Indian investigators believe crew fatigue contributed to a serious incident in which an Air India Airbus A319 landed on a closed Mumbai runway, without clearance and despite being instructed several times to execute a go-around.
Runway 09/27 had been temporarily closed in order for two vehicles to carry out an inspection, after a departing aircraft indicated it had sustained a bird strike.
India's aircraft accident investigation bureau says the A319 (VT-SCL), arriving from Abu Dhabi, had been 8-10nm from Mumbai when it was instructed by approach control to contact Mumbai tower.
"After this there was no response or contact made by the aircraft," says the inquiry. The tower made "several" go-around calls to the aircraft, it adds, "but there was no reply".
One of the vehicle's crews observed an aircraft on short final for runway 27 and instructed the other vehicle to vacate immediately. Both left the runway before the jet touched down.
The captain, as the monitoring pilot, had been trying to establish contact on the tower frequency at the time but was unsuccessful.
"At the time there was a lot of disturbance and garbling on the frequency," says the inquiry.
It adds that, at around 900ft, the pilots saw two vehicles near taxiway N5 and decided that, should they not clear the runway, the A319 would abort its approach at the decision height of 230ft. The vehicles vacated the runway by the time the jet descended through 500ft.
Despite the crew's advising that a communication failure had led to the landing without clearance, the aircraft was not checked for any communication problem before being cleared to operate the next sector and the cockpit-voice recorder was not removed.
None of the 88 occupants was injured in the 12 April 2013 incident and the aircraft was undamaged.
Investigators state that the crew did not communicate with air traffic control on any tower frequency. It adds that fatigue "contributed to the error", and has recommended that processes be implemented to report and evaluate fatigue-related events.