WPR24LA034

According to the pilot, who did not hold a multi-engine rating, as the airplane climbed through 4,500 ft msl, he noted that the manifold pressure gauge showed asymmetric manifold pressure readings between the two engines; the left engine appeared unresponsive and could not be reduced below 21 inches of mercury with movement of the throttle lever. The pilot briefly attempted to troubleshoot the unresponsive engine before he decided to return to the departure airport for landing. During the final approach, the airspeed decayed to 80 mph. The pilot stated that he “pushed the props forward instantly;” however, the airplane immediately rolled left and the stall horn sounded as it descended into terrain. A video recording from a surveillance camera showed the airplane bank left and right before it pitched up, rolled to the left, and descended out of view of the camera. Witnesses near the accident site reported that the airplane appeared slow while on approach to landing. One witness, who responded to the accident site, reported that the pilot told him that the “throttle stuck.” Postaccident examination of the engines did not reveal any preimpact mechanical failures or malfunctions that would have precluded normal operation. Additionally, both the left and right propellers exhibited chordwise, rotational scoring, which was consistent with both propellers rotating at impact. Examination of the airframe revealed that the hardware used to attach the left engine throttle cable to its mounting bracket did not conform to the manufacturer's design. Instead of the throttle conduit, which houses the throttle cable, secured using a singular rubber-cushioned support clamp, the accident airplane had a piece of aluminum tubing wrapped around and affixed to the outside of the throttle cable conduit with 2 worm-drive band clamps. The throttle cable and aluminum portion were attached to the bracket with a rubber cushioned support clamp. When the throttle cable was moved by hand, the cable, aluminum, and cable conduit slid through the support clamp. This installation likely allowed the throttle cable assembly to move though the support clamp freely, with either band clamp moving against the support clamp or throttle conduit securement nut, restricting the movement of the travel of the throttle cable itself, or inducing enough slack within the throttle cable to not rotate the throttle control arm on the fuel control when the cockpit control throttle control lever was moved. Because the airplane’s maintenance records were not made available for review, the investigation could not determine when the left-engine throttle cable assembly was repaired and modified from the original design.

On November 13, 2023, about 0800 Pacific standard time, a Cessna 310D, N86H, was substantially damaged when it was involved in an accident near Hayden, Idaho. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, who did not possess an airplane class multi-engine rating, reported that he had departed Coeur d'Alene Airport - Pappy Boyington Field (COE), Hayden, Idaho, with an intended destination of Nampa, Idaho. As the airplane climbed through 4,500 ft, the pilot retarded both engine throttles and noticed the left engine manifold pressure would not decrease below 21 inches. Despite his efforts to troubleshoot the difference in manifold pressure between the two engines, he was unsuccessful and the left engine was unresponsive. The pilot decided to return to COE for a precautionary landing. While on final approach, as the airplane neared the approach end of runway 2, the airspeed decayed to 80 mph, and the pilot “pushed props to full instantly.” Subsequently, the airplane began to roll left and the stall horn sounded. The pilot reported that he applied rudder and aileron inputs before he lowered the nose until the airplane impacted terrain. A security camera video at a nearby business captured the airplane on approach. As the airplane overflew a road located about 1,000 ft from the approach end of runway 2, the airplane pitched up and began to bank left and right. The airplane subsequently rolled to the left and pitched downward as it descended from view behind a building. Several witnesses stated the airplane appeared slow during the approach before it pitched up, rolled left, and impacted terrain. According to a first responder who treated the pilot at the accident site, the pilot told him that “the throttle stuck.” Postaccident examination of the wreckage revealed the fuselage and wings sustained impact damage, the empennage had partially separated from the fuselage, and the engines had separated from the engine nacelles. The engine throttle, propeller, and right mixture levers were found positioned fully forward, and the left mixture lever was found in the idle-cutoff position. Examination the engines did not reveal any evidence of a preexisting mechanical malfunction that would have precluded normal operation. During examination of the left engine, the installation of the left throttle control cable end had a piece of sectioned aluminum tubing wrapped around and affixed to the outside of the throttle control cable conduit and throttle cable with 2 metal worm-drive hose clamps. The entire throttle cable assembly was attached to a bracket with a rubber-cushioned support clamp, as seen in figure 1. When the throttle cable was moved by hand, the throttle cable, aluminum piece, and throttle conduit slid through the support clamp. The maintenance manual and parts catalog showed that the throttle cable is normally housed within a conduit and attached to the bracketwith a support clamp. Figure 1: Left engine throttle cable installation (Photo courtesy of Textron Aviation, with NTSB annotations) The airplane’s maintenance records were not made available for review, and it was not determined when the repair on the throttle cable had been performed.