What happened
On August 25, 2018, at 15:22 local time, a Beechcraft 3 TM Model 18, registration N184KP, was performing a landing at Grenchen Airport (LSZG) under Visual Flight Rules. The aircraft was completing a local flight when, during the landing roll on runway 24, the pilot discovered that the left main wheel brake was non-functional. At the time of the incident, the wind was recorded at 12 knots from 2/80 degrees. Due to the loss of braking capability, the aircraft traveled approximately 400 meters along the runway before veering right and coming to a stop on the grass area. There were no injuries to the pilot, and the aircraft sustained no damage.
The investigation
Technical inspections following the excursion revealed that the connecting bolt between the left rudder pedal and the left brake cylinder had detached. The bolt, along with its associated castle nut and washer, were found on the cockpit floor beneath the rudder pedals. Investigators noted that the cotter pin required to secure the castle nut was missing. A similar condition was observed on the right side, where the connecting bolt between the rudder pedal and brake cylinder also lacked a cotter pin, although the nut had not yet loosened on that side.
Findings
- The primary cause of the brake failure was the absence of cotter pins on the connecting bolts, which allowed the hardware to vibrate loose over time.
- It is highly probable that the cotter pins were omitted during the most recent installation of these bolts.
- The loss of the left brake prevented the pilot from maintaining directional control during the landing roll, particularly as tailwheel aircraft often require active braking to counteract side-wind components and maintain centerline.
- The last annual inspection occurred in spring 2018, but this specific component does not necessarily require disconnection during such a check.