Alliance Air Flight 7412

Alliance Air Flight 7412 was a scheduled Indian domestic passenger flight from Calcutta to Delhi, operated by Indian regional airline Alliance Air. On 17 July 2000, while on approach to its first stopover in Patna, the Boeing 737-200 operating the route nose-dived and crashed into a residential area in Patna, killing 60 people including 5 on the ground.

The final report, investigated by the Indian Directorate General of Civil Aviation, concluded that the cause of the crash was due to pilot error. The aircraft was on approach with its engines at idle thrust and the crew made several maneuvers with high-pitch attitude. When the aircraft sounded a warning on an impending stall, the crew elected to execute a go-around procedure instead of a stall recovery procedure, causing the aircraft to enter an actual stall condition.

Accident

Flight 7412 departed Calcutta (now Kolkata) at 06:51 local time on 17 July 2000 for a flight to the Indian capital of Delhi, with stops at Patna and Lucknow, carrying 52 passengers and 6 crew members. The aircraft was flown by Captain Bagga with Captain Sohanpal as his co-pilot. The flight was uneventful until its approach.

At 07:12 a.m, the aircraft was handed over to Patna following its take-off from Calcutta. At 07:17 a.m, during the approach, Patna ATC asked the crew to report for descent and also to check descent traffic with Calcutta Area Control. The aircraft was then cleared for descent to flight level 75 (approximately 7500 ft) and eventually to 4000 ft. Flight crews were asked to report for an approach to runway 25.

The flight crew reported commencing the turn to Patna at 07:28 a.m and three minutes later they reported crossing the airport area and coming up on the localiser. The aircraft was then asked to descend to 1700 ft. Patna ATC later cleared the aircraft to land at Runway 25. The flight crew, however, noticed that their altitude was much higher than the usual altitude for an approach and requested the ATC for a 360-degree orbit. The ATC granted their request and asked the crew to report back on the approach, which the crew acknowledged. This was the last transmission from the crew.

Following the aircraft's clearance for a circle, the flight crew attempted a turn to the left. At the time, the aircraft was flying above Patna's Secretariat Tower. During the left turn, the stick shaker activated, warning the crew on the impending stall condition. The aircraft continued to bank, losing its altitude and eventually grazed trees and a single-storied house in a government residential housing estate, crashing in a government residential colony behind Gardani Bagh Girls School at 07:34 a.m.

Plumes of smoke immediately appeared from the last area where the aircraft was last seen. Patna ATC immediately activated the crash alarm and reported the crash of Flight 7412 to fire services. Authorities arrived at the crash site approximately 15 to 20 minutes after the accident. The accident sparked fire in the area due to the aircraft's 2,5 tonnes of fuel. The search and rescue operation was hampered by the narrow roads and large volumes of people. Airport officials and police were met with anger from locals due to the chaotic situation. Dozens of onlookers even tried to climb rescue vehicles to get a better view on the crash site. The situation finally came under some control after multiple jawans and military officers were deployed to the area.

Two houses were destroyed while another house had damages on the roof. A total of seven people were found alive from the site, four of whom later succumbed due to their injuries. One passenger, a male teenager, managed to survive unscathed from the crash and was able to walk away from the wreckage. Those who survived the crash were seated at the aft fuselage. A total of 60 people, including 5 people on the ground, were killed in the crash.

Flight recorders analysis

The flight recorders indicated that Captain Bagga was on the left seat and Captain Sohanpal was on the right seat. Captain Bagga was the one in control while Captain Sohanpal was the one in charge with the radio communication. According to the recordings, the sequence of events were as follow:

Flight 7412 had followed the established approach procedure up until 07:28 a.m when Patna ATC asked the flight crew to start turning to the direction of the airport. The flight crew acknowledged the message. However, the aircraft didn't turn. They should have started their descent to 2,000 ft while commencing the turn but the aircraft remained at the same altitude and heading, even though two minutes had passed since the message was sent from the ATC. The controller in Patna was given the impression that the flight crew was following the standard approach procedure to Patna, while in reality there was no intention to commence the turn. Captain Sohanpal should have briefed Captain Bagga about the matter, however the recording didn't capture any response from Captain Sohanpal.

The aircraft then started to bank multiple times. It first banked to the left, and then to the right, and to the left again. All of this took 3 and a half minutes with different flaps configurations; 1 degree, 5 degree and 15 degree, respectively. The crew tried to make a zig zag motion in order to lengthen their approach path, thus gradually decreasing their altitude. The aircraft had just crossed the lead radial at an altitude of 3,000 ft and was just 3.5 nmi from the distance measuring equipment (DME). The correct procedure stated that an aircraft should have been at an altitude of 2,000 ft and was 11 nmi from the DME while it was crossing the lead radial. If they were higher than said altitude and was at a closer distance than the normal flight profile then they would be at an altitude that was too high for an approach to the airport.

The aircraft crossed the extended runway centre line and entered a zig-zag motion again, first to the left and then to the right. The flaps changed from 15 degree to 40 degree. During the entire sequence, from the start of the zig-zag until 15 seconds before the crash, the engines remained at idle position. The reason why the engines were set at idle was not clear, though investigators suspected that it was due to their high altitude for an approach.

At 07:32 a.m, the aircraft reached Patna. It was at 1.2 nmi from the DME. As per the approach chart, the aircraft should have been at an altitude of 610 to 650 ft while it was at a distance of 1.2 nmi. The aircraft, however, was at an altitude of 1,280 ft. By this point, the crew should have discussed on the next course of action. Captain Sohanpal, however, didn't discuss his next action to Captain Bagga and instead immediately decided to request a 360 degree orbit to Patna ATC, which was granted. This was not in accordance with the Standard Operating Manual (SOP) of Alliance Air and would have probably caused confusion with Captain Bagga due to the unusual decision from Captain Sohanpal. Alliance Air approach manual stated that the crew should have initiated a missed approach procedure. The airspeed, at the time, was still at 130 knots.

Following the aircraft's clearance to orbit, the flight crew initiated a steep left turn and then a right turn. The flight crew made a zig zag motion again, with 21 degree to the left, 14 degree to the right, 47 degree to the left and 30 degree to the right. The pitch was changed from nose down to 8 degree nose up, before it eventually reached 16 degree nose up. The airspeed then dropped from 130 to 122 kn. It eventually dropped to 119 kn. Both pilots didn't realize that the speed had dropped. Captain Bagga was looking out the runway while Captain Sohanpal was busy with conversation. The low speed of the aircraft caused the activation of the stick shaker, warning the crew on the impending stall condition.

Within 2 seconds, the engine thrust was increased and the aircraft started to climb. The landing gear was retracted. The crew then decided to switch the flap angle from 40 degree to 15 degree. This was the correct procedure for a go-around, not a stall recovery. When confronted by a stall, the crew should have applied full engine thrust and reduced the aircraft's nose pitch. They also shouldn't have changed the aircraft's flap configuration. The switching of the flap to 15 degree caused a substantial loss of lift due to the reduction of downwards airflow. Six seconds later, the aircraft attained a high rate of descent. The wings no longer generated enough lift. The nose angle remained in up position. The aircraft had completely stalled by this time and even though thrust had been increased to the maximum possible on both engines, recovery was not possible.