# Proposed AD 99-NE-22-AD: Pratt & Whitney PW4000 Series Turbofan Engines

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 99-17-16
- Action: Notice of proposed rulemaking (NPRM).
- Published: April 22, 1999, 64 FR 19726
- Comments due: May 24, 1999
- Became: [AD 99-17-16](https://openairdocs.org/ad/99-17-16)
- Docket: 99-NE-22-AD
- FR document: 99-10054
- Official PDF: https://openairdocs.org/files/sha256/05/2b/052b84d031ea5a2aab707eb85fcb9a3ae839bce41314fe53e7e43cfd0698f310 (from https://www.govinfo.gov/content/pkg/FR-1999-04-22/pdf/99-10054.pdf)
- Federal Register: https://www.federalregister.gov/documents/1999/04/22/99-10054/airworthiness-directives-pratt-and-whitney-pw4000-series-turbofan-engines
- Page: https://openairdocs.org/proposed/99-NE-22-AD

## Summary

This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Pratt & Whitney (PW) PW4000 series turbofan engines. This proposal would establish short term criteria for limiting the number of engines with potentially reduced stability on each airplane to no more than one engine, would require initial and repetitive on-wing or test cell cold takeoff high pressure compressor (HPC) stability tests, would require removal of engines from service that fail on-wing test acceptance criteria, and would allow a follow-on test cell stability test. The AD also establishes required intervals for stability testing of the remaining engine with potentially reduced stability on the airplane and requirements for reporting test data. This proposal is prompted by a report of a dual-engine HPC surge event and reports of single-engine HPC surge events during the takeoff and climb phases of flight. The actions specified by the proposed AD are intended to prevent an HPC surge event, which could result in engine power loss at a critical phase of flight such as takeoff or climb.

## Notices in this docket

- Apr 22, 1999: Notice of proposed rulemaking (NPRM). (first notice), FR document 99-10054, comments due May 24, 1999 (https://www.federalregister.gov/documents/1999/04/22/99-10054/airworthiness-directives-pratt-and-whitney-pw4000-series-turbofan-engines)

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