What happened
On 31 October 2009, a private flight involving a Ravin 500, registration ZU-XML, was returning to Wonderboom Aerodrome (FAWB) in Gauteng. The pilot had been conducting a period of flight testing to monitor engine performance and autopilot configurations. As the pilot joined the right downwind for Runway 21, they attempted to extend the landing gear.
Upon moving the undercarriage lever, the electro-hydraulic actuator engaged for an unusually long duration without the three green lights indicating the gear was locked. Shortly after, a circuit breaker tripped, and the undercarriage unsafe light illuminated. Despite various attempts to resolve the issue—including flying at 7,000 feet to use hydraulic pressure, manual pressure, and even creating negative G-forces—the gear remained stuck. Unable to extend the nose gear, the pilot performed a low-level runway inspection and executed a wheels-up landing on Runway 29. During the touchdown, the propeller blades struck the tarmac, causing significant damage to the propeller, the nose wheel, and the lower fuselage.
The investigation
SACAA AIID examined the aircraft and the mechanical components of the landing gear assembly. The investigation focused on why the hydraulic actuator failed to complete the extension cycle. Technical inspections were conducted by the manufacturer to analyze the internal components of the nose wheel strut.
Findings
- The investigation established that a trunnion bush located inside the nosewheel strut was sticking, which caused the piston to seize.
- This seizure prevented the nose strut from fully extending, which in turn prevented the gear from locking into place.
- While physical evidence confirmed that an obstruction was present between the trunnion bush and the cylinder, the specific nature of the debris could not be definitively identified.
- There was a suspicion that fragments from a previously replaced nitrogen charging valve might have entered the system, but this remained unconfirmed.
- The pilot was properly licensed and medically fit, and the weather conditions were clear with good visibility.
- The aircraft was relatively new, with only 15 total airframe hours at the time of the accident.