Background
Pakistan International Airlines Flight 17 was a scheduled domestic passenger service from Dacca to Faridpur in East Pakistan. The aircraft involved was a Sikorsky S-61N registered as AP-AOC, which was airworthy for the flight. Onboard were 21 passengers and 3 crew members. The crew consisted of 34-year-old Captain Shamsul Alam, 30-year-old First Officer Nurur Rahman, and 22-year-old flight attendant Ayub. Both pilots were properly trained and certificated.
Accident
On 2 February 1966, the helicopter departed Dacca at 14:03 local time. Within 15 minutes, an oil leak began from an external pipe connected to the main gearbox. At 14:18:32, the crew reported leaving the Dacca control zone, and at 14:19 they contacted Faridpur Heliport, stating they were 25 nautical miles out at 500 feet. While crossing the Padma River, the sole survivor noticed oil visible in the passenger cabin. About 3 miles from Faridpur, a vulture struck one of the retreating rotor blades, but the flight continued normally. On final approach, at an altitude of 300 feet and speed not exceeding 90 knots with landing gear extended, the helicopter experienced a loss of power to the main transmission despite both engines running normally. The pilot corrected an initial left turn, but then the helicopter turned 90 degrees and entered a steep, uncontrolled descent with rolling and rocking. At 14:23, it crashed nose-low with a 30-degree right bank. Witnesses reported seeing white smoke under the rotor head. A fire broke out. Passenger Muhammad Abdul Mannan escaped and was taken to Faridpur Hospital without injuries. The remaining 23 occupants died in the fire.
Aftermath
Rescue efforts were hampered by inadequate equipment and difficult terrain. Despite every effort, the response was considered unsatisfactory. On the same day, Asghar Khan, the Chief Administrator of Civil Aviation, ordered an investigation, and a team from Civil Aviation and PIA departed for Dacca.
Investigation
The investigation determined that the aircraft was intact at impact with main rotors operating. The bird strike had negligible effect, with no evidence of in-flight breakup or subsequent abnormalities. The accident was attributed to disengagement of the left and right spur gear teeth in the main transmission, caused by the load imposed by failure of the gearbox's rear sleeve bearing journals. That bearing failure was caused by an oil leak, though evidence was destroyed.