What happened
On 15 August 2023, a Piper PA-34-220T, registration G-ZZOT, was conducting a multi-engine instrument rating training flight at Liverpool Airport. The flight involved simulated one engine inoperative (OEI) procedures. Following a successful simulated approach and go-around to Runway 27, the aircraft entered a visual circuit for a subsequent simulated OEI landing.
During the initial go-around, the instructor experienced a loud, persistent warning from the unsafe landing gear system. To facilitate better communication with the student pilot, the instructor pulled the circuit breaker (CB) for the warning system. Although the instructor intended to reset the breaker once the aircraft was downwind, an air traffic control instruction to orbit the airport caused significant distraction.
Due to the increased workload and the complexities of the altered arrival sequence, the landing gear was not lowered, and the circuit breaker was not reset. During the flare of the subsequent approach, the aircraft's propellers struck the runway surface. The instructor immediately applied full power to execute a successful go-around. The aircraft sustained impact damage to both propellers, shock loading to the engines and drivetrains, and minor damage to the fuselage underside. There were no injuries to the two crew members.
The investigation
The AAIB examined the aircraft's warning system and found that the microswitches, which trigger the gear-up alarm based on manifold pressure, were operating within the manufacturer's tolerance range. The investigation established that the instructor had manually inhibited the alarm by pulling the circuit breaker to mitigate communication interference. The investigators also reviewed the operator's procedures regarding the use of circuit breakers during flight.
Findings
- The landing gear remained retracted because the crew failed to complete prescribed pre-landing checks.
- The instructor's decision to pull the circuit breaker to silence a nuisance alarm left the crew without a critical safety alert.
- The instructor failed to reset the circuit breaker due to distractions caused by air traffic control instructions and the high workload of the student pilot.
- Had the landing gear warning system been active, the error likely would have been detected before touchdown.
Safety action
- The operator intended to issue formal guidance stating that circuit breakers should only be pulled when specifically required by an approved abnormal procedure checklist.