What happened
On April 13, 2006, a Piper PA 23-250 Aztec, registration ZK-FMU, was conducting a multi-engine type conversion training flight near Napier Aerodrome. While the aircraft was in the downwind position of its second circuit, the student pilot attempted to extend the landing gear. During this maneuver, the handle of the landing gear selector lever snapped off in the student's hand.
Because the remaining portion of the lever was stuck inside the control console, the instructor was unable to reach it to manually select the gear down. Furthermore, the aircraft' and two available emergency gear lowering systems were rendered useless because they require the selector lever to be in the down position to function. After consulting with the operator's chief engineer and attempting to manipulate the internal lever with a crash axe, the crew determined a gear-up landing was unavoidable.
The instructor elected to land on the grass portion of runway 07 at Napier Aerodrome to utilize available emergency services. To mitigate damage, the crew shut down the engines and feathered the propellers prior to touchdown. The aircraft touched down smoothly on the grass but slewed 90 degrees when it reached the paved section of the runway. While the belly of the aircraft was scraped and the left propeller was bent, there were no injuries to the student or the instructor.
The investigation
TAIC investigators examined the broken component and found that a fatigue crack had developed at the bend radius of the lever. This crack had progressed to cover approximately 80% of the lever's cross-sectional area. The investigation also noted that the aircraft had undergone a 100-hour inspection just ten days prior, which included a mandatory visual check of the lever for similar cracks.
Findings
- The primary cause of the incident was a pre-existing fatigue crack at the bend radius of the landing gear selector lever, which caused the handle to break during normal operation.
- The emergency gear lowering systems could not be utilized because the selector lever remained in the up position.
- Visual inspections were found to be an unreliable method for detecting the progression of these fatigue cracks, as the crack was likely present but undetected during the recent maintenance check.
Safety action
Following the investigation, the Commission recommended that the Director of Civil Aviation require all operators of the Piper PA 23-250 Aztec to replace the older, susceptible gear selector levers with the improved version (part number 761213) to eliminate the need for repetitive and unreliable visual inspections.