On October 3, 1987, a Fokker F-28-MK-1000 (registration N288N) was involved in an aviation accident near Baltimore, MD. Investigators recorded the probable cause as: The use of a wrong washer with a bolt during installation of the downlock mechanism, resulting in a permanent reduction below design clearance between the downlock plunger and its internal bearing, leading to failure of the nose gear to lock down. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A nose gear failed to lock down, leading to a main gear only landing on the first flight after a newly overhauled nose gear was installed. Investigation found a wrong washer used in the downlock mechanism caused clearance reduction and scoring.
Incident
The aircraft performed a landing on its main gear only after the nose gear failed to lock down. This was the first flight following the installation of a newly overhauled nose gear.
Investigation Findings
Examination determined that during the installation of the nose gear, a wrong washer was used with a bolt to assemble part of the downlock mechanism. Before this error was corrected, the incorrect washer resulted in an undetected permanent reduction in the design clearance between the downlock plunger and its internal bearing.
Post-Landing Examination
After the landing incident, inspection of the downlock mechanism revealed scoring on the downlock plunger and its internal bearing. No other contributing factors were identified in the source.
Probable cause
The use of a wrong washer with a bolt during installation of the downlock mechanism, resulting in a permanent reduction below design clearance between the downlock plunger and its internal bearing, leading to failure of the nose gear to lock down.
