Swiss Investigation of Stearman E75 (HB-RBG) Runway Excursion and Overturning at Birrfeld

Incident Overview and Aircraft Details On the afternoon of 29 June 2018, a Stearman E75 (PT-13D/N2S-5) biplane, registered as HB-RBG and owned by the Stearman Club in Altenrhein, was involved in an accident at Birrfeld Airport (LSZF). The aircraft was operating under visual flight rules for a private landing training flight. The flight crew consisted of a pilot in the rear seat and a flight instructor in the front seat. ## Flight Sequence and Accident Description The aircraft departed Birrfeld at 14:15 local time. After completing two touch-and-go landings on runway 08, the instructor demonstrated specific landing techniques. The pilot then attempted a full-stop landing. Both crew members reported that the final approach was stable in a light wind from the front left. During the flare and after touchdown, the aircraft drifted slightly to the right. The crew attempted to correct this using the rudder pedals before reaching taxi speed. The aircraft then experienced strong, symmetrical braking, as if the brakes had locked. The aircraft crossed the right edge of the runway at low speed, overturned shortly before coming to a stop, and came to rest on its back in the adjacent grass at 14:28 local time. ## Investigation Findings and Meteorological Conditions The investigation found that the toe brakes could be operated from both the front and rear seats. The instructor had conducted a training flight earlier that morning with another student and had not identified any brake defects. Following the accident, the main landing gear wheels were found to be free-spinning, and further examination of the brakes revealed no technical defects. The brake application was found to be normal and modifiable. Meteorological conditions at the time included overcast skies, dry weather, and a weak to moderate north-easterly wind. Visibility was 16 kilometers, with a wind direction of 040° at 6 knots. The temperature was 22 °C with a dew point of 15 °C, and the QNH was 1015 hPa. ## Analysis and Conclusions Both the flight instructor and the pilot had current training on tailwheel aircraft. No technical defects were found in the braking system, indicating that the loss of control was due to operational reasons. The accident, in which the biplane crossed the runway laterally after touchdown and subsequently overturned, was attributed to inappropriate use of the wheel brakes. No systemic causes were identified, and the Swiss Transportation Safety Investigation Board closed the investigation with a summary report.