What happened
On 3 December 2021, a Singapore Airlines Boeing 737-8 (MAX), registration 9V-MBF, landed at Changi Airport's Runway 02L and sustained damage to its left main landing gear. The incident occurred during a scheduled flight arriving from Phnom Penh, Cambodia. While the crew did not notice any immediate issues during the landing roll, the damage was discovered once the aircraft reached its parking bay.
Upon inspection, ground crews found that the outboard tyre of the left main landing gear had burst due to a worn-through flat spot, and the inboard tyre had also developed a flat spot. Additionally, the frame of the fixed door on the left landing gear was damaged. No injuries were reported among the 38 people on board.
The investigation
The investigation focused on why the tyres sustained such damage despite the crew's intention to perform a gentle landing. It was established that the aircraft was operating under specific Minimum Equipment List (MEL) restrictions, as both the Antiskid and Autobrake systems were inoperative. These restrictions required the crew to manually deploy speedbrakes and follow specific braking procedures to prevent tyre blowouts.
Investigators examined the sequence of events during the landing in Singapore. They found that the pilot flying attempted a gentle touchdown to minimize braking force. However, because the landing was so light, the aircraft's air/ground sensors had not yet switched to "GROUND" mode. Consequently, when the pilot selected reverse thrust, the speedbrakes failed to deploy automatically as expected.
Findings
- The primary cause of the tyre damage was wheel skidding caused by the left main landing gear wheels locking during the landing roll.
- The locking occurred because the pilot applied brake pressure before the speedbrakes were manually deployed and before the aircraft's weight was sufficiently transferred to the landing gear.
- The flight crew failed to adhere to the MEL requirements, which mandated the manual deployment of speedbrakes prior to applying brakes when the Antiskid system is inoperative.
- A misunderstanding of the aircraft's automated systems contributed to the error, as the crew expected reverse thrust to trigger speedbrake deployment automatically.
Safety action
Following the incident, the aircraft operator implemented several safety measures, including:
- Conducting remedial reinforcement training for the involved flight crew, focusing on procedures for operating with inoperative Antiskid and Autobrake systems.
- Providing simulator training sessions covering high-weight rejected take-offs and landings with inoperative systems.
- Sharing the lessons learned from this occurrence with the entire B737 pilot fleet during a safety dialogue session.