Varga Aircraft Corp. 2150A N4635V accident near Bowling Green, Ohio

Probable cause

The pilot's loss of control due to impairment from carbon monoxide poisoning. Contributing to the accident was the corrosion of the heat exchanger and the failure of maintenance personnel to adequately inspect and repair or replace the exchanger during the most recent annual inspection.

NTSB analysis

The private pilot was performing a visual flight rules cross-country flight after purchasing the airplane. After flying for about 1 hr 20 minutes, the airplane suddenly entered a spiraling descent from cruise flight. Witnesses observed the airplane flying erratically at low altitude before it impacted an open field; they stated that the engine was running until impact.

Toxicological testing of specimens taken from the pilot found 55% carbon monoxide saturation of blood. At carbon monoxide levels above 40%, people typically experience incapacitating symptoms such as severe confusion, agitation, seizures, loss of consciousness, and death.

Examination of the airplane's heat exchanger showed that the outside casing had either previously been repaired or had been originally constructed of metals with different properties. About one-half of the casing was discolored and exhibited varying signs of corrosion (the other half did not). Small holes were found where corrosion had occurred in the casing material. The holes from the corrosion provided a means for carbon monoxide to enter the cockpit from the exhaust system.

Federal guidelines for annual aircraft inspections require an inspection of the exhaust systems for cracks, defects, and improper attachment during each 100-hour or annual aircraft inspection. Maintenance logbooks indicated that the airplane's most recent annual inspection was completed less than 1 month before the accident. The available maintenance logbooks did not contain any record of repairs or replacement of the heat exchanger. However, the condition of the heat exchanger is indicative of an insufficient annual inspection that did not detect and correct the corroded heat exchanger.

It is likely that impairment caused by acute carbon monoxide poisoning led to the pilot's loss of airplane control. The corrosion in the heat exchanger allowed carbon monoxide to enter the cabin.

Text from the NTSB. Open the NTSB docket for CEN17FA207 for the full record.