[Federal Register Volume 62, Number 200 (Thursday, October 16, 1997)]
[Rules and Regulations]
[Pages 53737-53739]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-27503]


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

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-135; Special Conditions No. 25-ANM-133]


Special Conditions: Boeing, Model 767-27C Airplanes, Airborne 
Warning and Control System (AWACS) Modification; Liquid Oxygen System

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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

SUMMARY: These special conditions are issued for Boeing Model 767-27C 
airplanes modified by installation of an Airborne Warning and Control 
System (AWACS). These airplanes will be equipped with an oxygen system 
utilizing liquid oxygen (LOX). The applicable regulations do not 
contain adequate or appropriate safety standards for the design and 
installation of oxygen systems utilizing LOX for storage. These 
standards are intended to ensure that the design and installation of 
the liquid oxygen system is such that a level of safety equivalent to 
that established by the airworthiness standards for transport category 
airplanes is provided.

EFFECTIVE DATE: November 17, 1997.

FOR FURTHER INFORMATION CONTACT: William Schroeder, FAA, 
Standardization Branch, ANM-113, Transport Airplane Directorate, 
Airplane Certification Service, 1601 Lind Avenue SW, Renton, Washington 
98055-4056; telephone (425) 227-2148.

SUPPLEMENTARY INFORMATION:

Background

    On May 25, 1993, Boeing Commercial Airplane Group--Wichita 
Division, applied for a supplemental type certificate (STC) to modify 
Boeing Model 767-27C airplanes to an Airborne Warning and Control 
System (AWACS) configuration. The AWACS modification includes 
installation of equipment consoles, seats for console operators, a 
liquid oxygen (LOX) system (liquid oxygen converter, valves, 
evaporating coils, lines, regulators, indicators, fittings, etc.), and 
a radome on the top of the airplane. Boeing will modify the aft lower 
lobe with hydraulics for the AWACS antenna drive unit, high-powered 
radio frequency units for the AWACS radar, and other AWACS hardware. 
Boeing has designed the LOX installation to provide a supply of 
breathing oxygen sufficient to allow operation of the airplane in the 
unpressurized mode if this becomes necessary. The FAA will approve the 
performance of the oxygen system during certification testing.
    There are no specific regulations that address the design and 
installation of oxygen systems that utilize liquid oxygen. Existing 
requirements, such as Secs. 25.1309, 25.1441 (b) & (c), 25.1451, and 
25.1453 in the Boeing Model 767-27C original type certification basis, 
applicable to this modification, provide some design standards for crew 
and medical oxygen system installations. However, the FAA must specify 
additional design standards for systems utilizing liquid oxygen to 
ensure that an acceptable level of safety is maintained.

Supplemental Type Certification Basis

    Under the provisions of Secs. 21.101 (a) and (b), Boeing Commercial 
Airplane Group must show that the modified Model 767-27C continues to 
meet the applicable provisions of the regulations incorporated by 
reference in Type Certificate (TC) No. A1NM, 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 incorporated by reference in TC A1NM are basically as 
follows: Part 25 of the FAR, as amended by Amendments 25-1 through 25-
37, plus certain later amended sections as specified in Type 
Certificate Data Sheet A1NM. In addition, the certification basis 
includes certain special conditions, exemptions and optional 
requirements that are not relevant to these special conditions. Also, 
the modified Model 767-27C must continue to comply with the fuel 
venting and exhaust emission requirements of part 34 (previously 
Special Federal Aviation Regulation 27), and the noise certification 
requirements of part 36 in effect on the date the STC is issued.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended and applicable) do not contain 
adequate or appropriate safety standards for the modified Model 767-27C 
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 of the FAR after public notice, as required by Sec. 11.28 
and Sec. 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 the applicant apply 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, 
the special conditions would apply to the other model under the 
provisions of Sec. 21.101(a)(1).

Discussion

    There are no specific regulations that address the design and 
installation of oxygen systems that utilize liquid oxygen for storage. 
Existing requirements, such as Secs. 25.1309, 25.1441 (b) and (c), 
25.1451, and 25.1453 of the Boeing 767-200 series certification basis 
applicable to this STC project, provide some design standards 
appropriate for oxygen system installations. However, additional design 
standards for oxygen systems utilizing liquid oxygen are needed to 
supplement the existing applicable requirements. The quantity of liquid 
oxygen involved in this installation and the potential for unsafe 
conditions that may result when the oxygen content of an enclosed area 
becomes too high because of system leaks, malfunction, or damage from 
external sources, make it necessary to assure adequate safety standards 
are applied to the design and installation of the system in Boeing 
Model 767-27C airplanes.
    To ensure that a level of safety is achieved for modified Boeing 
Model 767-27C airplanes, utilizing liquid oxygen as a storage medium 
for an oxygen system, equivalent to that intended by the regulations 
incorporated by reference, special

[[Page 53738]]

conditions are needed which require those oxygen systems to be designed 
and installed to preclude or minimize the existence of unsafe 
conditions that can result from system leaks, malfunction, 
installation, or damage from external sources.
    Application by Boeing for approval of oxygen systems utilizing 
liquid oxygen as a storage medium installed in transport airplanes, and 
the unsafe conditions that can exist when the oxygen content of an 
enclosed area becomes too high because of system leaks, malfunction, 
installation or damage from external sources, make development and 
application of appropriate additional design and installation standards 
necessary.

Discussion of Comments

    On November 21, 1996, the FAA published Notice of Proposed Special 
Conditions No. SC-96-8-NM for the Boeing Model 767-27C liquid oxygen 
system installation in the Federal Register (61 FR 59202). The 
Department of the Air Force, commenting to the docket by letter, 
recommended additional requirements for design and installation of the 
LOX system. Based on some of those recommendations, the FAA revised 
special conditions f. and m. and republished the special conditions as 
Supplemental Notice SC-96-8A-NM on July 21, 1997 (62 FR 38945).
    Boeing Commercial Airplane Group, the applicant, provided the only 
comments in response to Supplemental Notice SC-96-8A.
    Boeing suggests that paragraph ``f'' of the special conditions be 
revised to read:
    ``The system shall include provisions to ensure complete conversion 
of the liquid oxygen to gaseous oxygen. The resultant oxygen gas must 
be delivered to the first oxygen outlet for breathing such that the 
temperature is no more than 35  deg.F less than the cabin ambient 
temperature or 32  deg.F (whichever is greater) under the conditions of 
the maximum demand or flow of oxygen gas for normal use of the oxygen
system.  .  .  .''
    The commenter proposes this change to address the case wherein the 
airplane may be operated unpressurized, and states that the purpose of 
the liquid oxygen system being a part of the AWACS modification is to 
provide a supply of breathing oxygen sufficient to allow operation of 
the airplane in the unpressurized mode, if this becomes necessary. The 
commenter's suggested revised wording would limit the lowest 
temperature of oxygen provided to the occupants to 32  deg.F during 
pressurized and unpressurized operations.
    The FAA concurs with the commenter. In the original Notice SC-96-8-
NM for the Boeing Model 767-27C liquid oxygen system, the FAA proposed 
that the liquid oxygen system should include provisions to ensure 
complete conversion of the liquid oxygen to gaseous oxygen. This 
provision was included to address possible hazards that would exist if 
oxygen reaching the user was too cold. The Department of the Air Force, 
commenting in response to that notice, suggested that the proposed 
special condition be revised to further require that oxygen gas 
delivered to the first oxygen outlet for breathing have a temperature 
that was not colder than 20  deg.F below the cabin ambient temperature 
under the conditions of the maximum demand or flow of oxygen gas for 
normal use of the oxygen system. The commenter did not provide a 
specific reason to support this change. However, the FAA determined 
that the proposal was acceptable because it would ensure that the 
oxygen is delivered to the user at a temperature that is not harmful. 
The FAA therefore revised paragraph ``f'' of the proposed special 
condition accordingly and issued Supplemental Notice No. SC-96-8A-NM 
for comment.
    The suggested temperature limits proposed by Boeing in response to 
the Supplemental Notice were reviewed by the FAA, including specialists 
at the FAA Civil Aeromedical Institute (CAMI). From these reviews, the 
FAA concluded that the suggested further limiting of temperature limits 
to ``no more than 35  deg.F less than the cabin ambient temperature or 
32  deg.F (whichever is greater)'' is commensurate with the basic 
intent of the proposed special condition to ensure that the oxygen is 
delivered at a safe temperature to those breathing it. The FAA 
considers that this change provides an even higher level of safety than 
the original proposal. As it affects only the applicant who requested 
the change, further noticing of the special conditions is not 
considered necessary.
    The remainder of the special conditions for the 767-27C liquid 
oxygen system installation are adopted as proposed.
    As discussed above, these special conditions are applicable 
initially to the Boeing Model 767-27C airplane. 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, 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 one model series of airplane. 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 767-27C airplanes 
modified to an AWACS configuration:
    a. The liquid oxygen converter and other oxygen equipment shall not 
be installed where baggage, cargo, or loose equipment are stored 
(unless items are stored within an appropriate container which is 
secured or restrained by acceptable means).
    b. The liquid oxygen converter shall be located in the airplane so 
that there is no risk of damage due to an uncontained rotor or fan 
blade failure.
    c. The liquid oxygen system and associated gaseous oxygen 
distribution lines should be designed and located to minimize the 
hazard from uncontained rotor debris.
    d. The flight deck oxygen system shall meet the supply requirements 
of Part 121 after the distribution line has been severed by a rotor 
fragment.
    e. The pressure relief valves on the liquid oxygen converters shall 
be vented overboard through a drain in the bottom of the airplane. 
Means must be provided to prevent hydrocarbon fluid migration from 
impinging upon the vent outlet of the liquid oxygen system.
    f. The system shall include provisions to ensure complete 
conversion of the liquid oxygen to gaseous oxygen. The resultant oxygen 
gas must be delivered to the first oxygen outlet for breathing such 
that the temperature is no more than 35  deg.F less than the cabin 
ambient temperature or 32  deg.F (whichever is greater), under the 
conditions of the maximum demand or flow of oxygen gas for normal use 
of the oxygen system. A LOX shutoff valve shall be installed on the 
main oxygen distribution line prior to any secondary lines. The shutoff

[[Page 53739]]

valve must be compatible with LOX temperatures and be readily 
accessible (either directly if manual, or by remote activation if 
automatic).
    g. If multiple converters are used and manifolded together, check 
valves shall be installed so that a leak in one converter will not 
allow leakage of oxygen from any other converter.
    h. Flexible hoses shall be used for the airplane systems 
connections to shock-mounted converters, where movement relative to the 
airplane may occur.
    i. Condensation from system components or lines shall be collected 
by drip pans, shields, or other suitable collection means and drained 
overboard through a drain fitting separate from the liquid oxygen vent 
fitting, as specified in Special Condition e. above.
    j. Oxygen system components shall be burst pressure tested to 3.0 
times, and proof pressure tested to 1.5 times, the maximum normal 
operating pressure. Compliance with the requirement for burst testing 
may be shown by analysis, or a combination of analysis and test.
    k. Oxygen system components shall be electrically bonded to the 
airplane structure.
    l. All gaseous or liquid oxygen connections located in close 
proximity to an ignition source shall be shrouded and vented overboard 
using the system specified in Special Condition e. above.
    m. A means will be provided to indicate the quantity of oxygen in 
the converter and oxygen availability to the flightcrew. A low LOX 
level amber caution annunciation will be furnished to the flightcrew 
prior to the LOX converter oxygen level reaching the quantity required 
to provide sufficient oxygen for emergency descent requirements.

    Issued in Renton, Washington, on October 1, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 97-27503 Filed 10-15-97; 8:45 am]
BILLING CODE 4910-13-P