David Learmount/LONDON

Just before the 17 July Alliance Air Boeing 737-200 crash on final approach to Patna, India, the aircraft underwent three pronounced, rapid roll reversals, oscillating from 47° left wing low to 34° starboard bank at impact, according to flight data recorder information just released by the Court of Inquiry. The stick-shaker stall warning system started operating 10s before the crash as the pilot was beginning a 360° orbit left, to lose excess height, and it continued until impact.

The flight had been cleared for an instrument landing system (ILS) approach to runway 25, flying the published VOR/distance measuring equipment (DME) arrival procedure to intercept the ILS. This involves approaching from the south east and turning right onto an 11nm (20km) DME arc to establish on the ILS at about 9nm. The pilot, however, did not carry out the cleared approach.

With visibility given as 4km in haze, the pilot approached from the south east, but headed direct to intercept the ILS at about 4nm DME, overshot the centreline and turned left onto a converging heading. At 2km from the runway he called for permission to carry out a 360° left orbit because the aircraft was too high - about 1,400ft (460m) above airfield level. The pilot confirmed that the aerodrome was in sight and Patna cleared him for a left orbit.

The reason for the roll reversals is not clear as the wind was calm with no reported turbulence, but the pilot had allowed the speed to decay to 119kt (171km/h) with 40° flap set. With only 7sec to impact and the stickshaker stall warning operating, the crew began the orbit, retracting the gear, but the heading altered little before the aircraft crashed 1km SE of the runway 25 threshold. All six crew and 49 of the 52 passengers died, as did five people in a building hit by the aircraft. The Court has not yet suggested a cause.

The orbit late on approach to lose height is the same manoeuvre requested by a Gulf Air Airbus A320 pilot at Bahrain on 23 August. The 737 crashed early in the attempted orbit, however, whereas the Gulf Air aircraft completed the orbit and crashed during a go-around after it (Flight International, 12-18 September).

Source: Flight International