Accident Details
On Wednesday, March 15, 2006, at 16:15 local time, at Cuatro Vientos Airport (Madrid), a Cessna FR-172-J, registration EC-GOZ, experienced an unintended engine start while the pilot was manually turning the propeller. The aircraft accelerated rapidly, struck a parked aircraft (EC-IEH), and then a third aircraft (EC-CSX). The pilot did not sustain any injuries. The two parked aircraft sustained damage: EC-IEH and EC-GOZ suffered substantial damage, while EC-CSX had minor damage.
Aircraft and Personnel
The aircraft was a Cessna FR-172-J, powered by a single Continental IO-360-H engine. It was privately operated. The pilot, aged 37, held a private pilot license and a valid Class 2 medical certificate. He had accumulated approximately 130 total flight hours, all on the accident aircraft type. His last flight was about eight months prior.
Sequence of Events
The pilot planned a flight from Cuatro Vientos to Fuentemilanos Aerodrome with two passengers. To start the engine, he primed the fuel system at least six times, set the throttle to about 1/4 open, and the mixture to rich. The battery was low because the aircraft had not been used for over a month; the engine would not start. All three occupants exited the aircraft. The pilot believed he had set the parking brake and left the magneto switch in the OFF position. The throttle and mixture remained in the positions used during the start attempt.
While the passengers went to obtain a ground power unit, the pilot manually rotated the propeller. This caused the engine to start. The aircraft immediately accelerated. The pilot could not climb aboard to apply brakes. The aircraft moved uncontrolled across the apron, striking the left wing of the parked aircraft EC-IEH with its propeller and right wing. The two aircraft became entangled. With the EC-GOZ engine still running, the motion of both aircraft caused the nose of EC-IEH to strike the left wingtip of another parked aircraft, EC-CSX. After this impact, the EC-GOZ slowed enough for the pilot to reach it, board, and stop the engine by turning the magneto switch to OFF, closing the throttle, and setting the mixture to idle cut-off.
Post-Accident Inspection
After the accident, an inspection of the aircraft revealed that the parking brake functioned correctly and could hold the aircraft; however, it was noted that on this type of aircraft, the parking brake is typically unable to hold the aircraft at high engine power, and it may release once the aircraft begins moving even if properly applied. The magneto switch worked correctly and grounded the magnetos in the OFF position.
Analysis and Conclusion
Because the engine started normally and no evidence of a system failure was found, it is inferred that the magneto switch was in one of the ON positions (1, 2, or BOTH). The damage to the parked aircraft suggests the engine was producing significant power, implying the throttle was advanced beyond 1/4. The rapid acceleration and proper parking brake function indicate that the parking brake was either not set or released when the aircraft moved. The engine was primed, the magneto switch was on, the throttle was at 1/4 or more, and the mixture was rich, making a start likely when the propeller was turned. The pilot stated he intended only to rotate the propeller to aid subsequent starting with external power, but the actions were essentially the same as a manual start. The pilot had limited experience and had not flown for some time, which may have contributed to improper procedures and omission of basic checks. The most probable cause of the accident was performing a manual engine start without taking the necessary precautions.