CEN17FA331 · Beech A36 UNDESIGNAT

The commercial pilot was conducting a business flight; while climbing out after departure, the pilot declared an emergency and reported a loss of engine power to air traffic control. The controller provided vectors to a private airport about 6.5 nautical miles (nm) behind the airplane and stayed in communication with the pilot until communications and radar were lost. The airplane then began a wide turn to head back to the private airport, traveling about 6.3 nm during the turn. The airplane impacted trees and terrain about 6 miles from the private airport. The airplane's maintenance records showed that all six engine cylinders were replaced about 15 months and 227 engine hours before the accident. Postaccident examination of the engine revealed that four of the eight nuts that retained the No. 1 cylinder and one nut that retained the No. 2 cylinder were loose during disassembly, and no breakout torque reading could be measured. Two of the loose nuts on the No. 1 cylinder were on the through-studs that provided clamping force on the No.1 main crankshaft bearing. Disassembly of the crankcase revealed that the No. 1 main bearing had shifted to the rear of the crankcase, which obstructed the oil flow to the No. 1 main bearing and the No. 1 connecting rod bearing. Given the available evidence, it is likely that, during replacement of the engine cylinders, improper torque of the cylinder hold-down bolts and through-studs resulted in an insufficient clamping torque, which allowed the No. 1 main bearing to shift. This shift precluded oil from reaching the No. 1 main bearing and the No. 1 connecting rod bearing, which led to the failure of the connecting rod during the accident flight. The display map data used by the controller handling the flight did not depict another private airport, which was closer (3.4 nm) and was in more of a direct path from the airplane's heading and position at the time of the emergency. The Federal Aviation Administration order governing display map data stated that they should contain airports and heliports among other items, but noted that facility managers could delete items not required. The only exception was that facility managers could not delete airports immediately outside their area of jurisdiction that were within airspace used to receive radar handoffs and that were depicted by the facility having jurisdiction over that airspace. In response to questions from the NTSB, the closer airport was not depicted on the controller’s video display because the air traffic facility was not aware the airport existed. Since the accident, the airport has been added to the display map data. On the basis of the distance that the airplane was able to glide after the pilot declared the emergency (6.3 nm), the airplane should have been able to reach the closer airport that was ahead of it. Thus, the omission of this airport on the controller's display map data resulted in the pilot attempting, at the direction of the controller, to reach an airport that was beyond the airplane's gliding distance.

Verbatim NTSB analysis and probable cause from the NTSB dataset