A Falcon 20 was on a flight training mission on this day in aviation history. After a quick refuelling stop at St Mawgan (Cornwall, UK) the aircraft had climbed to 19500 feet for the second part of the training mission.
N908FR in 1987 (© Frank C. Duarte Jr.)
The first item was a simulated decompression with an emergency descend to 12.000 feet. The second item on the program was a stall test in approach configuration, 15º of flap and the landing gear down.
After the gear was selected down no down and locked indication was shown for the left main landing gear. Several attempts were made to lower the gear using the "Abnormal Drills" procedures. Also using the manual release ring did not result in a landing gear that was down and locked. With the issue unresolved, the aircraft was in a holding pattern to burn off fuel over RNAS Yeovilton. In the meantime, the ground crew at the Royal Naval Air Station were getting the runway ready by laying a foam strip on the runway. Two flypasts of the ATC tower were performed, and a chase plane confirmed that the left main gear door was open and the left main landing gear was fully retracted. With the fuel onboard down to only 600 pounds, and extensive briefing on the applicable procedures a landing was made with Vref at 120 knots. The aircraft touched down on runway 27 on its right gear and the left-wing was held up as long as the aerodynamics allowed it. The crew kept the aircraft on the runway and the aircraft stopped in the foam covered part of the runway. During the sliding part of the landing, the left main gear was unlocked. As the crew had problems opening the emergency exit windows they vacated the aircraft through the cargo bay door after shutting the aircraft down. After the aircraft was recovered it was placed in a hangar and placed on jacks. 6 successful gear retractions and extensions were performed, also the manual release functioned normally. Several findings were made however in the landing-gear system;
There was a general lack of grease in the landing gear mechanism
The left landing gear uplock roller was seized, due to a lack of lubrication After lubrication, the uplock roller was free to move.
Moisture was found in the uplock
Main landing gear uplock in three different conditions (© aaib.gov.uk)
A check of the maintenance records revealed that the last lubrication of the landing gear was performed in December 1989. However, between January and the incident, the landing gear was washed three times.
With every wash deteriorating the condition of the grease in the different joints and bearings of the landing gear.
A normal gear cycle on a Falcon 20.
As a result of the accident, the gear lubrication schedule has been increased. The investigators (their report is available by clicking here) also looked into the issue with the emergency overwing window that could not be opened. It was discovered that on this (N registered) aircraft the handle to release the window was mounted on the fuselage structure, while on "G-"registered aircraft the release handle was mounted on the window itself.
The aircraft was repaired and returned to service.