What happened
On July 27, 2023, a Diamond DA42, registration PH-TCD, was conducting a local training flight at Ponte de Sôr (LPSO), Portugal. The flight, operated by SEVENAIR, was manned by a flight instructor and a student pilot. After completing six successful touch-and-go maneuvers, the aircraft experienced a hard landing during the seventh circuit.
The impact caused the left main landing gear (MLG) condition lights to switch from green to red, indicating an unsafe condition. Although the crew attempted to recycle the landing gear, the red warning light remained illuminated. The instructor decided to proceed with a landing attempt. During the landing on runway 03, the left main gear failed to lock in the down position, causing the aircraft to veer off the left edge of the runway.
Both occupants escaped the aircraft without injury. However, the aircraft sustained substantial damage, including significant impact to the lower fuselage, flaps, engine cowlings, propellers, canopy, and the primary structure of both wings.
The investigation
The GPIAAF investigation examined the aircraft's maintenance history and the mechanical failure of the landing gear. Investigators found that the hard landing had caused the drag brace ribs on both main landing gear legs to debond from the wing main box, which physically prevented the gear from locking.
The investigation also reviewed the aircraft's maintenance records, noting that the operator had been applying a 10% extension to certain inspection intervals, a practice that exceeded the +/- 50-hour tolerance permitted by the aircraft manuals. Furthermore, while maintenance instructions require structural findings to be reported to the manufacturer after Major Structural Inspections (MSI), no evidence of such reporting was found for this aircraft.
Findings
- The hard landing caused structural damage to the landing gear attachment points, specifically the debonding of the drag brace ribs.
- The flight instructor's decision to land with the gear in an unsafe, unlocked state deviated from the Aircraft Flight Manual (AFM) procedures, which instruct the crew to perform a landing with the gear retracted if manual extension fails.
- The aircraft's high-utilization training profile involves frequent landing cycles, which may necessitate more frequent structural inspections than those currently established by the manufacturer's hour-based program.
- Inconsistencies were identified in the maintenance program, specifically the unauthorized 10% extension of inspection intervals and a lack of documented communication with the manufacturer regarding structural findings.