Introduction
The Slovenian Ministry of Infrastructure, Service for Investigation of Aviation, Maritime and Railway Accidents and Incidents, has published its final report on the accident of a Pierre Robin DR400/180, registration D-EFTW, which occurred near Bovec airfield (LJBO) on 29 July 2018.
Factual Information
The accident happened while the aircraft was performing an aerotow of a glider. The aircraft was completely destroyed. The pilot was the sole occupant. The fuel selector valve was found in the OFF position. The tow rope had separated; subsequent analysis of the rope was conducted by the Slovenian National Building and Civil Engineering Institute (ZAG). The propeller sustained damage consistent with a non-powered impact. Meteorological data from the airfield were recorded, including wind, temperature, and pressure.
Analysis
The investigation examined the tow rope failure, the fuel selector position, fuel usage, and propeller damage. The tow rope was found to have a reduced breaking strength due to abrasion at the point of failure. The fuel selector valve was in the OFF position, but engine operation at impact was inferred from propeller damage patterns. The pilot's handling during the aerotow was assessed; the aircraft entered a stall/spin from which recovery was not possible. The fuel quantity indicators and the emergency electric fuel pump were also evaluated.
Conclusions
The investigation determined that the direct cause of the accident was the pilot's improper handling of the aircraft during the aerotow, leading to an unrecoverable stall/spin. Indirect causes included factors such as the fuel selector position and the condition of the tow rope, but these were not cited as primary causes.
Probable Cause
The pilot, while performing aerotow of a glider with the DR 400/180, D-EFTW, due to improper handling of the aircraft, entered a stall/spin situation from which he could not recover.