Incident Overview
On 18 August 1998 at 1858 UTC, a Beech 76 aircraft (registration G-BNYO) was on a private flight near Bodmin airport. While on the downwind leg, the pilot initiated pre-landing checks and selected the landing gear down. Only two green indicator lights illuminated, indicating the main gear were down but the nose gear was not. The pilot cycled the gear several times, both with normal and emergency extension procedures, but the nose gear remained retracted. A fly-by past the control tower at RAF St Mawgan confirmed the nosewheel was not deployed and the nose doors appeared closed.
Emergency Procedures
The pilot continued to attempt gear extension for about ten more cycles, including application of positive g-force to assist deployment, without success. As daylight diminished and passengers were becoming stressed, the pilot decided to land on the two main wheels. He coordinated with ATC and positioned the aircraft well beyond the threshold of Runway 31, left of centreline to avoid raised runway lights. After a final pull-up, ATC reported the nose doors appeared jammed but slightly open, with the tyre visible above. The pilot briefed passengers, configured for landing with full flap, and at about 400 feet closed throttles to idle, trimmed for 85 kt, and shut down mixtures, master switch, alternators, and magnetos before touchdown. Upon main wheel contact, he turned fuel selectors off and held the nose up as long as possible. Once the nose settled, he unlocked both doors and used brakes to maintain directional control.
Technical Background
The nose landing gear on the Beech 76 incorporates a pin that engages with a fork fitting to actuate the door operating mechanism during retraction. If the pin contacts the lower outside face of the fork instead of engaging correctly, the door mechanism can overtravel and cause the link assembly to go overcentre. In this condition, when gear is selected down, the nose leg begins to lower but is not connected to the fork, so the doors remain locked in the overcentre position, preventing nose gear extension. Improper rigging, stiff door hinges, weak torsion springs, poor lubrication, or sideslipping during retraction can contribute to this mis-engagement. The manufacturer issued Service Instruction No 1209 in May 1983 and Mandatory Service Bulletin No 2310 in October 1989 to address the issue, calling for hinge pin replacement, bushing replacement, and regular lubrication every 60 days or more frequently in severe conditions.
Post-Accident Inspection
After the accident, the door hinges were found to be stiff but had been distorted during the landing. The door link assembly was reported to be correctly adjusted, and inspection did not reveal a specific cause for the malfunction. The requirements of the service instruction and bulletin had been complied with. Between 1982 and the issuance of the mandatory bulletin, five in-flight nose gear failures were reported to the AAIB. This incident was the second reported since the bulletin's introduction; the previous one occurred in January 1994. The evidence suggests the bulletin reduced occurrences, but the mechanism still requires accurate rigging and vigilant maintenance to ensure free operation.