What happened
On 11 July 2011, a De Havillable DHC-6-300 Twin Otter, registration 8Q-TMD, was conducting a routine annual recurrent training flight in the Maldives. The flight, operated by Trans Maldivian Airways, involved several maneuvers including stalls, steep turns, and rejected takeoffs over a training lagoon.
During the final maneuver of the session, the crew attempted to simulate a single-engine landing with a tailwind. For this exercise, power was reduced on the right engine. The crew chose to land in the deep water of a channel outside the lagoon. While the initial touchdown appeared smooth, the aircraft struck a high wave, causing the plane to bounce approximately 20 feet into the air.
At a low airspeed, the aircraft banked sharply. The left float struck the water with significant force, causing the structural attachments to the fuselage to fail. The impact caused the aircraft to pivot and bounce again, damaging the right-side struts. The resulting movement caused the floats to twist upward, striking the bottom engine cowlings and causing the propellers to strike the floats. The aircraft eventually came to rest on a reef, partially submerged.
The investigation
The AICC investigation examined the wreckage, interviewed the two crew members, and conducted metallurgical testing on broken components. The investigation confirmed that both pilots were qualified, experienced, and medically fit, with no evidence of impairment from drugs or alcohol.
Metallurgical analysis of the spreader bars and float attachments showed no signs of fatigue or pre-existing cracks; instead, the fractures indicated an overload failure, meaning the physical forces during the landing exceeded the material strength. The investigation also noted that the aircraft was within weight limits and that the aircraft's maintenance was up to date.
Findings
- The primary cause of the accident was the impact with a high swell during landing, which led to a high bounce and a subsequent hard landing that detached the float attachments.
- A major contributing factor was an abnormal landing configuration, specifically the use of zero flaps during a single-engine landing simulation, which resulted in a higher than normal touchdown speed.
- The crew selected an inappropriate landing site and direction (tail wind) based on the prevailing surface conditions.
- The simulation of multiple emergencies simultaneously increased complexity.
- Time pressure existed as the crew needed to return to base to perform scheduled commercial flights.
Safety action
- The operator should review standard operating procedures (SOPs) regarding single-engine operations and emergency maneuvers.
- Flight training for instructors should include Full Flight Simulator (FFS) training for all Type Rating Instructors and Examiners.
- The Civil Aviation Department should formally designate specific flight training areas.
- Procedures should ensure adequate time is allocated for debriefing between training and commercial flight duties.
- Training programs should avoid the simultaneous simulation of multiple emergencies.