What happened
On May 26, 2012, a Socata ST-10, registration PT-DMC, was performing a ferry flight from Sorocaba to Tatuí, Brazil, carrying a pilot and one passenger. Approximately ten minutes after takeoff, the aircraft's electrical system began experiencing intermittent failures, affecting various instruments.
While the pilot successfully deployed the landing gear using the normal system, the electrical failure prevented the cockpit indicator lights from confirming that the gear was locked in place. Consequently, the pilot executed emergency procedures to ensure the gear was down. Due to a lack of radio communication, the pilot used a mobile phone to contact individuals at the destination to assist in verifying the gear status.
Upon landing at runway 32 of the Tatuí Aerodrome, the landing gear retracted during the landing roll. The aircraft slid approximately 260 meters along the runway before coming to a stop on the left side of the pavement. The aircraft sustained substantial damage to the propeller blades and landing gear, along with minor damage to the lower fuselage. Both occupants were uninjured.
The investigation
The CENIPA investigation focused on the simultaneous occurrence of two independent mechanical and electrical failures. Investigators determined that a faulty battery relay had caused the electrical instability, which specifically resulted in the loss of the three green landing gear indicator lights.
Upon further inspection of the aircraft, investigators found that the landing gear control cables—specifically the flexball type—were malfunctioning. A misplaced stainless steel ball within the cable assembly caused the cable for the left main gear to jam. Because the control cables are interconnected, this jam created resistance in the emergency manual extension crank, providing the pilot with a false sensation that the gear was properly extended and locked.
Additionally, the investigation revealed that while the aircraft held a valid airworthiness certificate, the maintenance logs for the airframe, engine, and propeller were not up to date, specifically lacking recent monthly usage records.
Findings
- Maintenance of the aircraft
- A faulty battery relay caused the loss of visual landing gear position indicators.
- A misplaced internal component in the landing gear control cable caused a mechanical jam, leading to the false indication of gear lock during emergency deployment.