[Federal Register Volume 62, Number 218 (Wednesday, November 12, 1997)]
[Rules and Regulations]
[Pages 60640-60642]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-29730]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-144; Special Conditions No. 25-ANM-134]


Special Conditions: Learjet Inc. Model 55 Airplane; 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 55 
airplanes modified by Learjet. These airplanes will have novel and 
unusual design features when compared to the state of technology 
envisioned in the airworthiness standards for transport category 
airplanes. 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.

DATES: The effective date of these special conditions is October 31, 
1997. Comments must be received on or before December 29, 1997.

ADDRESSES: Comments on these special conditions may be mailed in 
duplicate to: Federal Aviation Administration, Office of the Assistant 
Chief Counsel, Attn: Rules Docket (ANM-7), Docket No. NM-144, 1601 Lind 
Avenue SW., Renton, Washington, 98055-4056; or delivered in duplicate 
to the Office of the Assistant Chief Counsel at the above address. 
Comments must be marked: Docket No. NM-144. Comments may be inspected 
in the Rules Docket weekdays, except Federal holidays, between 7:30 
a.m. and 4:00 p.m.

FOR FURTHER INFORMATION CONTACT: Connie Beane, FAA, Standardization 
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue SW., Renton, Washington, 98055-4056; 
telephone (425) 227-2796; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA has determined that good cause exists for making these 
special conditions effective upon issuance; however, interested persons 
are invited to submit such written data, views, or arguments as they 
may desire. Communications should identify the regulatory docket and 
special condition number and be submitted in duplicate to the address 
specified above. All communications received on or before the closing 
date for comments will be considered by the Administrator. These 
special conditions may be changed in light of the comments received. 
All comments submitted will be available in the Rules Docket for 
examination by interested persons, both before and after the closing 
date for comments. A report summarizing each substantive public contact 
with FAA personnel concerning this rulemaking will be filed in the 
docket. Persons wishing the FAA to acknowledge receipt of their 
comments submitted in response to this request must submit with those 
comments a self-addressed, stamped postcard on which the following 
statement is made: ``Comments to Docket No. NM-144.'' The postcard will 
be date stamped and returned to the commenter.

Background

    On August 27, 1997, Learjet Inc. applied for a supplemental type

[[Page 60641]]

certificate (STC) to modify Learjet Model 55 airplanes listed on Type 
Certificate A10CE. The modification incorporates the installation of a 
digital electronic flight instrument system (EFIS) for display of 
critical flight parameters (attitude) to the crew. These displays can 
be susceptible to disruption to both command/response signals as a 
result of electrical and magnetic interference. This disruption of 
signals could result in loss of all critical flight displays and 
annunciations or present misleading information to the pilot.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Learjet Inc. must show that 
the Learjet Model 55 airplane, as changed, continues to meet the 
applicable provisions of the regulations incorporated by reference in 
Type Certificate 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 Model 55 airplane includes 14 CFR part 25, as amended by 
Amendments 25-2 through 25-4, 25-7, 25-10, 25-12, 25-18, 25-21, 25-30, 
and certain later amendments, special conditions, exemptions, and 
optional requirements listed in the type certificate data sheet that 
are not relevant to these special conditions. In addition, the 
certification basis for the modifications, and for areas affected by 
the modifications, will be amended to include the following sections:

------------------------------------------------------------------------
               Section                Amendment           Title         
------------------------------------------------------------------------
25.901..............................     25-38   Installation.          
25.1301(d)..........................     25-38   Function and           
                                                  Installation.         
25.1303.............................     25-38   Flight and navigation  
                                                  instruments.          
25.1309.............................     25-41   Equipment, systems, and
                                                  installations.        
25.1321.............................     25-41   Arrangement and        
                                                  visibility.           
25.1322.............................     25-38   Warning, caution, and  
                                                  advisory lights.      
25.1331.............................     25-41   Instruments using a    
                                                  power supply.         
25.1333.............................     25-41   Instrument systems.    
25.1335.............................     25-41   Flight director        
                                                  systems.              
------------------------------------------------------------------------

    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 55 airplane because 
of novel or unusual design features, special conditions are prescribed 
under the provisions of Sec. 21.16 to establish a level of safety 
equivalent to that established in the regulations.
    Special conditions, as appropriate, are issued in accordance with 
14 CFR 11.49 after public notice, as required by Secs. 11.28 and 11.29, 
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 Learjet Inc. apply at a later date for design 
change approval to modify any other model already included on the same 
type certificate to incorporate the same novel or unusual design 
feature, the special conditions would also apply to the other model 
under the provisions of Sec. 21.101(a)(1).

Novel or Unusual Design Features

    The modified Learjet Model 55 will incorporate a new electronic 
flight instrument system that performs critical functions. This system 
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 ground-based radio transmitters and the growing use 
of sensitive electrical and electronic 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 55, which require that new 
electrical and electronic systems, such as the EFIS, 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, plus the advent of space and satellite communications, 
coupled with electronic command and control of the airplane, the 
immunity of critical digital avionics 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 cockpit-installed 
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 paragraphs 1, or 2 below:
    1. A minimum threat of 100 volts per meter peak 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 following field 
strengths for the frequency ranges indicated.

------------------------------------------------------------------------
                                                        Peak (V/ Average
                       Frequency                           M)      (V/M)
------------------------------------------------------------------------
10 KHz-100 KHz........................................       50       50
100 KHz-500 KHz.......................................       60       60
500 KHz-2 MHz.........................................       70       70
2 MHz-30 MHz..........................................      200      200
30 MHz-100 MHz........................................       30       30
100 MHz-200 MHz.......................................      150       33
200 MHz-400 MHz.......................................       70       70
400 MHz-700 MHz.......................................    4,020      935
700 MHz-1 GHz.........................................    1,700      170
1 GHz-2 GHz...........................................    5,000      990
2 GHz-4 GHz...........................................    6,680      840
4 GHz-6 GHz...........................................    6,850      310
6 GHz-8 GHz...........................................    3,600      670
8 GHz-12 GHz..........................................    3,500    1,270
12 GHz-18 GHz.........................................    3,500      360
18 GHz-40 GHz.........................................    2,100      750
------------------------------------------------------------------------

Applicability

    As discussed above, these special conditions are applicable to 
Learjet Model 55 airplanes modified by Learjet. Should Learjet apply at 
a later date for design change approval to modify any other model 
included on the same type certificate 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 design features on Learjet Model 
55 airplanes modified by Learjet. 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 the special conditions for this airplane has been 
subjected to the notice and comment procedure 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.

[[Page 60642]]

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 immediately. Therefore, these special conditions are being 
made effective 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 Learjet Model 55 airplanes modified by 
Learjet 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.
    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 31, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 97-29730 Filed 11-10-97; 8:45 am]
BILLING CODE 4910-13-P