................................... 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 2 GHz4GHz........................................ 3000 200 4 GHz6 GHz....................................... 3000 200 6 GHz8 GHz....................................... 1000 200 8GHz12 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 Inc., Model 55, 55B and 55C airplanes modified by Garret Aviation Services. Should Garrett Aviation Services 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 novel or unusual design feature, these special conditions would apply to that model as well under the provisions of Sec. 21.101.

Conclusion

This action affects only certain novel or unusual design features on the Learjet Inc., Model 55, 55B and 55C airplanes modified by Garrett Aviation Services. 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 Inc., Model 55, 55B and 55C airplanes modified by Garrett Aviation Services.

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
[[Page 42331]]
to perform critical functions are not adversely affected when the airplane is exposed to highintensity 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 July 1, 2004.
Kalene C. Yanamura,
Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.
[FR Doc. 0416101 Filed 71404; 8:45 am]
BILLING CODE 491013P

FOR FURTHER INFORMATION CONTACT Meghan Gordon, FAA, Standardization Branch, ANM113, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue, SW., Renton, Washington 980554056; telephone (425) 2272138; facsimile (425) 2271149.