What happened
On 27 February 2019, a modified Spitfire Mk.T IX, registration G-CTIX, was performing a private flight at Denham Airfield in Buckinghamshire. During the approach to land on the grass runway, the pilot selected the undercarriage down. Although the green indicator light illuminated and the pilot felt the gear lock into place, the undercarriage warning horn began to sound once the flaps were deployed.
Having previously experienced the warning horn sounding erroneously during takeoff in this specific aircraft, the pilot believed the horn was malfunctioning and relied on the cockpit's green light indication. The aircraft touched down in a 3-point attitude and began its ground roll. However, at approximately 30 mph, the right wingtip began to drop. The pilot realized the right undercarriage leg was retracting, causing the propeller to strike the ground. The aircraft eventually came to rest upright after the left undercarriage leg also failed, causing the aircraft to tilt. There were no injuries to the pilot or the passenger.
The investigation
Investigators examined the aircraft's undercarriage and indication systems to determine why the gear failed to remain locked. The inspection of G-CTered IX revealed that the right undercarriage leg had not been properly locked down. Specifically, the right down position switch was found to be stuck in the closed position, which provided a false green light indication to the cockpit even though the locking pin had not engaged.
Further examination of the aircraft's mechanics suggested that the undercarriage may not have been fully seated due to either an incomplete lever selection or excessive aerodynamic loads preventing the locking pin from engaging. The investigation also noted that the aircraft's warning horn system was configured differently than many other Spitfire variants, contributing to the pilot's misunderstanding of the cockpit alerts.
Findings
- The right main undercarriage was not secured in the locked position and retracted during the landing roll.
- A faulty down position switch on the right side remained stuck in the closed position, providing a false indication that the gear was safe.
- The pilot's reliance on the green light, driven by previous experiences with spurious horn alerts in this specific aircraft, prevented him from recognizing the gear was unsafe.
- The undercarriage may have failed to lock due to incomplete lever movement or aerodynamic forces preventing the locking pin from engaging.