McDonnell Douglas DC-9-82 (MD-82) N951AS

Summary

On 2 September 1997 at about 04:10 local time, a McDonnell Douglas DC-9-82 (MD-82) registered N951AS, operated by Alaska Airlines, was involved in an accident near Seattle, Washington, United States. 116 people were on board and 19 had minor injuries. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

2 September 1997 at 04:10

Classification

Accident

Location

Seattle, Washington, United States

Nearest airport

Seattle-Tacoma Intl (KSEA)

Coordinates

47.4397, -122.2794

Aircraft

McDonnell Douglas DC-9-82 (MD-82)

Registration

N951AS

Category

Airplane

Engines

2

Operator

Alaska Airlines

Operating rule

Part 121: Air Carrier

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Los Angeles → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Night/Dark

NTSB number

SEA97FA202

19 people had minor injuries.

fatigue failure of the nose landing gear upper lock link, due in part to reduced strength after the manufacturing process was changed from forged to machined plate stock; and inadequate non-destructive inspection process for testing the link.

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

Read the full NTSB narrative

During the landing roll-out, the nose landing gear collapsed. Examination of the nose landing gear revealed the nose gear upper lock link, PN 3914464-503, had failed, and had separated into two pieces. The link, which was subject to recurring non-destructive testing every 5000 cycles (per AD 97-02-10), had an eddy current inspection by the operator, 1075 cycles before the accident. The link was one of a series manufactured from plate stock, rather than being forged. Due to this changed process, the lack of draft angle allowances on the machined parts reduced the load-carrying cross sectional area of the machined links to less than that of the forged links, resulting in a decrease in the overall strength. Metallurgical analysis revealed that about 10,000 major fatigue progression cycles had occurred within about .6 inches of the crack progression. Based on two major stress cycles per gear retraction/extension cycle, the crack length at 1075 cycles before the accident would have been greater than .25 inches. The inspection procedure and process provided by the airframe manufacturer did not specify removal of the upper lock link from the aircraft before recurring non-destructive tests (NDT). During the investigation, NTSB investigators and FAA inspectors observed that access to the upper lock link for NDT was limited when the part remained installed on the airplane.

Quoted verbatim from the NTSB record.