Updated: Feb 4, 2022
A McDonnell Douglas MD90 was operating a scheduled passenger flight into London Heathrow Airport on this day in aviation history in 2007. After an uneventful flight, the aircraft was vectored to an approach on one of the airport's runways.
The MD90 flight instruments (source public domain)
After selecting the gear down the green indication for the right-hand main landing gear and the nose landing gear came on, indicating these gears were down and locked. However the down and locked indication for the left main landing gear did not come on. Indicating the gear was not down and locked. However, the red indicator for an unsafe left main landing gear did not come on. (indicating that the gear is not down and locked)
The landing gear was retracted and extended again. in an attempt to achieve a down and locked indication for all landing gears. Again the left main landing gear did not indicate down and locked, nor did it indicate unsafe. A go-around was initiated and after flying the missed approach as per STAR the crew revied the situation. They reached the conclusion that the problem was most probably an indication error, as the gear did not indicate unsafe.
The incident aircraft on another approach (©Marco Dotti)
The Emergency Check List (ECL) was consulted for a landing gear unsafe. In accordance with the procedure in the ECL the landing gear was lowered using the emergency landing gear extension system. Use of the emergency "blow-down" system removes all hydraulic pressure from the landing gear system, as a result, the main landing gear doors can not be closed and they hang down. The lower edges of the main landing gear doors are fitted with a steel skid plate to prevent abrasion damage to the door structure. A second approach was started and a normal landing was made on runway 27R, the gear held, It was 'only' an indication fault. The open main gear doors came in contact with the runway tarmac as the aircraft settled on the runway causing score marks on the runway surface, without causing structural damage to the main gear doors. Two centerline lights were damaged by the open main gear doors.
The alternate gear extension on an MD90 during maintenance (not the incident aircraft)
The aircraft taxied to the gate under its own power. Once the passengers had disembarked the defect was investigated by the airlines' maintenance engineers. They confirmed a failure in the indication system for the left main landing gear. The defect was rectified and the aircraft returned to service,