Investigation Summary
The approach to Saint Barthélemy's Runway 10 is notoriously difficult, requiring a steep descent over the Col de la Tourmente ridge followed by a rapid flare to land on a short runway. On the day of the accident, the captain, who had significant experience on the Twin Otter but had recently lacked time on the type, was under time pressure. To manage the steep descent, he utilized the 'beta' range of the propellers, a setting intended for ground operations that allows for reverse thrust or zero thrust by flattening the blade pitch. While not authorized for use in flight, some pilots used it as an improvised speed brake. Analysis of a passenger's recovered video camera provided critical acoustic evidence of propeller desynchronization. As the pilot attempted to transition back to forward thrust, the engines did not respond symmetrically. The resulting massive yawing moment caused the aircraft to bank steeply to the left and dive into a residential area. While the captain was the likely pilot flying, the BEA could not entirely rule out a second hypothesis where the less-experienced First Officer was flying the approach under the captain's supervision, which would have made thrust lever manipulation more difficult from the right seat.
Final Conclusions
The BEA concluded the accident resulted from the captain's use of the propellers in the reverse beta range to improve track control on short final. The resulting thrust asymmetry caused a loss of control. Contributory factors included the captain's lack of recent experience on the DHC-6, the inherent difficulty of the approach to Runway 10, and time pressure. The low height of the upset was cited as an aggravating factor that made recovery impossible.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Jean-Paul Jerpan, age 38.
First Officer
Nicolas Manen, age 38. Previously a flight engineer in the French Air Force.
Systems & Failure Modes
Beta Range
A propeller pitch regime where the blade angle is controlled directly by the power lever rather than a governor. It is intended for ground maneuvering and reverse thrust, but its unauthorized use in flight can cause catastrophic drag or thrust asymmetry.
Hartzell Propellers
The aircraft was equipped with three-bladed constant-speed propellers. Post-crash inspection showed the left propeller was at a pitch of 20.4 degrees, indicating it was above flight idle at impact.
Interesting Facts
- 01The aircraft was not equipped with a Cockpit Voice Recorder (CVR) or Flight Data Recorder (FDR) due to regulatory waivers for older aircraft.
- 02Investigators relied on a recovered passenger video camera to analyze engine sounds and propeller synchronization.
- 03The crash killed 17 passengers, 2 crew members, and 1 person on the ground.
- 04The captain had 9,864 total flying hours, with 5,000 hours on the Twin Otter type.
- 05The first officer had only 15 hours of experience on the DHC-6 Twin Otter.
Safety Actions & Advisories
Flight Recorder Mandates
The BEA recommended that the DGAC and JAA remove waivers and require at least one flight recorder on all public transport aircraft authorized to carry more than nine passengers, regardless of age or weight.