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NTSB Report
April 29, 1991 · Boeing 747SP · N148UA
Churchville, NY
Overview
Report Status
Probable Cause
Event Type
Incident
Date
April 29, 1991
Injury Outcomes
No injuries (102 uninjured)
Location
Churchville, NY
Aircraft
Boeing 747SP
Tail Number
N148UA
Operator
United Airlines
Injuries
None
Aircraft Damage
Minor
NTSB Number
NYC91IA133
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.
NTSB Probable Cause
A FAILURE OF THE SIXTH ROTATING AIRSEAL WHICH LED TO AN UNCONTAINED ENGINE FAILURE.
Full Narrative
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.
Flight
Event TypeIncident
Event Time12:00 EDT
Nearest Airport0nm N
Runway0
Flight Plan FiledIFR
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftBoeing 747SP
Tail NumberN148UA
Aircraft CategoryAir
DamageMinor
OperatorUnited Airlines
Operating RulePart 121
Engines4
Engine TypeTurbofan
Engine DetailsP&W · JT9D-7ASP · Turbofan
People & Injuries
Injury SummaryNo injuries (102 uninjured)
Fatal0
Serious0
Minor0
Uninjured102
Total102
Crew 1Age 52 · First Class
Conditions
ConditionsVMC
LightDaylight
WindCalm
CeilingNone
Temperature / Dew Point0 C / 0 C
Altimeter0
Weather SourcePILO