Alliance Air Flight 7412

Flight 7412 departed Calcutta (Kolkata) at 06:51 on 17 July 2000, for a flight to Delhi, with stops at Patna and Lucknow. Patna ATC asked the aircraft at 07:17 to report for descent and also to check descent traffic with Kolkata Area Control. The aircraft soon responded that Kolkata had reported negative traffic. Flight 7412 was then cleared for descent to FL75 and asked to report 25 NM and the same was reported by the aircraft at 07:26. Flight 7412 was cleared to descend to 4000 ft. and was asked to report for approach runway 25.[1]

At 07:28, Flight 7412 reported commencing the turn and at 07:31 reported crossing the airport area and coming up on the localiser. Flight 7412 was then asked to descend to 1700 ft. The crew had been cleared to land at runway 25 at Lok Nayak Jayaprakash Airport at Patna when the pilots requested a 360-degree orbit due to the flight being high on the approach. Permission was granted and a left turn was initiated. During the left turn, the aircraft stalled. The plane then grazed a few single-storied houses in a government residential housing estate and crashed in a government residential colony behind Gardani Bagh Girls School at Anishabad, which is located about 2 km southwest of the Patna Airport.[3] The aircraft broke into four pieces.[3]

When the aircraft struck the residential quarters and the ground, the impact was severe. The intensity of post impact fire was also severe. Initially, seven passengers were extricated alive. Of them, six were seriously injured. Miraculously, one of the passengers walked out of the wreckage without much injury even though he had a minor concussion and was treated later. Of the six injured passengers, four died subsequently. Two passengers recovered completely after treatment.[1]

The airport ambulance had proceeded to the crash site along with the CFTs. Two injured passengers were transported to the PMCH in the first instance. Subsequently, the second ambulance from the airport was also pressed into service to transport the remaining injured passengers for medical aid. Shortly after the arrival of the airport ambulance, ambulances from other assisting agencies also arrived and helped in removing all the injured for medical aid.[1]

The aircraft involved in the accident was a Boeing 737-200. Boeing 737-200 is a twin-engine jet transport airplane manufactured by Boeing Commercial Airplane Company, USA. It is designed to operate over short to medium ranges at cruise speeds of approximately 950 kilometres per hour (km/h). Two P&W JT8D/17A engines power the aircraft, each developing approximately 16,000 pounds (lbf) of thrust at sea level.[1]

The aircraft involved in the accident was registered in India as VT-EGD with a serial number of MSN22280. The aircraft was manufactured in 1980 and sold to Indian Airlines. It was subsequently leased to Alliance Air in 1999.[1]

The aircraft in question, VT-EGD, had been involved in an earlier accident. On 15 January 1986, the pilot of flight 529 attempted to land at Tiruchirapalli in conditions below weather minima (reported Wx was exactly the minima). During a go-around (wave-off, just before touch down) the wing contacted the runway due to an excessive bank angle (the delay in spool-up times for both engines were more than 5 seconds apart with the right engine slow). The HIALS was not switched on at the time 529 was approaching and the ATC anemometer was unserviceable. The wing was substantially damaged, but there were no injuries among the 6 crew and 122 passengers. The pilot displayed great skill in manually flying the B737 at FL100 and diverted to Chennai and landed safely with flight controls in "manual reversion" on runway 07[3][5] The aircraft was to be phased out by the end of the year per Indian government guidelines which do not allow aircraft over 20 years old to operate in Indian airspace.[6]

Investigators ruled out terrorism as the cause of the accident. They didn't find any signs of explosion nor a fire had occurred in flight. Both pilots were not intoxicated and fully aware at the time of the crash.[1]

The flight crew consisted of Captain Manjit Singh Sohanpal and co-pilot Arvind Singh Bagga. A criminal case, filed against them based on the statement of a surviving passenger, was later withdrawn.[6][7] Both Captain Sohanpal and co-pilot Bagga died in the accident.[6]

A TAESA Boeing 737 with the rudder (yellow) visible.

Investigators later conducted an observation with its Rudder Power Control Unit (PCU). The Main Power Control Unit (MPCU) of the rudder has been a subject of intense debate and discussions and has undergone mandatory modifications as a result of some previous accident investigations. The PCU has responsible for several high-profile crashes, such as United Airlines Flight 585, USAir Flight 427, and Eastwind Airlines Flight 517. Flight 7412 nose-dived before the crash, as well as two previous crashes, Flight 585 and Flight 427. The rudder locked up in a particular direction, and reversal of rudder to that of the commanded position (anomalous rudder movements such as un-commanded movements). These have been attributed to the secondary slide jamming with the primary slide due to contamination or adverse buildup of tolerances during manufacture. However, investigators later dismissed it and ruled out the failure of the PCU as the cause, and concluded that it was serviceable and was in good condition.[1]

As both black boxes were found by search and rescue teams, investigators tore into both black boxes and analyzed their contents. The results showed that the engines were at idle thrust throughout the descent profile and the speed was continuously reducing. It was not clear why the engines were kept at idle thrust even after selecting Flaps 40. It was perhaps because the aircraft was higher than normal on approach. If the intention was to regain the correct glide path then classic flying technique would have required the Pilot to maintain speed by reducing the angle of attack by pushing the control column forward while allowing the aircraft to regain the correct glide path with an increased rate of descent.[1]

When it was realized that the aircraft was too high to effect a landing, a 360° orbit was requested. The landing reference speed or threshold crossing speed at this time was 119 knots, the landing speed. The procedure to carry out a 360° turn was not an authorised procedure as per the Alliance Air Operations Manual and could have caused confusion in the mind of First Officer Arvind. It was clear from the FDR recording that the aircraft was not following the ILS procedure but Patna ATC was being given the impression that the aircraft was doing so.

At any busy airport, this would have been unthinkable and would have created a conflict. However, there was no other traffic for miles around Patna and ATC gave the permission after confirming that the crew had the airfield in sight. Captain Manjit tried to resolve this issue without any discussion with First Officer Arvind. The atmosphere in the cockpit was relaxed and tension free till 15 seconds before the crash. The first sign of anxiety became apparent only when Arvind called for raising the landing gear.[1]

Investigators conducted a simulation of the crash and found that at 16 seconds before the crash, the spooling up of the engine had reduced the rate of descent. However, eight seconds later when the Flap Lever was moved to 15, the rate of descent increased as seen by the steepening of the slope of the curve. This was caused by loss of lift due to the reduction in wing area as the flaps moved up from 40 to 15. Six seconds after the flap Lever was moved to 15, the rate of descent increased even further indicating that the flaps were close to 15 position and the wing no longer generated enough lift to support the aircraft. This high rate of descent together with the high Nose Up pitch attitude held by the pilot resulted in the aircraft attaining a very high angle of attack of the order of 26^o. 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.[1]

The final investigation noted pilot error as the cause of the plane crash.[8] According to the panel, the crew had not followed the correct approach procedure, which resulted in the aircraft being high on approach. The engines had been kept at idle thrust, which allowed the airspeed to decline below the allowed minimum for approach and caused the aircraft to stall. The inquiry also pointed out that the airport had "several operational constraints, resulting in erosion of safety margins for the operation of Airbus 320s and Boeing 737s."

There were a number of aspersions cast on the maintenance of flights by Alliance Air, with the then civil aviation minister Sharad Yadav reportedly unhappy with the maintenance of the aircraft[9] and asking for replacement of a number of additional aircraft.[9] Some reports even claimed that one of the engines was on fire before the crash.[6] However, the investigation clearly said the aircraft was fully airworthy and was properly maintained.[6]

• Air India Express Flight 812
• List of accidents and incidents involving commercial aircraft
• Vidya Malvade (Indian film actress), wife of Capt. Arvind Singh Bagga

• Accident description at the Aviation Safety Network
• Final Accident Report - REPORT ON ACCIDENT TO ALLIANCE AIR BOEING 737-200 AIRCRAFT VT-EGD ON 17TH JULY, 2000 AT PATNA BY THE COURT OF INQUIRY AIR MARSHAL P. RAJ KUMAR, PVSM, AVSM, VM PROGRAMME DIRECTOR (FLIGHT TEST) AERONAUTICAL DEVELOPMENT AGENCY, BANGLORE - Posted on the website of the India Ministry of Civil Aviation (Archive in text format, archive in PDF format)
• Cockpit Voice Recorder transcript and accident summary
• Wg Cdr G Gomez. "Case Report: Human factor analysis of Alliance air crash flight CD-7412" (Archive). Indian Journal of Aerospace Medicine (Ind J Aerospace Med) 46(1), 2002. p. 66-74.