The modification that is the subject of these special conditions incorporates the installation of Innovative Solutions & Support air data display units (ADDU). The ADDU is a replacement for the existing analog flight instrumentation, and provides additional functional capability and redundancy in the system. The avionics/electronics and electrical systems installed in the subject Cessna airplanes have the potential to be vulnerable to HIRF external to the airplane. Type Certification Basis

Under the provisions of 14 CFR 21.101, ElectroSonics must show that the Cessna Model 500, 550, S550, and 560 airplanes, as changed, continue to meet the applicable provisions of the regulations incorporated by reference in Type Certificate No. A22CE, 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 included in the certification basis for theses airplanes are as follows:
1. For the Cessna Model 500 Airplane

In addition to the applicable airworthiness regulations and special conditions, these Cessna Model 500, 550, S550, and 560 airplanes must comply with the fuel vent and exhaust emission requirements of part 34 and the noise certification requirements of part 36.
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The Effect of Special Conditions on the Type Certification Basis

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 Cessna Model 500, 550, S550, and 560 airplanes modified by ElectroSonics because of a novel or unusual design feature, special conditions are prescribed under the provisions of Sec. 21.16.

Special conditions, as defined in Sec. 11.19, are issued in accordance with Sec. 11.38. In accordance with Sec. 21.101(b)(2), the special conditions approved in this document will form an additional part of the type certification basis for these airplanes.

Special conditions are initially applicable to the model for which they are issued. Should ElectroSonics 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(a)(1).

Novel or Unusual Design Features

As noted earlier, the Cessna Model 500, 550, S550, and 560 airplanes modified by ElectroSonics will incorporate a dual electronic primary flight display system that will perform critical functions. This system 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 that is equivalent to that intended by the regulations incorporated by reference, special conditions are needed for the Cessna Model 500, 550, S550, and 560 airplanes modified by ElectroSonics. 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 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, 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 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 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 Cessna Model 500, 550, S550, and 560 airplanes modified by ElectroSonics. Should ElectroSonics apply at a later date for a supplemental type certificate to modify any other model included on Type Certificate A22CE 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(a)(1).

Conclusion

This action affects only certain novel or unusual design features on the Cessna Model 500, 550, S550, and 560 airplanes modified by ElectroSonics. 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 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.

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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 Cessna Aircraft Company Model 500, 550, S550, and 560 series airplanes modified by ElectroSonics:

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 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 April 10, 2001. Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.
[FR Doc. 019531 Filed 41701; 8:45 am] BILLING CODE 491013U

FOR FURTHER INFORMATION CONTACT For information concerning the certification program for Cessna Model 500, 550, S550, and 560 airplanes, contact: Meghan Gordon, Federal Aviation Administration, Standardization Branch, ANM113, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., Renton, Washington 980554056; telephone (425) 2272138; fax (425) 2271149.

For information on the general subject of HIRF, contact: Stephen Slotte, Federal Aviation Administration, Transport airplane Directorate, Airplane and Flight Crew Interface Branch, ANM111, 1601 Lind Avenue SW., Renton, Washington 980554056; telephone (425) 227 2315; fax (425) 2271320.