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aid/affect the aircraft occupants in the event of a high altitude explosive decompression.”
ALPA adds, “Passenger cabin masks are not designed to provide protection against hypoxia
above FL 400 (40,000 feet). These masks provide no protection against DCS [decompression
sickness]. Before considering granting this exemption, [we] recommend study of the level of
protection provided by current masks above FL400.”
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4. Various statements in Petition for Exemption
The commenters opposing a grant of the petition, i.e., AFA and ALPA, also took issue with
various statements in the petition. Although the FAA reviewed and considered all of these
comments, we responded explicitly only to those that were directly pertinent to our analysis. For
example, AFA says that a certain conclusion stated by Airbus is based on a certain assumption.
The FAA agrees that making a different assumption would lead to a different conclusion, but we
do not find that the statement in the petition directly affects our analysis.
The FAA has carefully considered all the comments received and has taken them into account in
our analysis of the Petition for Exemption submitted by Airbus. We acknowledge the need for
additional research on the effects of exposure to high altitude cabin pressure—particularly
research about its effects on people of various ages and those with circulatory, respiratory, or
other diseases. We also acknowledge the need for validation of the DEI methodology
recommended in the MSHWG’s Final Report and in our Interim Policy on Amendment 25-87
Requirements. Even though the FAA plans to conduct additional research on this subject, we
find that sufficient data, including service history, is available to support this proposed
exemption for the Model A380-800. In the following section, we consider comments on the
Airbus petition in greater detail.
The FAA’s Analysis of the Petition
1. Need for exemption
Airbus requests relief from § 25.841(a)(2)(i) which specifies that cabin pressure altitude may not
exceed 25,000 feet for more than 2 minutes after decompression from any failure condition not
shown to be extremely improbable. A grant of exemption from this regulation would allow the
Model A380-800 to take longer than 2 minutes to descend from 43,000 feet to 25,000 feet after
such decompression.
Airbus also requests relief from § 25.841(a)(2)(ii) which specifies that cabin pressure altitude
may not exceed 40,000 feet for any duration after decompression from any failure condition not
shown to be extremely improbable. A grant of exemption from this regulation would allow the
Model A380-800 cabin pressure altitude to exceed 40,000 feet after such decompression.
Based upon data received from Airbus, the FAA’s analysis confirms that the design of the
A380-800 meets the requirements of § 25.841(a)(2)(i) and (ii) for all system and structural
failures but not for all types of engine failures. For some uncontained engine rotor failures that
result in pressure vessel penetration by fragments, the design of the A380-800 does not meet the
requirements of § 25.841(a)(2)(i) and (ii). A grant of exemption from this regulation would
allow the Model A380-800 to operate up to 43,000 feet, which could briefly expose cabin
occupants to this altitude in the event of a worst-case decompression.
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Finally, Airbus requests relief from § 25.841(a)(3) which requires that an airplane manufacturer
consider fuselage structure, engine, and system failures when evaluating the cabin pressure
altitude following a decompression due to one of these failure events. As noted in the preamble
to this regulation,
“Possible modes of failure to be evaluated include malfunctions and damage from
external sources such as tire burst, wheel failure, uncontained engine failure, engine fan,
compressor or turbine multi blade failure, and loss of antennas….”
FAA’s analysis shows that Airbus did include these failures in its analysis. Therefore, the
petitioner complies with § 25.841(a)(3), obviating the need for an exemption from it.
2. Conformance with applicable FAA policy
The FAA reviewed this petition in the context of the MSHWG Final Report on § 25.841(a)(2)
and (a)(3) and of our Interim Policy on Amendment 25-87 Requirements. The Interim Policy
applies only to those decompression events which are due to uncontained engine rotor failure.
The basis of the Interim Policy is data from research on the response of humans and other
primates to changes in ambient pressure. Evaluation of this data indicates that there is a direct
correlation between the alveolar partial pressure of oxygen time integral and the likelihood of
　
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