Synopsis
On July 27, 2023, at 11:36 UTC, a Diamond DA42 aircraft, registration PH-TCD, operated by Sevenair, was conducting a local training flight at Ponte de Sôr (LPSO), Portugal. The flight instructor and student pilot onboard performed six touch-and-go maneuvers without any reported anomalies. During the seventh circuit, a hard landing occurred on the left main landing gear (MLG), causing the left MLG condition lights to turn off and the red 'unsafe condition' light to illuminate. The instructor decided to continue down the runway at about 80 knots and take off to attempt another approach.
Occurrence
After takeoff, a landing gear recycle was attempted, followed by gear down selection, but the red unsafe light remained on. A low pass was performed to receive input from the flight information service regarding the gear down condition, which was confirmed. During the subsequent landing on runway 03 with the left main gear not locked down, the aircraft exited the runway off the left edge. The estimated wind at LPSO was northwest at 9 knots.
Injuries and Damage
Both occupants egressed the aircraft safely without injuries. The aircraft sustained significant damage to the lower fuselage, flaps, both wings' primary structure, both engine cowlings, propellers, and canopy.
Relevant Findings
The flight crew was duly authorized for the flight. The instructor pilot had 2,604.33 total flight hours, 783.25 hours on twin-engine aircraft, and 76.55 hours as an instructor on the accident aircraft type. The student pilot had 154.15 total flight hours, with 23.15 hours on the type. No medical conditions negatively influenced the occurrence.
The Diamond DA42 is a twin-engine, four-seat, low-wing monoplane with a composite structure and hydraulically operated tricycle retractable landing gear. The aircraft had accumulated 9,998.40 flight hours at the time of the event. Scheduled maintenance inspections were based solely on flight hours, without requirements for landing cycle counting.
Post-event evidence gathering included analysis of communications between the aircraft and the air traffic information service. An audible warning of the unlocked gear was noted during landing instructions. The operator and original equipment manufacturer (OEM) assessed the aircraft condition; they attributed the left MLG not locking to damage on both MLG drag brace ribs, which debonded from the wing main box during the hard landing on the seventh circuit, preventing system operation.
The Aircraft Flight Manual (AFM) section 3.6.1 addresses the landing gear unsafe condition and requires manual extension. If the gear cannot be extended to the down and locked position, AFM section 3.6.3 instructs landing with the gear up. The flight instructor did not detail the decision-making process for proceeding with landing in an unsafe gear condition.
Regarding the Major Structural Inspection (MSI), the operator reported that the 6,000-flight-hour inspection was carried out on July 3, 2014, when the aircraft had 5,989.00 flight hours. The recurrent 4,000-hour inspection would be completed by 10,389.00 flight hours, with a 10% extension allocated.
GPIAAF Comments
The hard landing likely caused damage to both MLG drag brace ribs, preventing correct operation of the left landing gear system. The aircraft's standard operating procedures and AFM define mitigation actions for an uncommanded gear-up condition, which should be strictly followed. The manufacturer determined that landing with the gear up is the prescribed procedure for an irreversible gear-not-locked-down condition, based on analysis of potential consequences of loss of control. The instructor's decision to land with the gear down and unlocked exposed the aircraft to risks.