What happened
On July 18, 2022, a Cessna 172 RG, registration CS-DAG, was conducting a navigation training flight from Cascais to Évora. The flight, operated by OATC, was manned by a pilot-instructor and a student pilot. Upon returning to Cascais, the crew was denied a requested VOR procedure due to heavy traffic, leading them to decide on an immediate landing.
During the landing on runway 17, the aircraft was configured with full flaps at an estimated speed of 65 knots. The aircraft touched down on the main gear followed by the nose gear. Shortly after touchdown, the right main landing gear leg began to retract. This caused the aircraft to deviate toward the right edge of the runway. The crew attempted to correct the deviation using left pedal and braking, but the left main gear leg also began to retract. The aircraft eventually came to a halt near the edge of the runway.
There were no injuries to the crew, but the aircraft sustained significant damage to the right horizontal stabilizer, the right rudder, and the right semi-wing tip.
The investigation
The GPIAAF investigation examined the aircraft's systems and maintenance records. Investigators found that the "GEAR PUMP" circuit breaker was in the open position, although the crew did not recall intentionally pulling it. The presence of an audible warning for an unblocked gear was noted during communications both before and after the aircraft stopped on the runway.
Testing of the landing gear control and warning system on jacks showed no anomalies, and the 30A circuit breaker functioned as expected. However, the investigation noted that the aircraft's landing gear was extended at a ground speed between 118 and 124 knots, which, while below the manual's maximum limit, was above the recommended speed for handling gear anomalies.
Findings
- The retraction of the main landing gear during the landing roll was the primary cause of the excursion.
- The open "GEAR PUMP" circuit breaker was a sufficient condition to inhibit the hydraulic pump operation required to lock the gear in the down position.
- The crew's decision to proceed with landing after being denied the VOR procedure precipitated the landing sequence.
- While the aircraft's maintenance records showed no recent anomalies, the operator had previously reported the gear pump circuit breaker tripping in flight, suggesting a latent technical issue that had not been resolved.