Boeing 747-269B N707CK

Summary

On 29 July 1999 at about 23:00 local time, a Boeing 747-269B registered N707CK was involved in an accident near Anchorage, Alaska, United States. 5 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

29 July 1999 at 23:00

Classification

Accident

Location

Anchorage, Alaska, United States

Coordinates

61.1596, -149.9910

Aircraft

Boeing 747-269B

Registration

N707CK

Category

Airplane

Engines

4

Operator

Not recorded

Operating rule

Part 121: Air Carrier

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Anchorage → Bangkok

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ANC99LA099

Nobody was injured.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full 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.

Quoted verbatim from the NTSB record.