AD 2020-13-06 Prompted By Material Microstructure Anomaly

The FAA is adopting a new airworthiness directive (AD) for certain Pratt & Whitney Canada Corp. (P&WC) PW150A model turboprop engines.

This AD was prompted by a determination by the manufacturer that certain PW150A engine high-pressure (HP) centrifugal impellers may exhibit a material microstructure anomaly that has a potential to adversely affect the low cycle fatigue characteristics of the part. This AD requires replacement of the affected HP centrifugal impellers. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective August 6, 2020.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to certain P&WC PW150A turboprop engines. The NPRM published in the Federal Register on June 24, 2019 (84 FR 29419). The NPRM was prompted by a determination by the manufacturer that certain PW150A engine HP centrifugal impellers may exhibit a material microstructure anomaly that has a potential to adversely affect the low cycle fatigue characteristics of the part. The NPRM proposed to require replacement of the affected HP centrifugal impellers. The FAA is issuing this AD to address the unsafe condition on these products.

Transport Canada Civil Aviation (TCCA), which is the aviation authority for Canada, has issued AD CF-2018-12, dated April 27, 2018 (referred to after this as “the MCAI”), to address the unsafe condition on these products. The MCAI states:

Pratt & Whitney Canada (P&WC) has determined that certain PW150A engine HP centrifugal impellers, part number (P/N) 3049127-01, may exhibit a material microstructure anomaly which has a potential to adversely affect the low cycle fatigue (LCF) characteristics of the part, resulting in a lower LCF life than currently published in the engine model's Airworthiness Limitations. The identified discrepancy was related to specific parts having been exposed to inappropriate temperature levels during the manufacturing process.

To address the subject potential material microstructure problem, P&WC issued SB 35331 Initial Issue, dated 16 March 2016, and then subsequently Revision 1, dated 3 May 2016, to recommend replacement of specific impeller serial numbers prior to the parts reaching the determined thresholds. Subsequent to the release of the SB, P&WC voluntarily initiated a fleet campaign to achieve this objective.

The actions specified by this [TCCA] AD are to ensure that HP centrifugal impellers with this potential material anomaly condition are contained in order to prevent severe engine damage and possible aeroplane damage caused by an impeller failure.

FMI: https://www.regulations.gov