A 1974 built de Havilland Canada DHC-6 Twin Otter 300 was operating a series of scheduled passenger flights between several islands in the Maldives, on this day in 2015. At 17:10 lt (local time) the aircraft landed at Komandoo (Maldives) where four passengers and 166 lbs of luggage were off-loaded.
The aircraft wreckage at the bottom of the sea (© AICC Maldives)
For the next sector the load sheet indicated the following payload and fuel were onboard besides the 2 pilots and cabin crew member;;
11 passengers (5 female, 4 male 2 children)
613 lb luggage
435 lb of fuel
After the necessary preparations were done, a normal take-off followed, and the crew set course for Kurudu, ~8 kilometres (5 miles) away as the crow flies. The approach to Kurudu was briefed immediately after take-off by the co-pilot, once completed the descent checklist was performed and the aircraft entered a left downwind. The co-pilot asked for 10 degrees of flap followed by a request for 20 degrees of flaps while on the base leg. The speed was reduced accordingly to 75-80 knots. On the final approach, the co-pilot asked for full flaps and moved the prop lever forward. As soon as the flaps were selected the aircraft pitched up and started to vibrate, the co-pilot stated she was no longer able to control the aircraft and transferred controls to the Pilot In Command (PIC), at that time the aircraft was in a pitch up attitude at approximately 300 feet above the sea. The PIC observed that the stall warning light had illuminated, and the aircraft was entering a spin with a low right-wing attitude.
One of the floats (Source; www.sun.mv © Uknown)
Full left rudder was applied and the control column was pushed forward while the power levers were pulled back to idle. This did not stop the nose of the aircraft to rise. The PIC then raised the flaps to the full up position, resulting in a minor controllability improvement. However, it was too late to regain control of the aircraft and it impacted the sea.
The left float detached on impact causing the aircraft to bounce followed by landing on the right float, which also detached from the aircraft, initially getting stuck between the fuselage and the engine.
After the aircraft had settled the PIC commanded an evacuation of the aircraft, and all occupants left the aircraft through the passenger door, with the PIC as the last occupant to leave the aircraft after making sure all passengers and crew had left the aircraft, Just after the PIC left the aircraft it started to sink faster and faster when it tilted left, allowing water to Irish in through the passenger door.. The wreckage settled inverted on the bottom of the sea at a depth of 36,5 meters (~120 feet). Boats from the nearby jetty and a nearby fishing vessel rescued the passengers and crew from the sea, there were no injuries. The Maldives Accident Investigation Coordinating Committee (AICC) investigated the accident and after ~18 months published their accident investigation report. The AICC identified the following causes;
The aircraft was operated outside the centre of gravity limitations on the sector in which the accident occurred.
The load distribution errors went undetected because the mass and balance calculations were not carried out in accordance with the approved procedures, prior to the accident flight.
The co-pilot (PF) was not alerted to the impending stall as she neither saw the stall warning light illuminated nor heard the aural stall warning.
The PIC was not able to gain control of the aircraft as the developing stall was not recognised and incorrect recovery procedures were applied.
In the report, safety recommendations were made to;
The Civil Aviation Authorities
The Operator
The Supplemental Type Certificate holder (STC for the floats)
Search and Rescue services
The complete AICC report is available by clicking on the .pdf file below;