Factual Information
On 29 August 2017, at approximately 13:14 local time, a Robin DR 400/180 aircraft, registered as HB-KFY, collided with an earth wall after landing on runway 28 at Raron Airfield (LSTA) in the municipality of Raron, Valais, Switzerland. The flight was a private visual flight rules (VFR) alpine sightseeing flight with a pilot and one passenger. The pilot, a Swiss national born in 1948, held a Private Pilot License (PPL(A)) issued by the European Aviation Safety Agency (EASA) via the Swiss Federal Office of Civil Aviation (BAZL). He had a total of 635 flight hours, with 601 hours on the accident aircraft type. In the 90 days prior to the accident, he had flown 12 hours total, all on the accident type. The aircraft was owned and operated by the Fluggruppe Oberwallis.
Sequence of Events
The pilot planned a two-hour alpine round flight in the Upper Valais region. In the week before the accident, he had performed similar flights with seven landings on runway 28 at Raron. On the day of the accident, the aircraft taxied to runway 28 at about 11:00 hours. During taxi, the pilot heard a rattling noise, which stopped after a brake test. The aircraft departed at 11:15 hours and returned after an uneventful flight at 13:14 hours.
The pilot selected a direct approach from the east for runway 28, broadcasting the intention on the airfield frequency. The approach followed a visual approach chart published by the Fluggruppe Oberwallis. According to the pilot, the aircraft touched down normally. A witness, located about 50 meters before the runway end, saw the aircraft on final approach and observed nothing unusual. He did not see the touchdown but heard tire squealing and saw the aircraft collide with an earth wall behind the runway end, where it came to a stop. The witness reported that braking appeared to have been initiated very late. The pilot stated that a go-around was considered too risky due to buildings in the runway extension.
The occupants were not injured in the impact. No fire occurred. Several vehicles parked behind the earth wall were damaged by flying debris. The emergency locator transmitter was not activated. The pilot reported that the braking system had not functioned correctly, prompting an investigation.
Aircraft Information
The Robin DR 400/180 is a single-engine, four-seat, low-wing aircraft with a fixed tricycle landing gear, wooden construction, and fabric covering. The aircraft had a total of 3539 operating hours at the time of the accident. The last 50-hour check was certified on 3 August 2017 at 3529 hours. A 500-hour check had been completed on 26 April 2017 at 3483 hours. No technical restrictions were recorded in the flight logbook.
The braking system consists of hydraulic disc brakes with separate oil-hydraulic systems for each main wheel, operated by left and right brake pedals. The parking brake system includes a valve that can be operated by a small lever. The airspeed indicator (ASI) had been removed and repaired on 11 November 2016. Following reinstallation, the system was tested and found satisfactory. Multiple pilot-reported anomalies with the ASI were recorded in the flight logbook until 20 May 2017. On 24 May 2017, a note in the logbook referenced work report 37005 stating "airspeed controls in order." According to work report 37005 of 27 July 2017, the ASI was removed for testing by an external company, reinstalled, and the pitot tube was replaced. The system was tested with a pitot-static tester and found satisfactory.
The take-off mass was approximately 910 kg and the landing mass approximately 845 kg, both within limits. According to the Aircraft Flight Manual (AFM), the landing distance at the prevailing density altitude was about 240 m, based on a touchdown speed of 51 kt. The recommended approach speed at maximum landing mass was 68 kt.
Investigation Findings
A detailed examination of the braking system was conducted. Minor irregularities were found, such as low tire pressure and slight tire-to-rim movement. Brake pads were 50% worn, and discs showed normal wear. These findings were assessed as having no effect on braking performance, and the braking system was considered to have functioned correctly.
The airspeed indicator system was tested with a calibrated pitot-static test set. The pitot tube, deformed and filled with soil from the impact, was removed for testing; the test line was connected directly to the pitot line at the wing leading edge. The system was found to be leak-free, and both airspeed and altitude indications were accurate across various speed and altitude ranges.
The brakes and airspeed indicator were therefore not determined to be factors in the accident.
The accident site showed visible brake marks beginning approximately 192 m from the earth wall, slightly offset to the right of the runway centerline, with almost no interruptions.