What happened
On 19 July 2016, a Socata TB20 Trinidad GT, registration G-SCIP, was performing a private flight from Goodwood to Welshpool. Following takeoff, the pilot noticed that the nose gear 'down and locked' green light remained illuminated, even though the 'in-transit' light had turned off. Suspecting a sticking microswitch, the pilot continued toward the destination.
To verify the gear status, the pilot performed a low pass over Welshpool. While the radio operator initially thought the gear appeared retracted, the green light remained on. Subsequent attempts to extend the gear showed the indicator light remained green, yet the pilot could not feel the gear lock into place via the rudder pedals. During a further low pass, the radio operator observed the nose gear being pushed backward by the airflow.
Deciding to divert to Sleap Airfield, the pilot attempted to force the gear into position by cycling the lever and pulling 'g' loads. Upon approaching Sleap, the green light continued to show the gear as locked despite the physical failure of the mechanism. During the final landing approach, the pilot shut down the engine at approximately 50 feet to prevent propeller damage. As the aircraft touched down on the main wheels, the nose gear collapsed, causing the aircraft to strike the runway surface. There were no injuries to the pilot.
The investigation
The AAIB examined the nose gear downlock microswitch assembly. Testing revealed that the electrical outputs from the switch were random. Further analysis, conducted in coordination with the French BEA, involved X-raying and disassembling the unit. The investigation found that the internal components of the microswitch assembly were disrupted; specifically, the metal plates were loose and a spring had become jammed under a plate. The manufacturer suggested that such internal damage was likely the result of a severe impact.
Findings
- The nose gear downlock microswitches were malfunctioning, providing random electrical signals.
- The green 'down and locked' light remained illuminated despite the gear not being physically locked.
- Internal components of the microswitch assembly were loose or jammed, likely due to a previous high-impact event.
- The pilot's decision to shut down the engine during the final approach was intended to protect the propeller from damage during the anticipated nose gear collapse.