NTSB Factual Report

October 20, 2016, about 1350 central daylight time (CDT), the pilot of a Zenith CH-750, N8681, made a forced landing in a field 3 miles northwest of Morristown, Minnesota, after the engine lost power. The pilot, the sole occupant on board, was seriously injured. The airplane was substantially damaged. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations (CFR) Part 91 as a personal flight. Visual meteorological conditions (VMC) prevailed at the time of the accident, and no flight plan had been filed. The local flight originated from a private airstrip in Morristown about 1340.

The following is based on two interviews between Federal Aviation Administration (FAA) inspectors and the pilot. The pilot said he had fueled the airplane that morning with 82-octane automotive fuel that he had recently purchased from a service station. He started the engine and allowed it to warm up but had to shut the engine down when he was called away. He returned about an hour later, started the engine, and took off. When he reached an altitude of about 100 feet AGL, the engine lost power. He turned the electric fuel pump on. The engine restarted momentarily but failed to keep running. He did not remember if he turned the fuel selector valve to the opposite tank. After maneuvering to avoid cattle and a tree, the airplane touched down on its main landing gear. Due to the steepness of the hill and the grass, the airplane came to an abrupt halt. Examination of the airplane revealed the nose gear had collapsed, the fuselage was buckled, and the engine was knocked askew to the right. The left wing had separated from the fuselage and bore leading edge crushing. When asked what he thought may have happened, the pilot said he felt it was a vapor lock due to the time between the first and second engine starts and takeoff. He also stated that the engine had a safety feature that prevented it from starting if the throttle was out of the idle position. He felt that he could have gotten the engine running if he had brought the throttle back to idle but he failed to do so during the emergency.

On October 28, 2016, the airplane and engine were examined at Wentworth Aircraft in Lakeville, Minnesota, under the auspices of a Federal Aviation Administration (FAA) inspector. Recovered fuel was yellow in color and had the aroma of "aged" automobile fuel. The top spark plugs were removed and examined. They appeared old and corroded at the electrode ends. The electrode gaps were not consistent. The number 3 plug appeared had a substantial gap, and the number 1 plug had a narrow gap. These were the only mechanical anomalies noted. It was also determined the airplane did not have a fuel vapor line installed.

A Rotax Aircraft Engines flight safety representative verified a vapor lock was a possibility, especially since the owner had not installed a fuel vapor return line and old automotive fuel was found in the fuel system. He stated that the condition and corrosion of the spark plugs and the spacing of the electrode gaps could also affect engine performance. He also stated the engine did not have a safety device installed that would prevent it from starting when the throttle was in other than the idle position.

Examination of the maintenance records revealed the pilot had complied with Service Bulletin SB-912-053-UL on May 24, 2007, mandating the replacement of the fuel pump. However, there was no record that he had complied with SB-912-063-UL that mandated replacing the 5-year life-limit fuel pump.

NTSB Probable Cause

A total loss of engine power due to fuel vapor lock. Contributing to the loss of engine power were the corrosion of the spark plugs and the spacing of the electrode gaps.