Incident Overview
On July 26, 2005, a Cessna 337-G, registration EC-GDZ, operated by Martínez Ridao, S.A., departed from Son Bonet Aerodrome (Balearic Islands) for a forest fire surveillance flight with two pilots on board. During the approach phase, after selecting the landing gear down, the crew observed that the amber gear-up indicator light remained illuminated and could not see the main landing gear wheels. Multiple attempts to reset the system and to apply the emergency landing gear extension procedure failed. The crew then contacted a company mechanic for advice, followed by Palma Airport Operations at approximately 16:45 local time to declare an emergency due to landing gear failure.
Emergency Response
At Son Bonet, personnel had observed the aircraft make two low passes over the runway with gear doors open and the gear retracted, but were unable to contact the crew. Fire services were alerted. After coordination between Palma and Son Bonet, the emergency was declared and all traffic was instructed to return to Son Bonet before the runway was pre-treated with foam. The decision to apply foam was made jointly by the fire brigade and the pilot. While orbiting to burn off fuel, the crew reviewed emergency procedures and prepared for a gear-up landing.
The aircraft approached Runway 24 at Son Bonet, shut down the front engine as per the flight manual, and then the rear engine when landing was assured. At approximately 18:03 local time, the aircraft touched down smoothly on the foam-covered runway, sliding about 300 meters on its lower fuselage with minimal lateral deviation before coming to a stop. The crew was uninjured, and the aircraft sustained only minor damage.
Post-Flight Inspection
After the aircraft was moved to a hangar, an inspection revealed a hydraulic fluid leak in the nose gear area and an empty hydraulic fluid reservoir. When fluid was refilled and the master switch activated, the hydraulic pump began to operate and fluid was seen leaking from the nose gear door actuator. The retaining clip of the actuator's retainer plug was found displaced from its housing, along with the retainer plug itself, allowing fluid to escape. After reinstalling the plug and clip, and refilling fluid, the master switch caused the hydraulic pump to run and the nose gear extended and locked normally. The actuator was later replaced at the operator's maintenance center.
Investigation Findings
The immediate cause of the incident was the total loss of hydraulic fluid from the nose gear door actuator due to the dislodgement of the retaining clip of the actuator's retainer plug. The exact reason for the clip's dislodgement could not be determined. The actuator had last been overhauled in April 2001, and the retaining clip had not been replaced during the operator's ownership. The manufacturer recommends replacing the clip during actuator overhauls, which are required every five years. The crew's handling of the emergency was described as impeccable, including consulting ground technical personnel, fuel jettisoning, and executing a smooth gear-up landing.
Notably, the report also discusses the use of foam on runways for emergency landings, referencing a previous occurrence involving a similar aircraft (EC-DLS) and a broader trend among operators and airports to discourage foam application due to limited safety benefits and operational challenges.