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an uncontained engine failure at cruise of approximately 1x10-7 per engine hour. New engine
designs appear to reduce this probability by an order of magnitude. We found, as noted in the
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MSHWG report on § 25.841(a), that no fatalities from hypoxia were due to in-flight rapid
decompression events as envisioned by Amendment 25-87. The data indicate that
decompression is not a significant cause of fatalities. It is because these events are so rare that
the FAA considers the risk to be acceptable.
In addition, Airbus provided the FAA with proprietary data from its analysis of uncontained
engine rotor failures and the size and number of holes in the fuselage resulting from such failures.
Using historical data, the petitioner performed decompression analysis for several scenarios.
Airbus analyzed the probability of uncontained engine rotor failure and of penetration of the
fuselage of the A380 from fragments of various sizes resulting from such failures. This analysis
was used to assess the threat of such an event to occupants of the airplane.
The FAA concurs with the petitioner that uncontained engine rotor failures are rare events, and
this consideration had a bearing on the granting of the exemption. Our analysis in this case is in
contrast to our analysis of an earlier petition for exemption from a different applicant for an
airplane with a lower cruise altitude. The petition submitted by the previous applicant included
estimates of the probability of occurrence of an uncontained engine rotor failure. In that case,
the altitude excursion above 40,000 feet was less than 1,000 feet. We concluded that the risk
associated with exposure of the occupants to the slightly higher altitude was essentially the same
as the risk of exposure at 40,000 feet. In other words, the risk from exposure at altitude was
essentially the same with or without the grant of the exemption. Therefore, the rarity of
uncontained engine rotor failures did not significantly enter into consideration regarding the
previous grant of exemption.
4. Holes from uncontained engine rotor failure
The FAA evaluated both the Airbus approach and the method suggested by one of the
commenters for determining the size of holes in the fuselage and/or wings caused by uncontained
engine rotor failure. We concluded that each method makes some assumptions which one could
question. However, this issue is not of great significance since the FAA required Airbus to
assume a failure which produced a very large hole in the fuselage, causing a sudden
decompression. Airbus evaluated this scenario and provided the results in its petition.
5. Use of supplemental oxygen
In terms of the comment that “…were the FAA to allow this exemption, we strongly urge the
FAA to do so only after ensuring that each and every one of the following MSHWG
recommendations (Reference 2, pp. 41-42) are first incorporated into the A380 design and
operational plan….” As discussed below, the FAA has analyzed the Airbus petition in the
context of those recommendations, the part 25 requirements pertaining to supplemental oxygen,
and certain technical standards for supplemental oxygen equipment.
Section 25.1441(d) requires approval of oxygen equipment for airplanes that are approved to
operate above 40,000 feet altitude. Section 25.1443 specifies the minimum mass flow of
supplemental oxygen for flight crew and passenger oxygen systems up to a cabin altitude of
40,000 feet. Part 25 does not contain standards for oxygen systems above 40,000 feet. However,
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FAA Technical Standard Orders (TSOs) provide requirements for diluter demand pressure
breathing regulators (TSO-89) and demand oxygen masks (TSO-78) up to 45,000 feet. In
addition, the Society of Automotive Engineers (SAE) Standard AS 8027 provides specifications
for diluter demand pressure breathing regulators up to 45,000 feet. It is the FAA’s understanding
that no diluter demand pressure breathing regulators available for commercial airplanes meet all
the requirements of TSO-89 or AS 8027.
As part of the validation work on the A380-800, the FAA requested that Airbus propose
performance standards for fixed and portable oxygen systems for the flight crew, flight
attendants, and passengers to use between 40,000 and 43,000 feet cabin altitude. We also
requested that Airbus substantiate the adequacy of the proposed performance standards. Airbus
provided test results and analysis which substantiate that the proposed standards for oxygen
pressure breathing equipment would adequately protect the flight crew in the event of
decompression to 43,000 feet.
Flight crew pressure breathing equipment requires training to ensure effective use. Pressure
　
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