A 25-year-old Fokker 100 (Fokker 28 Mark 0100) was operating a scheduled passenger flight between Tehran-Mehrabad Airport and Mashad Airport, both in Iran. On board the aircraft, a crew of seven (2 flight crew and 5 cabin crew) and 97 passengers.
The aircraft in its final position (Source & © Tayyarehblogfa.com)
The take-off from runway 29L at Mehrabad Airport, at 13:08 UTC, and the subsequent flight to Mashad Airport were uneventful. At approximately 10 miles from the landing, as the crew configured the aircraft for landing, the Left Main Landing Gear unsafe indication came on. The Pilot in Command informed ATC of the issue and requested a missed approach and vectors to a holding point for completion of the required checklists. When in the holding the crew completed the relevant checklists but was unable to extend the Left Main Landing Gear. Also, the landing gear alternate selection did not get the Left Main Landing Gear in the down and locked position. A total of five attempts were made to lower the left Main Landing Gear, all were unsuccessful.
A MAYDAY call was made to ATC and an emergency was declared, the aircraft remained in the holding to burn off fuel. At 16:01 UTC the flight indicated to be ready for landing, subsequently, the flight was cleared to land at Runway 31R of Mashad, with the left Main Landing Gear indication still unsafe.
The aircraft before recovery (Source & © Tayyarehblogfa.com)
During the landing, the crew initially managed to keep the aircraft on the runway but as the speed decayed the aircraft veered to the left and came to a stop between Runway 31R and Runway 31L. There were no injuries to the occupants of the Fokker 100. Damage to aircraft as a result of the landing was substantial;
Right-hand landing landing gear wheels
Left-wing trailing edge, especially the flaps
Left-wing lower surface
Left-hand main landing gear doors damaged
Additional damage occurred during the recovery of the aircraft, as the hoisting equipment ( slings) was not strong enough, causing the aircraft to drop onto a jack that was located under the wing. This resulted in additional extensive additional damage to the left-hand wing.
The aircraft after the bodged recovery attempt (Source and © AAIB)
The Civil Aviation Organization Aircraft Accident Investigation Board (AAIB) of Iran was alerted, and an investigation into the accident was started. During the investigation, it became apparent that a check valve in the hydraulic system of the Left Main Landing Gear contained foreign materials (similar to blasting particles). The screen filter on the check valve was damaged and partly blocked. The nozzle of the check valve was also blocked with foreign materials. This caused a restriction in hydraulic flow and failure of the Left Main Landing Gear to get in the down and locked indication.
The contaminated restrictor check valve (Source & © AAIB)
It was discovered that the foreign debris entered to hydraulic system while performing a maintenance task for a one-time inspection of the Restrictor Valve and hydraulic hose from the left landing gear actuator.
The AAIB concluded its report stating that the main cause of this accident was “entering foreign contamination to the hydraulic system by “maintenance activities during C Check“ which caused damage and a blockage of hydraulic flow in the restrictor check valve. The screen filter near the hydraulic restrictor check valve was damaged by the reflected force of Pollution and sediment available in the hydraulic system between and caused blockage of the nozzle downstream to down lock LH landing gear mechanism.
Contributing factors were;
Insufficient surveillance on maintenance operation of aircraft.
Lack of enough experience for Qeshm Air maintenance personnel.
Several safety recommendations were made by the AAIB, they can be found in the AAIB accident investigation report which can be accessed by clicking on the .pdf file below.