# Proposed AD FAA-2010-1095: Pratt & Whitney (PW) Models PW4074 and PW4077 Turbofan Engines

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 2011-14-07
- Products: Pratt & Whitney Division
- Product type: Engine
- Action: Notice of proposed rulemaking (NPRM).
- Published: February 24, 2012, 77 FR 11017
- Comments due: April 24, 2012
- Became: [AD 2011-14-07](https://openairdocs.org/ad/2011-14-07)
- Docket: FAA-2010-1095 (https://www.regulations.gov/docket/FAA-2010-1095, where comments are filed)
- Project: 2009-NE-40-AD
- FR document: 2012-4286
- Official PDF: https://openairdocs.org/files/sha256/ec/2b/ec2bf51f2dc9c692fdf9e4d685622eb5ad079257756b2c4f13ec068a70863bb0 (from https://www.govinfo.gov/content/pkg/FR-2012-02-24/pdf/2012-4286.pdf)
- Federal Register: https://www.federalregister.gov/documents/2012/02/24/2012-4286/airworthiness-directives-pratt-and-whitney-pw-models-pw4074-and-pw4077-turbofan-engines
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/4715776748DB44F5862579AE00502407.0001
- Page: https://openairdocs.org/proposed/FAA-2010-1095

## Summary

We propose to supersede an existing airworthiness directive (AD) that applies to all PW PW4074 and PW4077 turbofan engines. The existing AD currently requires removing the 15th stage high pressure compressor (HPC) disk within 12,000 cycles since new (CSN) or using a drawdown removal plan for disks that exceed 12,000 CSN. Since we issued that AD, we received a request from an operator that we clarify our inspection schedule for 15th stage HPC disks. This proposed AD would clarify that 15th stage HPC disks that have accumulated more than 9,685 CSN require a borescope inspection (BSI) or eddy current inspection (ECI) of the disk outer rim front rail for cracks prior to accumulating 12,000 CSN. We are proposing this AD to prevent cracks from propagating into the disk bolt holes, which could result in a failure of the 15th stage HPC disk, uncontained engine failure, and damage to the airplane.

## Notices in this docket

- Nov 2, 2010: Notice of proposed rulemaking (NPRM). (first notice), FR document 2010-27607, comments due Jan 3, 2011 (https://www.federalregister.gov/documents/2010/11/02/2010-27607/airworthiness-directives-pratt-and-whitney-pw-models-pw4074-and-pw4077-turbofan-engines)
- Feb 24, 2012: Notice of proposed rulemaking (NPRM)., FR document 2012-4286, comments due Apr 24, 2012 (https://www.federalregister.gov/documents/2012/02/24/2012-4286/airworthiness-directives-pratt-and-whitney-pw-models-pw4074-and-pw4077-turbofan-engines)

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