# NTSB NYC91IA133: Boeing 747SP, N148UA, Churchville, NY, April 29, 1991

- Type: NTSB incident investigation
- Classification: Incident · No injuries · Incident investigation · Final report
- Date: April 29, 1991, 12:00 local (16:00 UTC)
- Place: Churchville, NY
- Coordinates: 43.100536, -77.87957 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=43.1005&lon=-77.8796&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 102 uninjured
- Status: Completed, report May 3, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 36814
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=NYC91IA133
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/36814/pdf
- Page: https://openairdocs.org/ntsb/NYC91IA133

## Probable cause

A FAILURE OF THE SIXTH ROTATING AIRSEAL WHICH LED TO AN UNCONTAINED ENGINE FAILURE.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Loss of engine power, cruise
  - turbine assembly,air seal - failure,partial (cause)
  - 1 engine

## Analysis

THE BOEING 747SP HAD JUST LEVELED OFF AT FL350 AND WAS ACCELERATING FROM M.81 TO M.85.  DURING THE ACCELERATION, A VIBRATION WAS FELT IN THE COCKPIT AND CABIN.  NO ABNORMAL ENGINE READINGS WERE OBSERVED.  THE VIBRATION LASTED FOR ABOUT 2 MINUTES AND WAS FOLLOWED BY A LOUD BANG HEARD IN THE COCKPIT.  THE NUMBER TWO ENGINE REVEALED A FAILED SIXTH ROTATING AIRSEAL.  METALLURGICAL EXAMINATION OF FAILED AIRSEAL SHOWED FEATURES TYPICAL OF OVERSTRESS WITH NO INDICATION OF PREEXISTING CRACKS.

## Aircraft

- Registration: N148UA (not matched to a registry record)
- Reported make and model: BOEING 747SP
- Category: Airplane
- Serial number: 21648
- Engines: P&W JT9D-7ASP turbo fan
- Damage: Minor damage
- Flight: Part 121
- Operator: United Airlines
- Registered owner: United Airlines
- Airworthiness certificate: Standard, Transport
- Last inspection: Continuous airworthiness, January 2, 2000
- Departed: EWR, NEWARK, NJ
- Destination: TYO, TOKYO, JAPAN
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 52; airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 16,202 total, 51 in the last 90 days

## Weather

- Conditions: Visual (VMC), Day

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Incident 19910429019829I](https://openairdocs.org/incident/19910429019829I), Apr 29, 1991: Boeing 747SP21, Newark, NJ, Minor damage. NR2 engine vibrating. Secured it and returned. Engine had uncontained failure of turbine section.

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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