Seattle-Tacoma Intl Airport
Aircraft Accident/Incident Report

Seattle, Washington 98188
Monday, September 1, 1997 21:10 PDT

NTSB Narrative Summary Released at Completion of Accident

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.

NTSB Probable Cause Narrative

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.

Event Information

Type of Event Accident
Event Date 9/1/1997
Event Day of the Week Monday
Time of Event 2110
Event Time Zone Pacific Daylight Time
Event City SEATTLE
Event State WASHINGTON
Event Country --
Zipcode of the event site 98188
Event Date Year 1997
Event Date Month 9
MidAir Collision Indicator No
On Ground Collision occurred ? No
Event Location Latitude
Event Location Longitude
Event Location Airport SEATTLE-TACOMA INTL
Event Location Nearest Airport ID KSEA
Indicates whether the acc/inc occurred off or on an airport On Airport
Distance from airport in statute miles --
Degrees magnetic from airport --
Airport Elevation 420
Weather Briefing Completeness Unknown
Investigator's weather source Pilot
Time of the weather observation 0
Direction of event from weather observation facility (degrees) 0
Weather Observation Facility ID
Elevation of weather observation facility 0
Distance of event from weather observation facility (units?) 0
Time Zone of the weather observation
Lighting Conditions Night/Dark
Lowest Ceiling Height 3800
Lowest Non-Ceiling Height 0
Sky/Lowest/Cloud Conditions Clear
Sky Condition for Lowest Ceiling Broken
Visibility Runway Visual Range (Feet) 0
Visibility Runway Visual Value (Statute Miles) 0
Visibility (Statute Miles) 10
Air Temperature at event time (in degrees celsius) 19
Dew Point at event time (in degress fahrenheit) 13
Wind Direction (degrees magnetic) 220
Variable Wind Indicator Unknown
Wind Speed (knots) 6
Wind Velocity Indicator Unknown
Wind Gust Indicator Not Gusting
Wind Gust (knots) 0
Altimeter Setting at event time (in. Hg) 30
Density Altitude (feet) --
Intensity of Precipitation Unknown
METAR weather report --
Event Highest Injury Minor
On Ground, Fatal Injuries 0
On Ground, Minor Injuries 0
On Ground, Serious Injuries 0
Injury Total Fatal --
Injury Total Minor 19
Injury Total None 97
Injury Total Serious --
Injury Total All 19
Investigating Agency NTSB
NTSB Docket Number (internal use) 1465
NTSB Notification Source --
NTSB Notification Date Sep 1 1997 12:00AM
NTSB Notification Time 2155
Fiche Number and/or location -used to find docket information IMAGE
Date of most recent change to record Dec 8 2000 12:34PM
User who most recently changed record dbo
Basic weather conditions Visual Meteorological Cond
FAA District Office --

Aircraft Involved

Aircraft #1

Aircraft Registration Number N951AS
NTSB Number SEA97FA202
Missing Aircraft Indicator N
Federal Aviation Reg. Part Part 121: Air Carrier
Type of Flight Plan filed IFR
Flight plan Was Activated? --
Damage Substantial
Aircraft Fire None
Aircraft Explosion None
Aircraft Manufacturer's Full Name McDonnell Douglas
Aircraft Model DC-9-82 (MD-82)
Aircraft Series Identifier DC-9-82 (M
Aircraft Serial Number 49111
Certified Max Gross Weight 149500
Aircraft Category Airplane
Aircraft Registration Class U.S. Registered/U.S. Soil
Aircraft is a homebuilt? No
Flight Crew Seats --
Cabin Crew Seats --
Passenger Seats --
Total number of seats on the aircraft 138
Number of Engines 2
Fixed gear or retractable gear Retractable
Aircraft, Type of Last Inspection AAIP
Date of Last Inspection Aug 30 1997 12:00AM
Airframe hours since last inspection --
Airframe Hours 45378
ELT Installed Unknown
ELT Activated Unknown
ELT Aided Location of Event Site Unknown
ELT Type --
Aircraft Owner Name INTEGRATED AIRCRAFT SERVICES
Aircraft Owner Street Address 10 UNION SQUARE EAST
Aircraft Owner City NEW YORK
Aircraft Owner State NY
Aircraft Owner Country
Aircraft Owner Zipcode 10003
Operator is an individual? --
Operator Name ALASKA AIRLINES
Operator Same as Owner? No
Operator Is Doing Business As --
Operator Address Same as Owner? No
Operator Street Address BOX 68900
Operator City SEATTLE
Operator State WA
Operator Country
Operator Zip code 98168
Operator Code ASAA
Owner has at least one certificate Yes - certificate holder
Other Operator of large aircraft? No
Certified for Part 133 or 137 Operation Unknown
Operator Certificate Number --
Indicates whether an air carrier operation was scheduled or not Scheduled
Indicates Domestic or International Flight Domestic
Operator carrying Pax/Cargo/Mail Passenger Only
Type of Flying (Per_Bus / Primary) Unknown
Second Pilot on Board Yes
Departure Point Same as Event No
Departure Airport Code KLAX
Departure City LOS ANGELES
Departure State CA
Departure Country
Departure Time 1821
Departure Time Zone PDT
Destination Same as Local Flt crash at destination city
Destination Airport Code KSEA
Destination City
Destination State
Destination Country
Specific Phase of Flight Landing
Report sent to ICAO? --
Evacuation occurred --
Date of most recent change to record Dec 20 2002 12:42PM
User who most recently changed record dbo
Since inspection or accident --
Event Location Runway Number and Location 16L
Runway Length 11900
Runway Width 150
Sight Seeing flight No
Air Medical Flight No
Medical Flight --