The FDS2000 system is a replacement of the existing electro mechanical Attitude Directional Indicator (ADI) and Horizontal Situational Indicator (HSI) flight instruments. It also provides additional functional capability and redundancy in the system.

The AHS3000A system is a replacement for the existing electro mechanical vertical and directional gyros. It also provides additional functional capability and redundancy in the system.

The avionics/electronics and electrical systems installed in the Gulfstream Model G1159, G1159A, and G1159B airplanes have the potential to be vulnerable to highintensity radiated fields (HIRF) external to the airplane.

The subject Gulfstream airplanes are Ttail, low sweptwing small transport category airplanes. The Model G1159 airplane is powered by two Rolls Royce SPEY RB (163) 5118 series engines mounted on pylons extending from the aft fuselage, and it has a maximum takeoff weight of 64,800 pounds. The Models G1159A and G1159B are slightly larger than the Model G1159. These models are powered by two Rolls Royce SPEY RB (16325) 5118 series engines, and have a maximum takeoff
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weight of 69,700 pounds. This series of airplanes operates with a 2 pilot crew and can hold up to 19 passengers.

Type Certification Basis

Under the provisions of 14 CFR Sec. 21.101, Duncan Aviation must show that the Gulfstream Models G1159, G1159A, and G1159B airplanes, as modified, continue to meet the applicable provisions of the regulations incorporated by reference in Type Certificate No. A12EA, or the applicable regulations in effect on the date of application for the modification. 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. A12EA are as follows:
1. For the Gulfstream Model G1159 Airplane

The special conditions approved in this document will form an additional part of the type certification basis for these airplanes.

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 Gulfstream Model G1159, 11 59A, and G1159B airplanes modified by Duncan Aviation because of a novel or unusual design feature, special conditions are prescribed under the provisions of Sec. 21.16.

Special conditions, as appropriate, are issued in accordance with Sec. 11.49, 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).

Special conditions are initially applicable to the model for which they are issued. Should Duncan Aviation apply at a later date for a supplemental type certificate to modify any other model already 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(a)(1).

Novel or Unusual Design Features

The Gulfstream Model G1159, G1159A, and G1159B airplanes modified by Duncan Aviation will incorporate new avionics/electronics and electrical systems that will perform critical functions. These systems include a new flight display system and a new attitude heading reference system. These systems may be vulnerable to HIRF external to the airplane.

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 Gulfstream Model G1159, G1159A, and G 1159B airplanes modified by Duncan Aviation. 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, plus the advent of space and satellite communications coupled with electronic command and control of
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the airplane, and the use of composite material in the airplane structure, 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, alternatively, paragraph 2., below:

1. A minimum threat of 100 volts rms 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.

Or

2. A threat external to the airframe for both of the following field strengths for the frequency ranges indicated. Both peak and average field strength components from Table 1 are to be demonstrated. Table 1
Field Strength (volts per Frequency meter)
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 2 GHz4 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 in Table 1 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 the Gulfstream Model G1159, G1159A, and G1159B series airplanes modified by Duncan Aviation. Should Duncan Aviation apply at a later date for a supplemental type certificate to modify any other model included on Type Certificate No. A12EA to incorporate the same novel or unusual design feature, the special conditions would apply to that model as well under the provisions of Sec. 21.101(a)(1).

Conclusion

This action affects only certain novel or unusual design features on Gulfstream Model G1159, G1159A, and G1159B airplanes modified by Duncan Aviation. 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.

As stated previously, the substance of these special conditions has been subjected to the 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, and 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 recordkeeping 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 type certification basis for Gulfstream Aerospace Model G1159, G 1159A, and G1159B airplanes modified by Duncan Aviation:

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 this special condition, 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 November 29, 2000. Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.
[FR Doc. 0031085 Filed 12500; 8:45 am] BILLING CODE 491013U

FOR FURTHER INFORMATION CONTACT For information concerning the certification program for Gulfstream Model G1159, G1159A, and G1159B series airplanes, contact: Meghan Gordon, Federal Aviation Administration, Transport Airplane Directorate, Standardization Branch, ANM113, 1601 Lind Avenue SW., Renton, Washington 980554056; telephone (425) 2272138; fax (425) 2271149.

For information on the general subject of HIRF, contact: Massoud Sadeghi, Federal Aviation Administration, Transport airplane Directorate, Airplane and Flight Crew Interface Branch, ANM111, 1601 Lind Avenue SW., Renton, Washington 980554056; telephone (425) 227 2117; fax (425) 2271320.