What happened
On February 3, 2023, at approximately 16:20 local time, a LET L-33 SOLO glider was performing a local flight pattern near the Vitacura Municipal Aerodrome (SCLC) in Chile. After a 50-minute flight, the pilot began the standard approach for landing on runway 26. During the crosswind leg of the traffic pattern, the pilot realized the aircraft was at an altitude too low to safely complete the planned landing on the runway. To avoid obstacles and maintain safety, the pilot opted to execute an emergency landing in the Mapocho Riverbed, located roughly 750 meters east of the runway threshold.
Upon contact with the uneven terrain of the riverbed, the aircraft's right wing struck an obstacle, causing the glider to swerve and come to a stop. The impact resulted in serious injuries to the pilot and significant structural damage to the aircraft, particularly to the nose section.
The investigation
DGAC Chile examined the flight logs, maintenance records, and the physical wreckage of the glider. The investigation confirmed that the pilot held a valid glider license and had met all recent flight experience requirements. Maintenance records showed the aircraft had undergone its annual inspection earlier that year and was in an airworthy condition.
Investigators analyzed the flight path and found that the pilot had descended significantly below the altitudes established by the glider club's standard operating procedures. Specifically, while the standard altitude for the windward leg was 1,000 feet, the aircraft was recorded at approximately 779 feet. The investigation focused on why the aircraft experienced an uncommanded increase in its rate of descent during the approach.
Findings
- The primary cause of the accident was the execution of an emergency landing on unprepared terrain due to the aircraft descending below the established traffic pattern altitudes.
- The pilot failed to properly secure the airbrake lever after use, which allowed the airbrake to deploy inadvertently due to aerodynamic forces.
- The pilot did not perform a visual verification to ensure the airbrake was fully retracted and locked.
- The unintended deployment of the airbrake created a descent rate much higher than the pilot had planned.
- The pilot did not monitor the descent rate via instruments or make timely altitude corrections to compensate for the increased drag.