Introduction
On 2 September 1972, a Bücker Lerche aircraft registered HB-URB was involved in an accident at Porrentruy aerodrome. The final report was issued by the Federal Commission of Inquiry into Aircraft Accidents on 15 December 1972.
Flight Sequence
The flight was the fourteenth and last dual-control training flight with an instructor, intended to prepare the pilot for solo release. The previous flight had been judged somewhat long, so the pilot planned a shorter approach. On final for grass runway 07, the pilot executed a sideslip to the right. As a result, the aircraft landed slightly offset to the right, touching down three-point on a mowed meadow that served as the landing area. After a roll of 35 meters, the right wheel struck the beacon marking the right front corner of the aerodrome. The landing gear was partially torn off, and the aircraft slid approximately 40 meters on its belly before coming to a stop at 1104 HEC (local time).
Damage
The pilots were uninjured. The aircraft sustained damage. No ground damage occurred.
Personnel and Aircraft Information
The pilot, born in 1946, held a valid private pilot license with a total experience of 67 hours 40 minutes, including 1 hour 14 minutes on type. In the previous 90 days, he had flown 3 hours 00 minutes, all on type. His health raised no special remarks, and the Federal Air Office records showed no prior accidents or infractions.
The instructor, born in 1933, held a valid professional pilot license with an instructor rating. His total experience was 998 hours, including 19 hours on type. In the previous 90 days, he had flown 195 hours, 11 of which on type. His health was unremarkable, and he had no record of accidents or infractions.
The aircraft Bücker Lerche HB-URB was accompanied by valid certificates of airworthiness and traffic admission.
Weather
Local meteorological conditions: cloud cover 3/8 at 4300 feet, visibility greater than 10 kilometers, wind from 060° to 070° at 8 to 12 knots, temperature +12°C, sun azimuth 152°, elevation 42°.
Analysis
The incomplete marking of the aerodrome likely made identification of the threshold of grass runway 07 more difficult. Both pilots, who had used this runway repeatedly and recently, should have been aware of this condition. The involved beacon consisted of metal drums split lengthwise and painted white. The left front corner beacon had been removed a few days earlier to allow grass mowing and had not been replaced. The pilots stated they did not see the obstacle posed by the beacon.
Causes
The accident was attributed to imprecision in maintaining the approach path and landing without certain identification of the runway threshold.