The US FAA is requiring operators of Bombardier CRJ700 and CRJ900 regional jets to perform a detailed inspection of certain elements in the aircraft's main landing gear system within 50 flight cycles of 24 November, the effective date of a new airworthiness directive on the types.

The directive is the result of an investigation into two landing accidents caused by the aircraft's main landing gear failing to deploy completely, says the FAA.

Though the specific incidents are not revealed, one likely occurred on 25 September when an Atlantic Southeast Airlines (ASA) CRJ900 landed with its right landing gear fully retracted after diverting to John F Kennedy International airport in New York.

ASA flight 4951, en route from Atlanta to White Plains, New York with 60 passengers and two flight attendants, diverted to JFK after pilots received an "unsafe gear warning" and landed with its right main gear retracted. The crew and passengers, all uninjured, evacuated on the runway.

A final airworthiness directive (AD), issued today, reveals that in both cases the interference between the main landing gear (MLG) door and the MLG fairing seal had prevented the MLG door from opening, blocking the gear from extending.

In addition to the initial inspection of the MLG fairing elements, operators are required to perform repetitive inspections of the area every 600 flight hours thereafter, replacing faulty components per a Bombardier service bulletin.

Canadian safety regulators issued a parallel AD on 22 October.

Source: Air Transport Intelligence news