Accident
On 25 January 2010 at 1358 UTC, a Cessna 421C Golden Eagle, registration N1FY, was landing at Kemble Airfield, Gloucestershire, after an uneventful approach. The Flight Information Service Officer observed the landing gear appear down through binoculars. The aircraft touched down, but the nose gear collapsed, causing the aircraft to slide on its nose until stopping left of the runway centerline. Both occupants—the pilot and a passenger—were uninjured and exited through the rear door. The fire service arrived in less than one minute.
The pilot reported that after selecting gear down, the gear cycled normally and all three green 'down-and-locked' indicator lights illuminated. Even after the collapse, the green lights remained on.
Investigation
Engineering examination by the repair agency found that the nose landing gear downlock had not engaged. The nose gear downlock microswitch was stuck in the closed position due to corrosion. This caused the system to prematurely cut hydraulic pressure to the nose gear actuator, preventing the gear from fully extending and locking. The false indication from the stuck switch also suppressed the 'landing gear unsafe' aural warning.
The aircraft was manufactured in 1981 and equipped with two Continental Motors Corp GTSIO-520 piston engines.
Landing Gear System
The Cessna 421C has a fully retractable tricycle landing gear. Normal extension and retraction are hydraulic, with downlock microswitches on each gear actuator that cut hydraulic pressure when all three indicate 'down-and-locked'. These switches also provide status to cockpit indicators, the hydraulic system, and the aural warning system. An emergency blow-down system is available via an air bottle.
In normal operation, the nose gear locks down before the main gear. If the nose gear microswitch fails closed, hydraulic pressure is removed once the main gears lock, giving a false nose gear indication. This leaves the nose gear partially extended and unable to engage the mechanical downlock latch.
Maintenance and Previous Incidents
The maintenance organization had followed Service Newsletter SNL 89-3, which required sealing downlock microswitches to prevent moisture ingress and corrosion, along with repetitive inspections. The newsletter was mandated by CAA AD 002-02-90 (cancelled in 2003). Additionally, the organization performed annual actuator inspections and replaced sealant every two years as a precaution.
CAA records document several similar accidents involving Cessna 400 series aircraft where nose gears collapsed after false 'down-and-locked' indications. In most cases, corrosion of the downlock microswitch was confirmed.