59630 Federal Register / Vol. 70, No. 197 / Thursday, October 13, 2005 / Rules and Regulations 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. NM331; Special Conditions No. 

25–302–SC] 

Special Conditions: Learjet Model 35 

Series; High-Intensity Radiated Fields 

(HIRF) 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Final special conditions; request 

for comments. 

SUMMARY: These special conditions are 

issued for Learjet Model 35 series 

airplanes modified by Avcon Industries 

Inc. 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 new 

Kollsman 24771 Air data computers and 

Thommen AD30 displays. The 

applicable airworthiness regulations do 

not contain adequate or appropriate 

safety standards for the protection of 

these systems from the effects of highintensity 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. 

DATES: The effective date of these 

special conditions is October 4, 2005. 

Comments must be received on or 

before November 14, 2005. 

ADDRESSES: Comments on these special 

conditions may be mailed in duplicate 

to: Federal Aviation Administration, 

Transport Airplane Directorate, 

Attention: Rules Docket (ANM–113), 

Docket No. NM331 1601 Lind Avenue, 

SW., Renton, Washington 98055–4056; 

or delivered in duplicate to the 

Transport Airplane Directorate at the 

above address. All comments must be 

marked Docket No. NM331. 

FOR FURTHER INFORMATION CONTACT: Greg 

Dunn, FAA, Airplane and Flight Crew 

Interface Branch, ANM–111, Transport 

Airplane Directorate, Aircraft 

Certification Service, 1601 Lind 

Avenue, SW., Renton, Washington 

98055–4056; telephone (425) 227–2799; 

facsimile (425) 227–1320. 

SUPPLEMENTARY INFORMATION: 

Comments Invited 

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, we invite 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 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 pre-addressed, stamped 

postcard on which the docket number 

appears. We will stamp the date on the 

postcard and mail it back to you. 

Background 

On August 5, 2005, Avcon Industries, 

Inc., P.O. Box 748, Newton, Kansas, 

67114, applied for a supplemental type 

certificate (STC) to modify Learjet 

Model 35 series airplanes currently 

approved under Type Certificate No. 

A10CE. The Learjet Model 35 airplanes 

are small transport category airplanes 

powered by two turbojet engines, with 

maximum takeoff weight of up to 18,000 

lbs. These airplanes operate with 2- 

person crew and can seat up to 8 

passengers. The proposed modification 

incorporates the installation of 

Kollsman 24771 Air Data Computers 

and Thommen AD30 displays. The 

avionics/electronics and electrical 

systems installed in this airplane are 

flight critical and have the potential to 

be vulnerable to high-intensity radiated 

fields (HIRF) external to the airplane. 

Type Certification Basis 

Under the provisions of 14 CFR 

21.101, Avcon Industries, Inc., must 

show that the Learjet Model 35 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 certification 

basis for the Learjet Model 35 series 

airplanes includes 14 CFR part 25 

effective February 1, 1965, as amended 

by Amendments 25–1, 25–2, 25–4, 25–

7, 25–18, and § 25.571(d) of Amendment 

25–10, Special Conditions set forth in 

FAA letter to Learjet dated March 1, 

1967, and Special Conditions No. 25–

50–CE–6 dated April 18, 1973, and 

Amendment 1 dated September 18, 

1973. The certification basis for Models 

35A also includes Special Conditions 

No. 25–72–CE–8 dated November 3, 

1976, and Amendment 1 dated March 

14, 1978. The certification basis for 

Model 35A (C–21A), in addition to the 

basis listed above, includes Special 

Conditions 25–ANM–28 dated May 3, 

1989. In addition, the certification basis 

includes certain later amended sections 

of the applicable part 25 regulations that 

are not relevant to these special 

conditions. 

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 Model 35 series 

airplanes because of a novel or unusual 

design feature, special conditions are 

prescribed under the provisions of 

§ 21.16. 

In addition to the applicable 

airworthiness regulations and special 

conditions, the Learjet Model 35 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 § 11.38 and become part of the type 

certification basis in accordance with 

§ 21.101. 

Special conditions are initially 

applicable to the model for which they 

are issued. Should Avcon Industries 

Inc., apply at a later date for a 

supplemental type certificate to modify 

any other model included on Type 

Certificate No. A10CE to incorporate the 

Federal Register / Vol. 70, No. 197 / Thursday, October 13, 2005 / Rules and Regulations 59631 

same or similar novel or unusual design 

feature, these special conditions would 

also apply to the other model under the 

provisions of § 21.101. 

Novel or Unusual Design Features 

As noted earlier, the Learjet Model 35 

series airplanes, as modified by Avcon 

Industries, Inc., will incorporate 

Kollsman 24771 Air data computers and 

Thommen AD30 displays. The 

Thommen displays and air data sensor 

perform critical functions. These 

systems may be vulnerable to high 

intensity radiated fields 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 

ground-based 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 series airplanes 

as modified by Avcon Industries, Inc. 

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. 

High-Intensity Radiated Fields (HIRF) 

With the trend toward increased 

power levels from ground-based 

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 

(root-mean-square) 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 table 

below for the frequency ranges 

indicated. Both peak and average field 

strength components from the table are 

to be demonstrated. 

Frequency 

Field strength 

(volts per meter) 

Peak Average 

10 kHz–100 kHz ....... 50 50 

100 kHz–500 kHz ..... 50 50 

500 kHz–2 MHz ........ 50 50 

2 MHz–30 MHz ......... 100 100 

30 MHz–70 MHz ....... 50 50 

70 MHz–100 MHz ..... 50 50 

100 MHz–200 MHz ... 100 100 

200 MHz–400 MHz ... 100 100 

400 MHz–700 MHz ... 700 50 

700 MHz–1 GHz ....... 700 100 

1 GHz–2 GHz ........... 2000 200 

2 GHz–4 GHz ........... 3000 200 

4 GHz–6 GHz ........... 3000 200 

6 GHz–8 GHz ........... 1000 200 

8 GHz–12 GHz ......... 3000 300 

12 GHz–18 GHz ....... 2000 200 

18 GHz–40 GHz ....... 600 200 

The field strengths are expressed in terms 

of peak of the root-mean-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 series airplanes modified by 

Avcon Industries, Inc. Should Avcon 

Industries, Inc., apply at a later date for 

a supplemental type certificate 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 under the provisions of § 21.101. 

Conclusion 

This action affects only certain novel 

or unusual design features on Learjet 

Model 35 series airplanes modified by 

Avcon Industries, Inc. 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 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 supplemental type 

certification basis for Learjet Model 35 

series airplanes modified by Avcon 

Industries, Inc. 

1. Protection from Unwanted Effects 

of High-Intensity 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 October 

4, 2005. 

Ali Bahrami, 

Manager, Transport Airplane Directorate, 

Aircraft Certification Service. 

[FR Doc. 05–20459 Filed 10–12–05; 8:45 am] 

BILLING CODE 4910–13–P