Incident Overview
On March 22, 2019, at approximately 07:00 local time, a Fokker 100 aircraft with registration EP-ATG operated flight IRC840 from Mehrabad International Airport to Ilam Airport. The aircraft carried 9 crew members and 81 passengers. During approach to Ilam, the pilot encountered a technical problem preventing the landing gear from extending. Attempts to recycle the gear resulted in only the nose and left main landing gear extending. Due to Ilam Airport's operating category (CAT C) and fuel considerations, the flight was initially diverted to Kermanshah Airport, but the pilot decided to proceed to the alternate airport at Mehrabad.
Aircraft and Crew
The aircraft, a Fokker 100 (serial number 11329), was built in 1991 and powered by two Rolls-Royce TAY 650-15 engines. Its airworthiness certificate was valid. The pilot-in-command held an ATPL with Fokker 100 type rating, and the co-pilot held a CPL with the same rating. Both had completed recurrent training. No medical or behavioral issues were noted.
Landing Gear Malfunction
After reporting the problem to Mehrabad Tower, the pilot requested emergency preparations. While approaching Mehrabad, the pilot recycled the landing gear, and all gear extended normally, allowing for a safe landing at 07:50 local time. All occupants disembarked without injury.
Post-Incident Inspection
The aircraft was jacked in a hangar for landing gear testing. Operational tests revealed that the right main landing gear did not extend. Inspection of the restrictor check valve near the right main landing gear actuator found debris: parts of a cut O-ring located in the valve's orifices and the associated filter screen. The debris obstructed hydraulic fluid flow. The aircraft fuselage was undamaged, but the right-side restrictor check valve was damaged due to hydraulic system contamination.
Findings
Analysis of flight recorder data indicated delays in right main landing gear extension on previous flights, attributed to restricted hydraulic flow. The cockpit voice recorder showed no crew performance deficiencies. The investigation determined that the O-ring debris likely entered the hydraulic system during maintenance. The incident was classified as a serious incident due to the adverse situation.