A Boeing 737-95Rwas operating a scheduled domestic flight between Delhi and Mumbai. Onboard, 120 passengers and 8 crew. The flight was uneventful and the aircraft was approaching Mumbai on its 5th flight of the day. With the co-pilot as the pilot flying the aircraft was configured as per standard operating procedures and continued its approach. The touchdown was normal (recorded G loading at touch down 1.44 G), although the aircraft floated a little before the touchdown.
The aircraft with the gear collapsed. (Source; Indian Investigation Report)
Deceleration was normal up to a speed of 58 knots, at that point a right roll of 4,57º was recorded by the DFDR (Digital Flight Data Recorder). At the same time, the crew noticed that the aircraft started to veer to the right and they heard a sound similar to a flat tire. The copilot corrected the direction with the nosewheel steering. ATC observed sparks from the righthand gear during the rollout on the runway, they informed the crew accordingly and activated the crash alarm, to which the airport fire service promptly responded. The aircraft vacated the runway and stopped on the taxiway with its tail not fully clear of the runway safety zone. The flaps were moved to 40º in anticipation of a possible evacuation. While the captain contacted the airline's operation department the APU was started and the engines shut down (left engine first, right engine second) The cabin crew was advised by the captain to keep the doors armed.
Damage to the righthand wing (Source; Indian Investigation Report)
When the fire brigade arrived at the aircraft they observed a hydraulic leak and noticed that the right-hand engine was nearly touching the ground. This information was shared with the crew and ATC. To mitigate the risk of a fire a layer of foam was sprayed over the hydraulic oil. Passenger stairs were brought to the aircraft and the passengers disembarked via the forward passenger door. None of the passengers or crew sustained any injury.
The aircraft was substantially damaged, a summarised overview, (full details available in the investigation report from the Indian Authorities investigating the accident by clicking here )
The right-hand main landing gear collapsed, partly separated from its mounts
The rIght-hand wing trailing edge damaged
The right-hand inboard (#5) flap drive and flap track damaged
The right-hand engine cowlings (fan cowl and reverser cowl damaged
The investigation revealed that the right-hand main landing gear trunnion pin due to a previously existing fatigue crack, the report details it as follows;
Fracture initiation was due to base metal heat damage as a result of abusive grinding of the chrome plate that likely occurred during the last overhaul.
The fracture originated in an area of un-tempered martinsite (UTM) on the outer diameter of the trunnion pin. The crack originated from intergranular separation, a result of hydrogen embrittlement during cadmium plate processing. The crack propagated by Trans-granular fatigue mode with ductile separation at final fracture. Multiple cracks were found near the fracture origin.
The failed trunion pin (Source; Indian Investigation Report)