The FAA is fast-tracking a mandate for Airbus A320-family main landing gear door system checks to prevent the combination of failures that recently forced a Wizz Air A320 to make an emergency landing without its left main gear extended.

The airworthiness directive (AD), published Thursday, gives operators of some 850 U.S.-registered Airbus narrowbodies until Sept. 6 to check for certain combinations of landing gear control interface units (LGCIUs) and main landing gear (MLG) door actuator part numbers. Aircraft with the identified combinations must undergo MLG door sequence inspections, or either modify the LGCIUs or install newer actuators. Faulty actuators must be replaced immediately.

The failures stem from deteriorating main landing gear (MLG) door actuator damping and retaining rings, which release metallic debris into the actuators.

Early signs of the problem include a slow gear door sequence. While it doesn’t disrupt the gear operation, the slow door opening is supposed to generate specific Centralized Fault Display System (CFDS) messages that “that are necessary to mitigate risks  with failure of MLG extension or down-locking,” FAA says in its AD.

The actuator problems were first reported in 2006. In 2008, Airbus introduced a new actuator, but the problem persisted. In 2011, the European Aviation Safety Agency (EASA) ordered operators to monitor CFDS messages and, if specific ones were generated indicating slow door sequences, verify the MLG doors were working correctly. 

In the recent Wizz Air incident, Flight 3141 was on approach to Roma-Ciampino Airport from Bucharest-Henri Coanda International Airport on June 8 when the crew received a warning that its left main gear was not down and locked. After a failed recycle attempt, the crew resorted to the manual extension procedure, which also failed.

The crew then diverted to Roma-Fiumicino Airport and made an emergency landing, shutting down its left engine just before it touched the runway. All 165 passengers and seven crewmembers evacuated safely.

Investigators discovered the Wizz Air plane’s left MLG door actuator didn’t fully extend, preventing the door from opening. The left main gear was caught in the door. When investigators removed the jammed actuator, “the door fully opened and the gear correctly extended and locked,” a report from Italy’s ANSV says.

Analysis of the Wizz Air CFDS revealed no previous gear door fault messages.

In probing the incident, Airbus discovered that airplanes outfitted with a certain combination of LGCIUs and actuators were “masking” the relevant CFDS messages, creating the possibility of actuators unknowingly getting worse.

Investigators determined that, left unchecked, the debris build-up can restrict an actuator enough to delay gear deployment, which automatically triggers a flight crew warning that the gear is not down and locked. When pilots switch to the manual gear extension mode, a faulty actuator could keep the gear door from “free-falling” open and the gear from extending, even if the crew follows the correct procedures.

Airbus issued an All-Operators Telex on June 24, alerting operators to the newly discovered CFDS anomaly and potential ramifications. EASA’s emergency directive followed a day later.

FAA’s AD is based on the EASA directive. The problem’s urgency prompted FAA to go directly to final AD status without prior public comment.