ANC99LA099 · Boeing 747-269B
Boeing 747-269B · Accident: total loss of engine power (mechanical failure) en route
From Ted Stevens Anchorage International Airport (ANC) to Don Mueang International Airport (VTBD)
Event
- NTSB case
- ANC99LA099
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- Airline
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Boeing 747-269B
- Aircraft type
- Boeing 747
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N707CK
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Ted Stevens Anchorage International Airport (ANC), Anchorage, AKTo Don Mueang International Airport (VTBD), Bangkok
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 121: Air Carrier
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route · climb to cruise
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Total loss of engine power (mechanical failure)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Turbine assembly, shroud › Penetrated
- Turbine assembly, turbine blade › Failure
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
During climbout, the Boeing 747 crew noted a loud 'thump,' followed by a change in the number three engine instrument indications. One crewmember noted there was a fist-sized hole in the side of the engine cowling. The captain shut down the number three engine, returned to the departure airport, and landed without further incident. A postlanding inspection revealed that the inboard aileron sustained substantial damage. Disassembly of the engine revealed that there were eleven 2nd stage turbine blades that were fractured in the midspan area, and one other 2nd stage turbine blade that was elongated and necked down in the midspan area with most of the shroud tip rubbed off. The turbine exhaust case had a 16 1/2-inch long hole between the case front flange and the front mount rail. Engine service records revealed that when the turbine exhaust case was overhauled, Airworthiness Directive (AD) 96-25-10 was complied with by incorporating Chromalloy Anniston Division's, Supplemental Type Certificate (STC) SE00047AT-D. The intent of STC SE00047AT-D is to comply with FAA Airworthiness Directive (AD) 96-25-10 by increasing the wall thickness of the turbine exhaust case, thus providing enhanced containment capabilities in the event of an internal engine failure. A portion of the turbine exhaust case was sent to the NTSB Materials Laboratory for examination. A Safety Board metallurgist confirmed that both the hardness and microstructure were consistent with design specifications stipulated in Chromally Anniston Division's STC.
Probable cause
The failure of a turbine blade, and subsequent penetration of the shroud (containment ring). A factor associated with the accident was the FAA's insufficient design standards/requirements addressed in an FAA Air Worthiness Directive, which called for a strengthened containment ring. The failed containment ring was in compliance with the Air Worthiness Directive.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ANC99LA099
- Event ID
- 20001212X19142
- Case number
- ANC99LA099
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 4cb3233b94e2ae38207721cf2a7bcc49858d73b9e75a3215eb82e48739dec085; retrieved 2026-09-18T16:54:56.661Z.