A broken nose water spray deflector prevented the pilots of a Lion Air Boeing MD-90 from extending the aircraft's landing gear in February 2009 and forced them to make an emergency landing.
The deflector itself broke because of a pre-existing crack, which led to its left side getting stuck at the nose landing gear bay structure, says Indonesia's National Transport Safety Committee in its final report into the incident.
The aircraft, with the registration PK-LIO, was on a scheduled service from Medan's Polonia airport to Batam's Hang Nadim airport. Its 156 passengers and six crew members were not injured in the incident.
The final report says that the right side of the water spray deflector was detached because of a crack at the centre deflector and that the attachment flange was broken. A dark coloured portion at the fracture indicated a pre-existing crack, adds the NTSC.
"The evidence at the pre-existing crack indicated that extraneous upward bending acted on the flange. The evidence at the right deflector, that is dent and wear at the rubber liner, suggested that an upward force could have acted at the deflector. The cause of the damage, [the] upward bending of water spray deflector, could not be accurately determined. The nose gear could not be put down because of the part of the damage deflector obstructed the nose gear," says the NTSC.
On that flight, the pilots noticed that a red light indicating the landing gear was illuminated after take-off, while trying to retract the landing gear. They recycled the landing gear and the subsequent indication was that it was in the "up and locked" position. They then continued on to Batam.
During the final approach, the red light nose gear indicator was illuminated again. The pilot in command decided to conduct a go around and hold to perform the emergency checklist, and to try to extend the nose landing gear. The landing gear failed to extend despite several attempts.
The pilots then made an emergency landing on runway 04 without the nose landing gear extended. The aircraft stopped on the centre line, and the passengers and crew were evacuated via the left front door escape slide.
The NTSC says that upon investigations, the damage to the water spray deflector showed that there was a fatigue crack that grew from its attachment hole. The nose gear could not be extended because of the damage to the deflector, which moved out to the nose wheel structure and blocked the gear.
The agency did not issue any new recommendations in its final report. In its preliminary report in April 2009, it recommended that Indonesian MD-90 operators review the nose landing gear inspection procedures to ensure that the spray deflector is checked for cracks at each nose wheel tire change.
It also asked the Directorate General of Civil Aviation to mandate an inspection requirement specifying the procedures and intervals, in order to detect cracks in the nose landing gear spray deflector. It also recommended an inspection on the flange to detect any cracks.