What happened
On September 3, 2011, a Rans S6 Coyote II ultralight aircraft departed from Tannheim airfield for a visual flight toward Landshut. Around 12:00 PM, witnesses observed the aircraft flying low over the town of Sinningen and performing maneuvers over a nearby recreational lake. During one of these passes, onlookers noted the aircraft exhibiting a rolling motion (wing rocking) before the pilot executed a steep climb. Following this ascent, the aircraft stalled over its right wing and plummeted nearly vertically into the lake.
At the time of the accident, a rescue diver training exercise was underway in the same lake. Divers recovered the two occupants from the cockpit at a depth of approximately 5 meters. Although both individuals were initially resuscitated, the passenger subsequently died from their injuries. The pilot sustained serious injuries.
The investigation
The BFU investigation focused on the aircraft's weight, balance, and recent modifications. While the pilot held valid licenses and sufficient experience for the aircraft type, the investigation revealed that the aircraft had undergone several undocumented modifications by the owner. These included the installation of an adjustable Alisport-Idrovario propeller, a transponder, an autoradio, and an additional 11-US-gallon auxiliary fuel tank located behind the pilot's seat.
Investigators examined the aircraft's mass and center of gravity. The investigation established that the aircraft was significantly overloaded. The combined weight of the pilot, passenger, luggage, and equipment, when added to the empty weight, exceeded the maximum takeoff mass (MTOM). Furthermore, the installation of the auxiliary tank and other components shifted the center of gravity significantly toward the rear, outside of the permitted limits.
Findings
- The aircraft was overloaded, exceeding its maximum takeoff mass.
- The center of gravity was located too far aft due to the installation of an unauthorized auxiliary fuel tank and other equipment.
- Unapproved modifications, including the installation of a variable-pitch propeller and a non-compliant fuel system, altered the aircraft's handling characteristics, particularly in flight regimes near the edges of the envelope.
- The accident was caused by the pilot flying at a low altitude with a high angle of attack, which led to a loss of airspeed and a subsequent spin that could not be recovered due to the low altitude.
Safety action
- The BFU issued safety recommendation 20/2012 to the German Aero Club (DAeC), requesting that they inspect the Rans S6 fleet to ensure that all fuel systems comply with the original type certification.