The aircraft, which was operating the Tokyo-London passenger service Speedbird 931 of BOAC, was attempting to land at Calcutta Airport with the aid of the Instrument Landing System. The earlier stages of the approach to Runway 19L proceeded without incident. Turbulence was encountered necessitating increased power to stabilize the fluctuating air speed at the recommended figure. The increased power was applied too late with the result that sudden sinking of the aircraft and an impact with trees could not be avoided. Thereafter, partial loss of lateral control was experienced as considerable damage had been caused to the flaps. The missed approach procedure was then successfully carried out. The next approach was made on to runway 01R. The aircraft was then being flown by visual reference. During this approach the aircraft again impacted the trees as due allowance was not made for the higher stalling speed of the damaged aircraft. Missed approach procedure was again initiated and the aircraft responded well. However, further damage had been sustained. A circuit was executed and the landing during the third attempt was successful, but the damaged aircraft failed to pull up within the available length of the wet runway because of the higher speed at which the approach had to be justifiably made. No injury was sustained by the 44 passengers and nine members of the crew on board. The aircraft was substantially damaged. Accident causes: The accident is attributed to an error of judgement on the part of flying crew in not applying power when approaching to land under turbulent conditions. The subsequent power increase was applied too late to prevent the aircraft, which was being flown at a speed below the speed recommended for turbulent conditions, from sinking and striking trees.