[Federal Register Volume 62, Number 187 (Friday, September 26, 1997)]
[Rules and Regulations]
[Pages 50494-50497]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-25509]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-141; Special Conditions No. 25-ANM-132]


Special Conditions: Boeing Model 737-600/-700/-800; High 
Intensity Radiated Fields (HIRF)/Engine Stoppage

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for Boeing Model 737-600/-
700/-800 airplanes. 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

[[Page 50495]]

of safety equivalent to that provided by the existing airworthiness 
standards.

EFFECTIVE DATE: September 17, 1997.

FOR FURTHER INFORMATION CONTACT:
Gregory Dunn, FAA, Standardization Branch, ANM-113, Transport Airplane 
Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., 
Renton, Washington, 98055-4056; telephone (425) 227-2799; facsimile 
(425) 227-1149.

SUPPLEMENTARY INFORMATION: 

Background

    On February 4, 1993, Boeing submitted an application for an 
amendment to Type Certificate A16WE to include the next generation 737 
family of airplanes. Two of these airplanes will have the same length 
as the present 737-300 and 737-500. The third version will be the 
existing 737-400, stretched to add two additional passenger rows. In 
addition, all models will have increased wing size, higher thrust 
engines, and body structure modifications due to increased design 
weights and higher wing and tail loads. The maximum operating altitude 
is to be increased from 37,000 ft. to 41,000 ft. The long range cruise 
speed is increased to 0.78 Mach or better. The range is increased to be 
transcontinental of approximately 2,950 nmi. There is only one engine 
type being offered, which is a derivative of the existing CFM56 
referred to as the CFM56-7.

Type Certification Basis

    Under the provisions of 14 CFR Sec. 21.101, Boeing must show that 
the Model 737-600/-700/-800 airplanes meet the applicable provisions of 
the regulations incorporated by reference in Type Certificate A16WE, or 
the applicable regulations in effect on the date of application for the 
change to the Model 737. The regulations incorporated by reference in 
the type certificate are commonly referred to as the ``original type 
certification basis.'' The certification basis for the Model 737-600/-
700/-800 airplanes includes 14 CFR part 25, as amended by Amendments 
25-1 through 25-77, except as indicated below:

------------------------------------------------------------------------
                                                                At amdt.
          Section No.                       Title                 25-   
------------------------------------------------------------------------
25.365........................  Pressurized Compartment Loads          0
25.561........................  Emergency Landing Conditions--         0
                                 General.                               
25.562........................  Emergency Landing Dynamic           * 64
                                 Conditions.                            
25.571........................  Damage-tolerance and Fatigue     ** 0,77
                                 Evaluation of Structure.               
25.607........................  Fasteners....................    ** 0,77
25.631........................  Bird Strike Damage...........    ** 0,77
25.699........................  Lift and Drag Device             ** 0,77
                                 Indicator.                             
25.783(f).....................  Doors........................   ** 15,77
25.807(c)(3)..................  Emergency Exits..............         15
25.813........................  Emergency Exit Access........         45
25.832........................  Cabin Ozone Concentration....   *** 0,77
25.1309.......................  Equipment, Systems and           ** 0,77
                                 Installations.                         
25.1419(c)....................  Ice Protection...............   ** 23,77
------------------------------------------------------------------------
Boeing has also elected to comply with Amendments 25-78 and 25-80 and   
  portions of Amendments 25-79, 25-84, and 25-86.                       
* Flight attendants seats will be qualified to Technical Standard Order 
  C127. Passenger and flight deck seats will comply with 14 CFR 25.562  
  (a),(b),((c)(1),(2),(3),(4),(7), and (8)).                            
** Applicable to new and significantly modified structure and systems   
  and portions of the airplane affected by these changes. Where two     
  amendment levels are shown for the same paragraph, the number without 
  the asterisks (*) applies to structures, systems, and portions of the 
  airplane which are not new or significantly modified. The structure,  
  systems, and components which comply with the later amendment will be 
  identified in Boeing document D010A001, approved by the FAA and JAA,  
  and referenced on the type certificate data sheet.                    
*** Boeing provides FAA approved data (Document number D6-49779) to 737 
  operators to enable the operators to show ozone compliance per 14 CFR 
  121.578 for their specific route structures.                          

    Amendment level ``0'' is the original published version of Part 25 
(February 1, 1965).
    In addition, the certification basis will be upgraded to include 
the Part 25 complement to any Part 121 amendments adopted prior to the 
certification date and having impact on transport category airplane 
type designs, and these special conditions.
    In addition to the applicable airworthiness regulations and special 
conditions, the Model 737-600/-700/-800 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.
    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 Boeing Model 737-600/-700/-800 
airplanes because of novel or unusual design features, special 
conditions are prescribed under the provisions of 14 CFR 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 14 CFR 11.28 and 
11.29, and become part of the type certification basis in accordance 
with 14 CFR 21.101(b)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should the type certificate for that model be amended 
later to include any other model that incorporates the same novel or 
unusual design feature, or should any other model already included on 
the same type certificate be modified to incorporate the same novel or 
unusual design feature, the special conditions would also apply to the 
other model under the provisions of 14 CFR 21.101(a)(1).

Novel or Unusual Design Features

    The Boeing Model 737-600/-700/-800 airplanes will incorporate new 
avionic/electronic systems, such as the Air Data Inertial Reference 
System (ADIRS) and Common Display System (CDS), that perform critical 
functions. These systems may be vulnerable to HIRF external to the 
airplane. In addition, the CFM56-7B engine proposed for the Boeing 737-
700 airplane is a high-bypass ratio fan jet engine that will not seize 
and produce transient torque loads in the same manner that is 
envisioned by current Sec. 25.361(b)(1) related to ``sudden engine 
stoppage.''

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, a special 
condition is needed for the Boeing Model 737-600/-700/-800, which 
requires that new electrical and electronic 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.
    For the CFM56-7B engine, the limit engine torque load imposed by 
sudden engine stoppage due to malfunction or structural failure (such 
as compressor jamming) has been a specific requirement for transport 
category

[[Page 50496]]

airplanes since 1957. The size, configuration, and failure modes of jet 
engines has change considerably from those envisioned in 14 CFR 
25.361(b) when the engine seizure requirement was first adopted.
    Relative to the engine configurations that existed when the rule 
was developed in 1957, the present generation of engines are 
sufficiently different and novel to justify issuance of a special 
condition to establish appropriate design standards.
    The FAA is developing a new regulation and new advisory circular 
that will provide more comprehensive criteria for treating engine loads 
resulting from structural failures. In the meantime, a special 
condition is needed to establish appropriate criteria for the Boeing 
737-600/-700/-800 airplanes.

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
------------------------------------------------------------------------

Limit Engine Torque Loads for Sudden Engine Stoppage

    In order to maintain the level of safety envisioned by 
Sec. 25.361(b), more comprehensive criteria are needed for the new 
generation of high bypass engines. This special condition distinguishes 
between the more common events and those rare events resulting from 
structural failures in the engine. For these more rare but severe 
events, these criteria allow deformation in the engine supporting 
structure in order to absorb the higher energy associated with the high 
bypass engines, while at the same time protecting the adjacent primary 
structure in the wing and fuselage by applying an additional factor on 
these loads.

Discussion of Comments

    Notice of proposed special conditions No. SC-97-3-NM for the Boeing 
737-600/-700/-800 airplanes was published in the Federal Register on 
May 14, 1997 (62 FR 26453).
    Comments were received from an engine manufacturer who, while 
supporting the need for the engine torque loads requirements, offers 
the following comments for consideration.
    The commenter recommends that the words ``* * * and that could 
cause a shutdown due to vibrations'' be removed from paragraph 
2(b)(1)(i) of the special conditions. The commenter states that its 
position is based on a comparison of the proposed special condition 
with similar work currently underway within the Aviation Rulemaking 
Advisory Committee (ARAC). The commenter notes differences between 
these two proposals. For example, the special condition adds a 
provision that the engine malfunction for limit load calculation be 
such that it ``could cause a shutdown due to engine vibrations,'' while 
this provision was removed from the ARAC proposal, whose intent is to 
address engine events beyond maximum acceleration and other than 
structural failures, seizures, jamming, and unbalance, such as engine 
surge. The commenter further notes that the special condition does not 
explicitly state that the limit torque acts simultaneously with 1g 
flight loads, although this may be intended.
    The FAA recognizes that the ARAC working group is studying this 
issue and that its final proposal may be different from what has 
already been applied as a special condition on several airplanes. 
However, until more definitive criteria have been accepted by industry 
and by the FAA, the special condition will remain unchanged. The 
special condition is based on the assumption that the airplane will be 
subjected to 1g flight loads throughout the engine torque event.

Applicability

    As discussed above, these special conditions are applicable to the 
Model 737-600/-700/-800 airplanes. Should Boeing Commercial Airplane 
Group apply at a later date for a change to the type certificate to 
include another model incorporating the same novel or unusual design 
feature, the special conditions would apply to that model as well under 
the provisions of 14 CFR 21.101(a)(1).
    Under standard practice, the effective date of final special 
conditions would be 30 days after the date of publication in the 
Federal Register; however, as the certification date for the Model 737-
600/-700/-800 airplanes is imminent, the FAA finds that good cause 
exists to make these special conditions effective upon issuance.

Conclusion

    This action affects only certain design features on the Boeing 
Model 737-600/-700/-800 airplanes. 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.

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 Boeing Model 737-600/-700/-800 
airplanes.
    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

[[Page 50497]]

to perform critical functions are not adversely affected when the 
airplane is exposed to high intensity radiated fields.
    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.
    2. Engine Torque Loads. In lieu of compliance with Sec. 25.361(b), 
compliance with the following must be shown:
    (b) For turbine engine installations, the mounts and local 
supporting structure must be designed to withstand each of the 
following:
    (1) The maximum torque load, considered as limit, imposed by:
    (i) sudden deceleration of the engine due to a malfunction that 
could result in a temporary loss of power or thrust capability, and 
that could cause a shutdown due to vibrations; and
    (ii) the maximum acceleration of the engine.
    (2) The maximum torque load, considered as ultimate, imposed by 
sudden engine stoppage due to a structural failure, including fan blade 
failure.
    (3) The load condition defined in paragraph (b)(2) of this section 
is also assumed to act on adjacent airframe structure, such as the wing 
and fuselage. This load condition is multiplied by a factor of 1.25 to 
obtain ultimate loads when the load is applied to the adjacent wing and 
fuselage supporting structure.

    Issued in Renton, Washington, on September 17, 1997.
Vi L. Lipski,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-25509 Filed 9-25-97; 8:45 am]
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