[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]
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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.
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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]
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