# Airworthiness Directives; Pratt & Whitney PW4000 Series Turbofan Engines
> **Rule** · Final rule. · Published 1998-11-13 · Effective 1999-01-12 · 63 FR 63391
## Document
- **Document number:** 98-30320
- **Category:** airworthiness
- **Manufacturer:** Pratt & Whitney PW4000 Series Turbofan
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 63 FR 63391
- **Publication date:** 1998-11-13
- **Effective date:** 1999-01-12
- **FAA docket:** Docket No. 97-ANE-53-AD
## Abstract

This amendment adopts a new airworthiness directive (AD), applicable to certain Pratt & Whitney (PW) PW4000 series turbofan engines not incorporating modifications described in certain PW service bulletins listed in the applicability section, that requires high pressure compressor (HPC) blade tip grinding of the rotor assembly, installation of aluminum oxide coated HPC blade tips in stages 9 through 12, modification of HPC 8th through 14th stage stators, incorporation of 1st stage high pressure turbine (HPT) vanes with increased airflow area which also requires additional HPT hardware modifications, and incorporation of HPC 13th-15th stage zirconium oxide blade tips. This amendment is prompted by reports of HPC surge caused by excessive HPC rear stage rotor-to-case clearance. The actions specified by this AD are intended to prevent HPC surge, which can result in engine power loss at a critical phase of flight such as takeoff or climb.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/1998/11/13/98-30320/airworthiness-directives-pratt-and-whitney-pw4000-series-turbofan-engines)
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