What happened
On January 21, 2004, a Beechcraft BE 76 Duchess, registration CS-DCS, was performing a flight evaluation involving a student pilot and a flight examiner. The flight, which began at Cascais Municipal Aerodrome, was intended to be a navigation exercise via Porto and Viseu. During the approach to Cascais, the crew noticed that the nose gear "down and locked" indicator failed to illuminate.
Despite attempting to use the manual emergency extension system while flying between 1,0 and 1,500 feet, the nose gear remained retracted. During the procedure, the crew detected a strong burning smell inside the cockpit, suggesting an electrical issue. The flight examiner declared an emergency and decided to land at Cascais on the asphalt runway. To mitigate impact, the crew set the propellers to feather before touchdown. The aircraft landed on its main gear and subsequently slid onto the nose, coming to a halt near the airfield's fire station. The crew escaped without injury, and the aircraft sustained minor damage to the nose cone, gear doors, and forward fuselage bulkhead.
The investigation
The GPIAAF examined the aircraft's landing gear mechanism and the hydraulic system. Investigators found that the nose gear was actually loose and capable of descending, but the gear doors remained closed, physically blocking the extension. The investigation revealed that the hydraulic power pack had failed, with a burnt electric motor caused by high resistance in the pump. Furthermore, the investigation found that the nose gear doors were stuck due to a mechanical issue involving the door actuator linkage.
Findings
- The primary cause of the incident was the improper regulation of the actuator linkage for the nose gear door mechanism. This created a geometric blockage that prevented the doors from opening and subsequently prevented the nose gear from extending.
- A contributing factor was the failure of the electro-hydraulic power pack, which had suffered an electrical burnout.
- The investigation noted that the operator's failure to investigate frequent, recurring nose gear anomalies and the lack of a formal written record of these discrepancies prevented the timely detection of the faulty door regulation.
- The absence of a specific inspection procedure for the gear door actuator linkage in the 100-hour maintenance protocol also contributed to the oversight.