What happened
On June 15, 1995, a Cessna Centurion 210L, registered as HB-CHZ, was conducting flight training operations at Neuchâtel Aerodrome. The aircraft, operated by the Club Neuchâtelois d’Aviation, had been used earlier that morning for instructional purposes involving various configurations and simulated emergencies. During these morning sessions, an instructor intentionally tripped the circuit breaker for the landing gear system to demonstrate the manual extension procedure, which functioned correctly at that time.
Around 14:00 local time, the aircraft departed on a circuit training flight with a student pilot at the controls and a professional instructor acting as the pilot in command. After retracting the landing gear following takeoff, the instructor observed that the green "down and locked" indicator light remained illuminated despite the lever being moved to the "up" position. Following instructions from the instructor, the student attempted to cycle the gear again, but the system failed to operate normally. As they approached the final stage of the traffic pattern, the student selected the gear down position, yet no deployment occurred.
After verifying that the circuit breaker was in place and repeating the electrical cycling attempts without success, the student initiated the manual emergency extension procedure. During this process, both crew members noted that the physical effort required to pump the handle was significantly higher than during the morning's demonstration. The instructor then took control of the emergency handle but found that the gear would not extend further. Contact was established with the aircraft's maintenance team on the ground, who advised a series of checks and manipulations. Despite these efforts, the nose gear remained retracted while the main gear eventually extended partially.
With assistance from ground personnel coordinating an emergency response for a grass runway landing, the crew prepared for a belly landing. The instructor executed the approach and touched down on the main wheels on the grass strip adjacent to runway 23. The aircraft slid forward on its nose for several dozen meters before coming to a stop. Both occupants exited the aircraft unharmed, and no fire ensued.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the technical condition of the aircraft and the operational context of the flight. The Cessna HB-CHZ had accumulated 2,365 flight hours and 3,050 landings at the time of the incident. Technical inspections conducted on June 19, 1995, revealed a defect in the landing gear system's electrical wiring.
The investigation focused on the hydraulic and electrical components responsible for the nose gear door actuation. It was determined that the insulation on a wire supplying power to the nose gear door control valve had been stripped. This exposed conductor came into contact with the positive terminal of the relay controlling the landing gear motor. This short circuit prevented the valve from operating correctly after the gear was retracted, effectively locking the system in a state where the nose gear doors remained closed.
The investigation also reviewed the operational timeline. The crew had maintained radio contact with maintenance throughout the incident, allowing for a prolonged period of troubleshooting. The ground team eventually authorized the crew to continue pumping the emergency handle despite the abnormal resistance, which allowed the main gear to fully extend. However, because the nose gear door mechanism remained electrically locked, the nose wheel could not deploy.
Findings
The primary cause of the accident was an electrical fault that prevented the complete extension of the landing gear. Specifically, a damaged wire in the nose gear door control circuit created a short to ground, inhibiting the hydraulic pressure from opening the nose gear doors. Consequently, the nose gear was mechanically blocked from extending even when the manual pump was used.
Contributing factors included:
- The failure of the electrical system to allow the nose gear door actuator to function after retraction.
- The lack of a specific checklist item for cutting general electrical power to reset the system, which might have resolved the issue.
- The increased resistance felt during manual pumping was due to the main gear struts being partially extended and pressurized, while the nose gear remained locked.
The crew's handling of the emergency was deemed appropriate. They managed fuel effectively, maintained communication with maintenance, and executed a controlled landing on the grass strip without endangering themselves.
Safety action
The investigation highlighted that the damaged wire may have resulted from previous impacts sustained by the aircraft during earlier accidents in 1992 and 1994. While no specific safety recommendations were issued in this final report regarding procedural changes, the incident underscored the importance of thorough inspections of electrical wiring following structural damage or hard landings.