ERA23LA253

The pilot reported that the purpose of the flight was to test the newly installed autopilot servos and calibrate the fuel flow sensor. The pilot stated that the control surfaces moved as expected during the preflight inspection. Near the end of the flight, the autopilot did not turn to a programmed waypoint. The pilot disconnected the autopilot and took over manual control of the airplane but was unable to prevent an unintended nose-down pitch. Despite verifying the autopilot disconnection, the yoke was unresponsive and the airplane continued to descend on the final approach, striking a light pole about 1,000 ft short of the runway threshold before impacting the ground. Postaccident examination of the airplane revealed that the pitch servo bridle cable clamp had not been properly installed, which resulted in the cable binding when the yoke was pulled aft. The installer had not verified that the required clearance was maintained and did not perform the necessary post-installation control movement checks as specified in the autopilot’s installation instructions. The incorrect positioning of the bridle cable clamp resulted in restricted elevator control, which prevented the pilot from recovering from the nose-down condition during the approach.

On June 1, 2023, about 1455 eastern daylight time, a Beech V35A, N8074R, was substantially damaged when it was involved in an accident near Statesboro County Airport (TBR), Statesboro, Georgia. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he was testing the function of newly installed servos for the Garmin GFC-500 autopilot and calibrating the fuel flow sensor. During the preflight inspection, he moved the yoke and checked all control surface movements. He programmed the flight director, setting a cruising altitude of 3,000 ft with a pitch climb between 5° and 7°. During the takeoff roll, the pilot noted the controls felt "slightly heavy" and adjusted the ruddervator trim to nose-up using the electric trim switch. After liftoff, he engaged the autopilot, and the airplane climbed and maintained 3,000 ft. Throughout the flight, the pilot issued heading change commands via the GFC-500 display. After about an hour, the pilot programmed the autopilot to descend to 2,000 ft in preparation for landing at TBR. However, the autopilot failed to intercept the waypoint he had set. He disconnected the autopilot and assumed manual control. While on approach, he noticed the airplane was descending to an altitude lower than intended. He applied power, but the nose suddenly pitched down. Despite verifying that the autopilot was disconnected, he was unable to move the yoke aft. The airplane continued descending and he struggled to regain control. On the final approach, the airplane impacted a light pole about 1,000 ft short of the runway threshold before colliding with the ground and coming to a stop. Postaccident examination of the airplane revealed an anomaly with the pitch servo bridle cable installation. The bridle cable clamp’s swaged ball fitting was positioned at the 1 o’clock position with the yoke in a full-forward position. However, installation instructions in the GFC 500 Installation Manual Addendum specified that the swaged ball should be at 1 o’clock with the yoke in the neutral position—defined as 4.5 inches aft of the instrument panel, per the Bonanza 35 Series Shop Manual, Page 3-6C (Elevator Rigging Procedure, Serials D-5726 and after). This installation resulted in the bridle cable clamp being positioned on the upper elevator cable such that it would bind against the former rib at flight station (F.S.) 179 when the yoke was pulled aft. Further examination determined that the installer did not verify the required .5- to 1-inch clearance between the bridle cable clamp and F.S. 179 when the elevator was in the full-up position, as specified in the installation manual addendum. Additionally, the installer did not follow the required procedures outlined in the GFC 500 Autopilot with ESP Part 23 AML Installation Manual, paragraph 4.2.1 (Page 45), which required: 1. Moving the flight controls through their full range of travel after servoinstallation and cable tensioning. 2. Ensuring that flight control surfaces move freely from stop to stop. 3. Verifying that no binding or restriction of flight controls resulted from the servo installation. 4. Confirming that servo cables, cable clamps, and main flight control cables maintained adequate clearance from adjacent structures and feed-through holes throughout the full range of motion. During an interview, the personnel from the maintenance facility who performed the installation acknowledged that the GFC-500 installation had been performed incorrectly.