Iranian investigators are probing the second serious landing-gear incident involving a Fokker 100 in the space of three days after an Iran Aseman aircraft diverted to Tehran when its undercarriage only partially deployed.
The aircraft (EP-ATG) had been operating the EP840 service from Tehran to Ilam on 22 March, states the Civil Aviation Organisation.
It says that, as the aircraft conducted its approach to Ilam, the right-hand main landing-gear failed to extend.
Attempts to recycle the landing-gear were unsuccessful and the crew, believing that only the left-hand gear had deployed, aborted the landing at Ilam.
But the left-hand gear then failed to retract. The crew initially considered flying to Kermanshah but subsequently proceeded back to Tehran.
At a holding point in the vicinity of Kahrizak, south of Mehrabad, the crew tried again the release the right-hand landing-gear. The Civil Aviation Organisation says the pilots "finally" managed to deploy it, and the aircraft landed on Mehrabad's runway 29L normally at around 09:00.
None of the 81 passengers and eight crew members was injured, the organisation adds. The aircraft was jacked but the main landing-gear failed to extend when commanded.
Inspection of the hydraulic system revealed that contamination in the vicinity of filter screens and the restrictor check valve in the right-hand main gear had prevented the release of hydraulic pressure, and stopped its deployment.
"This issue has previously occurred in Fokker aircraft," says the Civil Aviation Organisation, which is advising relevant checks on the system.
European Union Aviation Safety Agency regulators issued a directive in May 2015 after two instances in which one of the main landing-gear on Fokker 100s failed to extend during approach.
Investigation showed that the filter screen of the corresponding restrictor check valve was broken and debris inside the restrictor check valve was blocking the return flow from the affected landing-gear actuator.
"Additional inspection of the fleet of the operator involved revealed more damaged or failed filter screens," EASA stated at the time, an instructed operators to follow Fokker Services bulletins to remove affected hydraulic hoses for inspection.
Three days before the Iran Aseman incident an Iran Air Fokker 100 had sustained damage during a gear-up landing at Tehran Mehrabad, after both of its main landing-gear assemblies failed to deploy.
Cirium Fleets Analyzer lists the Aseman aircraft as a 1991 airframe, like the Iran Air jet, adding that it was originally delivered to Braathens in 1994, and operated by various carriers including Gill Airways, Eujet and Brit Air.