Tue, Apr 27, 2010
Aims To Establish An International, Uniform, Design And Test
Requirement
The FAA has published an NPRM in the Federal Register to
solicit comments on the proposed establishment of uniform rotor
overspeed design and test requirements for aircraft engines and
turbochargers certificated by the FAA and the European Aviation
Safety Agency (EASA).
The proposed rule would also establish uniform standards for the
design and testing of engine rotor parts in the United States
and in Europe, eliminating the need to comply with two differing
sets of requirements. The proposed rule would improve safety by
clarifying existing overspeed requirements for aircraft turbine
engine rotor parts.
The FAA tasked the Aviation Rulemaking Advisory Committee
through its Engine Harmonization Working Group to review
existing regulations and recommend changes that would eliminate
differences between the U.S. and European engine certification
standards by harmonizing to the higher standards. This proposed
rule is a result of this harmonization effort.
This proposed rule would harmonize rotor overspeed
requirements found in 14 CFR part 33 with EASA CS–E
specifications in CS–E 840, Rotor Integrity. The proposed
rule would improve safety by establishing one harmonized standard
requiring:
- Rotors be designed with a burst/ failure speed that exceeds the
certified operating speeds.
- Burst speeds to exceed overspeed conditions that can result
from the failure of other engine components.
- Limits on the amount of rotor growth or damage that results
from an overspeed.
The proposed rule would harmonize U.S. requirements with EASA
by:
- Changing the current FAA overspeed design margin from 115 to
120 percent of maximum permissible speed for all engine ratings
except OEI ratings of less than 21.2 minutes.
- Changing the current FAA overspeed design margin from 100 to
105 percent for operating conditions associated with multiple
failures.
- Introducing similar OEI overspeed design requirements.
- Requiring new similar rotor pass/ fail design criteria.
- Requiring similar overspeed margin requirements.
- Allowing the use of validated structural analysis tools to
demonstrate compliance.
- Requiring that validated structural analysis tools be
calibrated to actual overspeed tests of similar rotors.
Allowing engine test durations of less than 5 minutes for
failure conditions for which a 5-minute duration is not
considered realistic.
Comments are due by July 26th, 2010.
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