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.

FMI: http://edocket.access.gpo.gov/2010/pdf/2010-9588.pdf