What happened
On July 26, 2005, a Cessna 337-G, registration EC-GDZ, was conducting a forest fire surveillance flight when the crew encountered a landing gear malfunction. While entering the traffic pattern for runway 24 at Son Bonet Aerodrome, the crew observed that the amber gear-up light remained illuminated and the main landing gear was not visible. Despite attempting to reset the system and following emergency extension procedures, the gear failed to deploy.
The crew consulted with a company mechanic and subsequently declared an emergency with Palma Airport Operations. To prepare for the landing, the crew flew patterns to consume excess fuel. Following established emergency procedures for a gear-up arrival, the crew shut down the front engine prior to touchdown and subsequently shut down the rear engine once the aircraft was on the ground. The aircraft landed smoothly on a runway surface that had been pre-treated with foam by airport firefighters. The Cessuna 337-G slid approximately 300 meters on its lower fuselage, remaining largely on the runway centerline. The two crew members were uninjured, and the aircraft sustained minor damage.
The investigation
Investigators examined the aircraft's hydraulic system and discovered that the hydraulic fluid reservoir was empty due to a leak in the nose gear door actuator. Upon replenishing the fluid, the leak was traced to the nose gear door actuator's retaining plug. The investigation established that the retaining clip for this plug had become displaced from its housing, allowing fluid to escape.
While the aircraft had undergone recent inspections, the specific component—the actuator retaining clip—had not been replaced during the period the aircraft was operated by the current company. Maintenance manuals indicate that such clips should be replaced during actuator overhauls, which occur every five years; the last overhaul for this specific actuator had taken place in April 2001.
Findings
- The immediate cause of the incident was the total loss of hydraulic fluid caused by a leak in the nose gear door actuator.
- The leak was triggered by the displacement of the retaining clip from the actuator's retaining plug.
- The manual emergency pump was ineffective because the hydraulic fluid level had dropped below the level required for the pump to operate.
- The crew's management of the emergency, including coordination with ground personnel and the decision to use the foam-covered runway, was effective.