SpiceJet flight SG6237, a Boeing 737-800, suffered a runway excursion after landing on runway 27 at Mumbai, India in moderate to heavy rain. The flight departed Jaipur International Airport with the captain as Pilot Flying. The pilots had carried out briefing for the approach including the weather and go around actions, if required. The aircraft commenced descent into Mumbai in the late evening hours. As per the reported weather at the time of approach visibility was 2100 metres in rain. Reported winds were 090/12 Knots. Runway was wet and the trend provided was “temporary reduction in visibility to 1500 metres with thunder/ showers of rain”. During descend at an IAS disagree warning was observed, indicating a discrepancy of airspeed between the instrument sources for the flight crew. Although this indication was momentary, the Non-Normal Checklist was carried out. The indication discrepancy did not recur for the remainder of the flight. The aircraft was radar vectored for an ILS approach for Runway 27 at Mumbai. The approach was stabilized by 38700 feet with landing gear down and flaps 30 and auto brake selected at 3. The autopilot was engaged throughout the descent phase and during approach, the second autopilot was coupled for the ILS approach. At 100 feet, the autopilot and the auto-throttle were disengaged by the PF. The flare manoeuvre consumed approximately 5807 feet of the runway length prior to touchdown with 3881 feet 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 at a distance of 615 feet beyond the end of the runway. The nose landing gear had collapsed. Once the aircraft came to rest, the flight crew advised cabin crew to be at their stations. The pilots were unable to contact ATC through VHF communication. The PF contacted his airline personnel using mobile phone and informed that the aircraft had overrun the runway and requested for step ladders. The ATC activated fire services and the runway was closed for operation. An assessment of the aircraft structure and occupants was made and the fire services personnel informed the cabin crew that deplaning was to be carried out using fire ladders. There were no injuries during evacuation or otherwise. Probable Cause The runway excursion occurred because of combination of: – Disconnection of auto pilot at an altitude 118′ RA with the nose up trim bias without adequate compensation. – Disconnection of auto throttle at 118′ RA at a higher thrust setting for that phase of flight. – Late touchdown of the aircraft on the runway. – Reduced visual cues due to heavy rain impacting depth perception and ascertaining of actual touchdown position. – Tailwind conditions at the time of landing resulting In increasing the distance covered during the extended flare (float). – Approach with lower flaps (30) than recommended (40).