What happened
On May 1, 2024, at approximately 07:09 local time, an ATR 42-500, registration HK-5104, operated by SATENA, was positioned on runway 06 at Gustavo Rojas Pinilla Airport in San Andrés, Colombia. The aircraft was preparing for a scheduled commercial flight to Providencia with 45 passengers and 4 crew members on board.
While the aircraft was stationary at the runway threshold awaiting final cabin confirmation, the nose landing gear (NLG) suddenly retracted. This caused the forward section of the aircraft to drop and make contact with the runway surface. The flight crew immediately alerted the cabin crew and notified air traffic control to request assistance. Following an assessment of the aircraft's condition, the commander ordered the engines to be shut down and initiated an emergency evacuation procedure on the ground. Passengers were disembarked via the main rear door with the assistance of airport firefighters and the Colombian Air Force.
No injuries were reported among the passengers or crew, and no fire occurred. Preliminary inspections of the aircraft revealed minor damage to the nose gear drag brace and gear doors, along with dents on the lower forward fuselage.
The investigation
Investigators from the DIACC, with representation from the French BEA, conducted a field investigation. Initial examinations of the landing gear control lever indicated that only the nose gear appeared unsecured, though crew photographs suggested the right main landing gear (RMLG) also showed an unsecured status at the time of the event.
Subsequent technical testing of the aircraft's systems yielded several critical findings. While initial extension and retraction tests were successful, a specific test involving the nose gear on jacks resulted in an intermittent retraction cycle between the down-unlocked and partially retracted positions, without any input from the crew or ground technicians.
Further analysis of the hydraulic system revealed that the discharge time of hydraulic fluid through the landing gear selector valve (LGSV) during normal operation differed significantly from the discharge times observed during emergency extension tests. This discrepancy was not present in other similar aircraft. Additionally, testing of the multifunction computers (MFC) revealed discrepancies in the values of the weight-on-wheels (WOW) microswitches.