[Federal Register Volume 62, Number 139 (Monday, July 21, 1997)]
[Proposed Rules]
[Pages 38945-38948]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-19104]


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 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 62, No. 139 / Monday, July 21, 1997 / 
Proposed Rules  

[[Page 38945]]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-135; Notice No. SC-96-8A-NM]


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

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Supplemental notice of proposed special conditions.

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SUMMARY: This notice revises an earlier proposal for special conditions 
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. This action revises the original proposal to address 
certain recommended additional requirements for the LOX system. The 
revised 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.

DATES: Comments must be received on or before August 11, 1997.

ADDRESSES: Comments on this proposal may be mailed in duplicate to: 
Federal Aviation Administration, Office of the Assistant Chief Counsel, 
Attention: Rules Docket (ANM-7), Docket No. NM-135, 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-135. 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:
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: 

Comments Invited

    Interested persons are invited to participate in the making of 
these proposed special conditions by submitting such written data, 
views, or arguments as they may desire. Communications should identify 
the regulatory docket or notice 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 
before further rulemaking action is taken on these proposals. The 
proposals contained in this notice may be changed in light of 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 notice must submit with those 
comments a self-addressed, stamped postcard on which the following 
statement is made: ``Comments to Docket No. NM-135.'' The postcard will 
be date stamped and returned to the commenter.

Background

    On November 21, 1996, the FAA published notice in the Federal 
Register (61 FR 59202) of proposed special conditions for Boeing Model 
767-27C airplanes modified to an AWACS configuration. The special 
conditions are proposed requirements for design and installation of a 
liquid oxygen (LOX) system. These special conditions are considered 
necessary to provide the appropriate design and installation criteria 
required to assure safety of the LOX system.
    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 has 
revised special conditions f. and m. By this notice, the comment period 
is reopened to allow interested persons to comment on the additional 
requirements.

Discussion of Comments

    One commenter, the Department of the Air Force, Headquarters 
Aeronautical Systems Center, responded to the request for comments, 
providing the following comments and recommended additions/changes to 
the identified paragraphs of the proposed special conditions. Those 
recommended additions/changes are prompted by U.S. Air Force past 
experience with LOX systems in other airplanes. The proposed special 
conditions addressed by the comments, the relevant comments, and the 
FAA's assessment and conclusions are as follows:
    Special Condition 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.
    The commenter agrees with the special condition but has additional 
concerns. The commenter advises that the Department of the Air Force 
would require inspection of the compartment or zone in the airplane 
which contains the LOX converter and heat exchanging equipment to 
ensure that no buildup of flammable vapors may occur. The commenter 
states minor leakage of LOX systems fittings is a common problem 
because of the cold LOX and gas temperature effects on the metal 
fittings. The commenter further states that the buildup of gaseous 
oxygen in combination with flammable vapors in an airplane compartment 
is a serious concern, and therefore recommends that the compartment 
have adequate ventilation and smoke detectors that will alert the 
flightcrew in case of fire. If the LOX converter is located in the 
lower lobe, the commenter recommends that inflight access to this 
compartment be provided. The commenter further states that for USAF 
AWACS airplanes they have also recommended that safety equipment, 
including fire extinguisher(s) and portable protective breathing 
equipment, be provided. A recharger outlet to refill the portable 
protective breathing equipment is advisable, says the commenter, or the

[[Page 38946]]

protective breathing device should have 30 minutes minimum oxygen 
supply.
    The FAA agrees with the commenter's concern for LOX fittings and 
the buildup of oxygen in combination with flammable fluids, and access 
to the compartment containing the LOX converter. Much of these concerns 
are addressed in proposed special conditions a, c, e, g, h, and l. The 
special conditions do not require total shrouding and drainage of all 
LOX fittings, but depends on dilution of oxygen to reduce the hazard. 
In that respect, the FAA notes that the LOX converter is installed in 
the aft lower lobe of the airplane (classified as an electronic 
equipment bay), and inflight access is provided. Ventilation to this 
bay is considered adequate at 1000 to 3000 cubic feet per minute to 
preclude the hazardous accumulation of oxygen in the event of LOX 
converter or line leaks. Additionally, Sec. 25.1451 requires that 
oxygen equipment and lines be installed so that escaping oxygen cannot 
cause ignition of grease, fluid, or vapor accumulations that are 
present in normal operation or as a result of failure or malfunction of 
any system. The FAA considers that the special conditions, as proposed, 
provided adequate protection to address the concerns expressed by the 
commenter and therefore does not consider that additional requirements 
are necessary in this regard.
    The FAA does not concur with the commenter regarding the 
requirements for fire extinguishers, portable breathing equipment, and 
smoke detectors. The lower lobes of the 767-27C are classified as 
electronic equipment bays; therefore, there is no requirement to 
provide cargo bay liners, smoke detections, or fire suppression 
systems. Carry-on cargo is not permitted in either lower lobe unless it 
is stored in containers providing fire protection equivalent to that 
afforded by Class D cargo or baggage compartments. The installed AWACS 
mission/electronic equipment in these bays contains very small 
quantities of smoke-producing materials, and most are installed in 
metal cabinets. With regard to the Liquid Oxygen System located in the 
aft lower lobe, if a leak occurred in this system, a hazardous 
concentration of oxygen should be precluded by the large amount of 
ventilation (1,000 cfm minimum to 3,000 cfm with the outflow valve 
open). If a catastrophic failure of the LOX system occurred, a smoke 
detector would not reduce this danger as the smoke would occur only 
after the oxygen-enriched fire ignited.
    Special Condition c. The liquid oxygen system and associated 
gaseous oxygen distribution lines should be designed and located to 
minimize the hazard from uncontained rotor debris.
    The commenter requests specific safety practices to be followed in 
the design and installation of oxygen lines in the proximity of heat-
generating equipment and other lines carrying flammable fluid or 
electrical wires and components. The FAA does not disagree with these 
practices, but considers that the existing standards (i.e., 
Secs. 25.1451, 25.1309(a), 25.1309(b), and 25.1453) already define safe 
practices.
    Special Condition 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.
    The commenter states that this requirement is not clear. The FAA 
notes that the published version of the proposed special conditions 
contained a typographical error in that the word ``severed'' was 
printed as ``served,'' and this may have led to the confusion. This 
special condition requires that an adequate supply of oxygen be 
available to the flightcrew after cutting any line in the rotor burst 
area, and is clear with the spelling corrected. The commenter also 
notes military oxygen requirements concerning multiple oxygen supplies 
that are not relevant to this installation and states that the 
flightcrew should have control of the oxygen system. The FAA notes that 
the requirement for flightcrew control of the oxygen system is 
addressed in Sec. 25.1445(a)(2).
    The commenter further states that one flight crewmember, such as 
the flight engineer, should be designated as the crewmember responsible 
for the oxygen system. The FAA has no requirement for this in gaseous 
oxygen systems and sees no reason to require it as a special condition 
for LOX systems. The commenter states that the AWACS crewmembers should 
have oxygen dispensing and breathing equipment comparable to that 
provided to the flightcrew (i.e., pressure demand breathing equipment). 
The FAA is evaluating the crewmembers' oxygen dispensing equipment in a 
separate issue paper, and will not address it in the Special Conditions 
under discussion.
    Special Condition 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.
    The commenter concurs with the requirement for venting and draining 
the LOX converter and recommends certain safety procedures during the 
servicing of the LOX. Servicing of the LOX is not addressed in the 
airworthiness standards for transport category airplanes and is 
therefore considered beyond the scope of the notice.
    Special Condition f. The system shall include provisions to ensure 
complete conversion of the liquid oxygen to gaseous oxygen.
    The commenter agrees with the requirement to completely convert the 
liquid oxygen to gaseous oxygen, but advocates a specific requirement 
that the converted gas be no more than 20 deg. F less than cabin 
ambient temperature under the conditions of maximum demand for normal 
use of the oxygen system. The FAA agrees with the commenter and 
proposes to revise Special Condition f. to add the following sentence: 
``The resultant oxygen gas must be delivered to the first oxygen outlet 
for breathing such that the temperature is no more than 20 deg. F less 
than 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 expressed another concern regarding Special Condition 
f., which would require that the LOX converter include a ``line valve'' 
that would enable the flightcrew to shut down flow from the LOX 
converter, should a severed or broken line allow LOX to spill into the 
airplane. The FAA concurs with this concern and proposes to add the 
following sentence to Special Condition f: ``A LOX shutoff valve shall 
be installed on the main oxygen distribution line prior to any 
secondary lines. The shutoff valve must be compatible with LOX 
temperatures and be readily accessible (either directly if manual, or 
by remote activation if an automatic valve).''
    Special Condition 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.
    The commenter gives background information on a manufacturer of LOX 
converters, and advises that a rupture disk be included on the outer 
shell of the converter. The FAA does not wish to regulate a design 
solution when other designs (e.g., designing the outer shell with 
pressure capability equivalent to the inner shell) could satisfy the 
requirements of Sec. 25.1309(b).
    The commenter also discusses the advantages of dual pressure relief 
valves (failure redundancy and flow rate requirements). The FAA agrees 
that

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there is an advantage in case one valve fails, but again does not wish 
to regulate a design solution when other design implementations could 
satisfy the design requirements of Sec. 25.1309(b). The FAA also does 
not agree that two valves are required for flow rate requirements, as 
this is dependent on valve sizing.
    Special Condition k. Oxygen system components shall be electrically 
bonded to the airplane structure.
    The commenter concurs with this condition, but states that it 
requires that the system be tested to ensure that the Ohm rating from 
any component on the LOX system will not exceed that which would 
preclude static discharging. The FAA will evaluate the applicant's type 
design data to ascertain suitability of process and testing of 
electrical bonding, but does not consider it necessary to specify the 
Ohm level that the bonding is tested to in the special condition.
    Special Condition 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 (e) above.
    The commenter provided the same comments for this special condition 
as for Special Condition b. See FAA response to comments on Special 
Condition b.
    Special Condition m. A means will be provided to indicate the 
quantity of oxygen in the converter and oxygen availability to the 
flightcrew.
    The commenter agrees with the requirement for oxygen quantity 
indication and oxygen availability indication to the flightcrew and 
notes the desirability of a low level oxygen warning light due to LOX 
converter failure modes. In addition, the commenter notes that oxygen 
quantity indication should be based on volume and not on pressure, 
since the system will essentially operate at a constant pressure until 
it is nearly out of oxygen, as opposed to a gaseous oxygen system which 
depletes quantity at a linear rate (measuring pressure).
    The FAA concurs with the requirement for a low LOX level caution 
annunciation and proposes to add the following sentence to Special 
Condition m: ``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.'' The commenter also recommends a 
built-in test function so that the flight crew can ascertain that the 
low LOX level caution annunciation is functional. The FAA does not 
consider it necessary to require this as a Special Condition as it is 
adequately addressed in Sec. 25.1309(d)(4).
    As a result of these comments, and as discussed earlier in this 
document, the FAA has modified special conditions f. and m. from that 
proposed in Notice SC-96-8-NM. Public comment is therefore invited on 
these additional requirements.
    Certification flight testing of the Model 767-27C by Boeing is 
imminent. For this reason, and because a delay would significantly 
affect the remainder of the certification schedule for the Model 767-
27C, the public comment period for this supplemental notice is 
shortened to 20 days.
    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).

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: 
49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Proposed Special Conditions

    Accordingly, the Federal Aviation Administration (FAA) proposes the 
following special conditions 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 20 deg.F less than the cabin 
ambient temperature 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 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 manifold 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 system 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 (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

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to the flight crew prior to the LOX converter oxygen level reaching the 
quantity required to provide sufficient oxygen for emergency descent 
requirements.

    Issued in Renton, Washington, on July 14, 1997.
Gary L. Killion,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 97-19104 Filed 7-18-97; 8:45 am]
BILLING CODE 4910-13-M