Accident Details
On July 29, 2013, at about 1935 eastern daylight time, a Mooney M20J, registration N4570H, sustained substantial damage during a forced landing following a partial loss of engine power near Leonardtown, Maryland. The airline transport pilot (ATP) rated pilot and an ATP rated flight instructor sustained minor injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a local instructional flight; no flight plan was filed. Visual meteorological conditions prevailed. The flight departed St. Mary's County Regional Airport (2W6) in Leonardtown at about 1850.
According to the pilots, while practicing instrument maneuvers at about 1500 feet above mean sea level, the engine stopped responding to throttle control inputs and did not produce enough power to maintain level flight. They turned toward 2W6 and searched for a suitable landing area. The flight instructor attempted to restore engine power by activating the fuel boost pump, switching the fuel selector to the alternate tank, and adjusting the throttle position. The pilots then elected to land in a field. During the landing, the airplane impacted the ground, struck a fence line, and came to rest in a corn field.
Pilot Information
The pilot flying held an ATP certificate for airplane multiengine land, a commercial certificate for airplane single-engine land, and a flight instructor certificate for airplane single-engine, multiengine, and instrument airplane. His most recent second-class medical certificate was issued on January 14, 2013. He reported 6849 total flight hours, with 316 hours in the same make and model as the accident airplane.
The flight instructor held an ATP certificate for airplane multiengine land, a commercial certificate for airplane single-engine land, and a flight instructor certificate for airplane single-engine, multiengine, and instrument airplane. His most recent second-class medical certificate was issued on May 31, 2013. He reported 3597 total flight hours, with 82 hours in the same make and model.
Aircraft Information
The airplane was issued an airworthiness certificate on July 23, 1976. It was equipped with a Lycoming IO-360-A3B6D engine, serial number L-15188-51A. A review of maintenance logbooks showed an annual inspection was completed on April 15, 2013, at a recorded tachometer reading of 5276.8 hours. At that time, the mechanic reported that all engine control cables were "checked" and lubricated. The tachometer at the accident site indicated 5302.9 hours. The most recent maintenance was performed on July 23, 2013, when the starter was removed, overhauled, and reinstalled at a tachometer time of 5301.9 hours.
Postaccident Examination
A Federal Aviation Administration (FAA) inspector examined the airplane after the accident and found that both wings and the fuselage sustained substantial damage. However, due to the accident location, the inspector could not remove the cowlings to examine the engine further.
One of the airplane owners inspected the aircraft prior to wreckage recovery. He removed the engine cowling and discovered a bolt and nut resting on the bottom of the cowling. He also noted that the throttle arm linkage was not connected to the throttle body arm. The throttle linkage was in the full forward position, while the throttle body arm was in the low power setting. He asked an individual to move the throttle in the cockpit; the throttle linkage moved but the throttle body arm did not.
An interview with the mechanic who performed the annual inspection and starter work revealed that the bolt and cotter key were in place on the throttle linkage and throttle body arm at the time of the annual inspection. He stated that the starter work was performed on the opposite side of the engine from the throttle body and that the throttle linkage was not removed during the starter change. The mechanic could not explain how the linkage became disconnected and noted that after the aircraft landed gear-up, hit a fence, and spun, the missing bolt could have come to rest directly below the connection point.
Engine Test Run
A postaccident engine test run was conducted under National Transportation Safety Board (NTSB) supervision using the fuel on board at the time of the accident. An undamaged propeller was installed, a battery from another airplane was attached, and a bolt was installed to connect the throttle cable to the throttle control arm. The engine started on the second attempt; the first attempt failed due to an undercharged battery. The engine accelerated to 1700 rpm without hesitation. A magneto check revealed no anomalies. The engine was reduced to idle and ran smoothly. No anomalies or mechanical malfunctions were noted during the engine run that would have precluded normal operation.