What happened
On August 1, 2014, a Saab 91B operated by a German commercial operator departed from Bremen Airport on runway 09 for a visual flight rules (VFR) flight. The aircraft was carrying a pilot and one passenger. Shortly after takeoff, the pilot contacted the tower to declare an immediate need to land.
During the initial climb, the aircraft was in a clean configuration at approximately 300 ft AMSL. While executing a left-hand turn, the aircraft's nose pitched down, and the pilot applied right aileron and back pressure on the elevator. The aircraft entered a left-hand stall and impacted the ground approximately 0.5 nautical miles northeast of the threshold of runway 27. The impact caused the aircraft to strike a freight container, and a subsequent fire destroyed the fuselage, left wing, and tail section. The two fatalities on board were caused by polytrauma sustained during the impact.
The investigation
The BFU examined the aircraft wreckage, engine components, and radar data. The investigation included a review of the pilot's extensive flight experience and the operator's safety management systems. Investigators also analyzed photographic evidence of the aircraft's flight path and examined the engine for any signs of mechanical failure. The investigation also looked into the possibility of an unsecured oil filler cap, as the cap was found dislodged near the engine cylinders.
Findings
- The primary cause of the accident was that the pilot failed to maintain the required airspeed during a left-hand turn, leading the aircraft into an aerodynamic stall.
- The pilot's attention may have been distracted by oil vapors or oil spray hitting the cockpit windscreen, likely caused by an unsecured oil filler cap that had been left open after a pre-flight check.
- The aircraft's airspeed was only slightly above the stall speed for a 30-degree bank angle, and the onset of a vertical gust may have further reduced the margin.
- The pilot's training regarding stall recovery and handling of extreme flight envelopes specifically for the Saab 91B was insufficient.
- The operator's safety management system failed to ensure that the pilot underwent specific proficiency checks for handling such flight conditions on this aircraft type.