Accident Overview
On September 11, 1997, at approximately 1645 local time, a Cessna F 177 RG (registration HB-CGM) operated by a private owner was conducting a check flight from Birrfeld airfield. The pilot was accompanied by a mechanic from the maintenance facility. The purpose of the flight was to verify the correction of irregularities noted earlier in the nose wheel steering and rudder trim.
Flight Sequence
During taxi, the nose wheel steering functioned normally. Takeoff and climb were uneventful. At 4000 ft, the rudder trim was tested in cruise configuration and found satisfactory. After about 20 minutes, the pilot returned to the airfield. As the aircraft descended with flaps set to 10° and the landing gear lever in the "down" position, both occupants observed that the main gear had extended but the green indicator light did not illuminate. Repeated cycling of the gear, including manual extension attempts, did not resolve the issue. While the mechanic coordinated troubleshooting via radio with the maintenance facility, another aircraft reported that the nose gear appeared retracted and all gear doors were closed. The pilot decided to land on grass runway 26. On short final, he shut down the engine, turned off ignition and master switch, and closed the fuel valve. With the propeller horizontal, the aircraft touched down softly at approximately 1815 hours, slowly pitched forward onto its nose, and came to a stop after a short roll.
Injuries and Damage
No persons were injured. The aircraft sustained damage to the forward lower engine cowling, the gear doors, and the exhaust system.
Investigation Findings
- The pilot held a valid private pilot license with sufficient total flight experience (675 hours) and recent training. No evidence of medical impairment was found.
- The aircraft was properly maintained; the last 200-hour inspection was completed on September 11, 1997 at 1803 flight hours.
- Weight and balance were within prescribed limits.
- An earlier incident on May 5, 1989, involved the nose gear collapsing during landing at Bern. That repair was performed by a local maintenance facility. No similar issues were reported in the intervening period.
- During recovery, the nose gear could be extended using the aircraft's own system, which remained undamaged. The only damage was to the gear doors and exhaust. This allowed thorough examination of the nose gear system in the accident condition.
- When the aircraft was jacked, the entire landing gear cycled normally through numerous extensions and retractions using the aircraft's electro-hydraulic system. However, examination revealed that a lever (part of the bellcrank assembly) was slightly bent and showed rubbing marks. Additionally, the cam follower (a roller on the lock assembly) was incorrectly assembled: the washer was positioned between the roller and its carrier instead of between the carrier and the nut.
- If the uplock hook is not released or not fully released, neither gravity nor hydraulic force can extend the nose gear. This condition was simulated by manual intervention.
Assessment
The pilot and mechanic acted correctly and took sufficient time to troubleshoot. However, due to the nose gear being blocked in the retracted position, none of the attempted remedies succeeded. The blockage likely resulted from the interaction between the cam follower roller and the lever. The incorrect washer placement created a gap that allowed the lever to catch, disrupting the proper release of the uplock hook. The rubbing marks and deformation of the lever indicated that the unlocking function was not proceeding normally due to mechanical deficiencies (imprecise rolling contact between lever and roller). It could not be determined whether the faulty assembly originated from the 1989 repair or from later maintenance. The nose gear system requires very precise adjustment for proper function, which also explains why the gear could be extended after the landing had induced strong vibrations.
Probable Cause
The accident is attributed to blocking of the nose gear in the retracted position, likely due to faulty assembly of a part (cam follower) in the system.