Accident Overview
On July 1, 2019, a Boeing 737-800 experienced a runway excursion during landing at Mumbai airport. The aircraft was operating the fifth flight of the day and the second for the flight crew, who had earlier flown from Mumbai to Jaipur. The incident occurred on the return leg from Jaipur to Mumbai during the late evening. Weather conditions at the time included moderate to heavy rain, with visibility reported at 2100 meters. The wind was from 090 degrees at 12 knots, and the runway was wet. The weather trend indicated a temporary reduction in visibility to 1500 meters with thunderstorms and showers.
Flight Sequence
The aircraft began its descent into Mumbai with no reported technical issues. During descent at approximately 7000 feet pressure altitude, the crew observed a momentary IAS disagree indication, prompting them to complete the non-normal checklist. The discrepancy did not recur. The aircraft was radar vectored for an ILS approach to Runway 27. The approach was stabilized by 3800 feet with the landing gear down, flaps set to 30, and autobrake selected to 3. The autopilot remained engaged, with the second autopilot coupled for the ILS.
At 100 feet above the runway, the pilot flying disengaged the autopilot and autothrottle. The flare maneuver consumed approximately 5807 feet of runway before touchdown, leaving 3881 feet of runway remaining. After touchdown, the speed brakes deployed automatically, and maximum reverse thrust and wheel brakes were applied. The aircraft exited the paved surface at 65 knots and came to rest 615 feet beyond the end of the runway.
Landing and Evacuation
Upon coming to rest, the flight crew instructed the cabin crew to remain at their stations. The pilots were unable to contact air traffic control via VHF radio; the pilot flying used a mobile phone to inform airline personnel of the overrun and request step ladders. Air traffic control activated fire services, and the runway was closed. The cabin crew conducted a check of the passengers. Fire services arrived and established verbal communication with the pilots through the cockpit window. Two fire personnel boarded the aircraft via the L1 door using a fire ladder. After assessing the aircraft structure and occupants, they instructed the cabin crew to evacuate using fire ladders. No injuries occurred during the evacuation or otherwise.
Probable Cause
The official investigation determined that the runway excursion resulted from a combination of factors: disconnection of the autopilot at 118 feet RA with a nose-up trim bias without adequate compensation; disconnection of the autothrottle at 118 feet RA at a higher thrust setting for that phase of flight; late touchdown of the aircraft; reduced visual cues due to heavy rain impacting depth perception and the ability to ascertain the actual touchdown position; tailwind conditions at the time of landing that increased the distance covered during the extended flare (float); and an approach with flaps set to 30 instead of the recommended 40.