What happened
On 10 January 2021, a Morane Saullarnier - MS893 - A, registration F-BTPC, was performing a glider towing operation at La Montagne Noire aerodrome. The flight was part of a series of cable failure exercises involving a student pilot and an instructor. Following the release of the glider, the tug pilot attempted to vacate the runway area by flying over runway 21 and joining the right-hand downwind leg for runway 12.
While searching for visual contact with the glider, the aircraft entered a cloud layer, causing the pilot to lose all external visual references. Because the aircraft was not equipped for instrument flight, the pilot had no artificial horizon to maintain attitude. During the period of visual impairment, the pilot performed several 360-degree turns while climbing. The aircraft experienced two distinct losses of control; during the first, the aircraft emerged from the clouds in a high bank, and during the second, the aircraft was in a steep descent just meters above the ground.
After the second loss of control, the pilot declared a Mayday on the 121.5 MHz frequency. While flying in icing conditions and unable to maintain a steady heading, the pilot received assistance from a commercial transport pilot and a military air traffic controller. After approximately 20 minutes of flight, the aircraft broke through the cloud layer at 4,300 feet. The pilot eventually identified Revel aerodrome and landed there safely.
The investigation
The BEA examined the flight path using FLARM data, which revealed significant aerodynamic stresses. The investigation found that during the second loss of control, the aircraft's vertical speed reached a maximum nose-down rate of -9,450 ft/min, and the vertical load factor exceeded 5 g.
The investigation also reviewed meteorological data and pilot statements. It was noted that while the flight manager (the glider instructor) had observed low clouds in the morning, the instructor did not perform a formal briefing for the pilots for this specific flight program. Furthermore, the tug pilot relied on a visual assessment from an earlier flight and did not reassess the deteriorating weather conditions between the various tow flights of the day.
Findings
- The primary cause of the incident was the loss of external visual references due to the aircraft entering clouds.
- The decision to continue towing operations was influenced by a strong desire to complete flights that had been cancelled the previous day due to COVID-19 related restrictions.
- There was an error in assessing the evolution of the weather, as the pilot did not reassess the conditions at the end of each tow flight.
- The aircraft was not equipped with the necessary instrumentation, such as an artificial horizon, to maintain control in IMC.