CEN23FA258 · Cessna 177

The private pilot and the passenger were conducting a personal cross-country flight in the airplane that the pilot recently purchased. The pilot did not have previous flight experience in the airplane make/model before he took possession of the airplane the day before the accident. According to the passenger, the airplane had full fuel tanks (48 gallons usable) before the previous flight leg. Based on available flight track data, the previous flight leg was at least 2.9 hours in duration. The passenger reported that after the previous flight leg, the right fuel gauge indicated “empty” and the left fuel gauge indicated “1/4” tank remaining.

Before the accident flight, the pilot was unable to dispense fuel from the self-serve fuel pump and so believed that there was no fuel available at the airport. However, the airport manager, who was not present at the time, stated that the self-serve fuel pump operated normally and there was fuel available when he tested it after the accident. According to the passenger, the pilot decided that the airplane had enough fuel for the flight.

Based on ADS-B flight track data and recorded voice transmissions, about 38 minutes into the flight the airplane was about 5.3 statute miles (sm) from the intended destination airport when the pilot transmitted that the airplane was “low on fuel.” Then, about 2 minutes 20 seconds later, the pilot transmitted “…engine out, coming in runway five, engine out.” At that time, the airplane was about 1.8 sm west-southwest of runway 5 and about 600 ft above the runway threshold elevation.

Airplane performance calculations using ADS-B flight track data revealed that the pilot did not establish and maintain best glide speed after the loss of engine power; the airplane was 15-20 mph below best glide speed. However, based on the airplane’s expected glide ratio (10:1) at best glide speed, it is unlikely the airplane had enough altitude remaining to safely reach the runway even if the pilot maintained best glide speed. The final ADS-B track point placed the airplane about 0.8 sm from the runway threshold, about 200 ft above ground level (agl), at a calibrated airspeed of about 61 mph, and a descent rate of 450 feet per minute (fpm).

According to the passenger, the pilot was unable to restore engine power and intended to land on the lake to avoid the trees and houses that surrounded the lake. However, while above the lake, the airplane “stalled” as it descended through tree-top height. The aerodynamic stall resulted in the airplane’s nose dropping almost straight down. The airplane immediately started to sink after it impacted the lake. The passenger recalled remaining conscious but unable to see anything in the murky green water. Believing that she would drown, she instinctively unfastened her seat belt and swam to the surface. The pilot did not emerge from the submerged airplane. After the accident, the passenger told at least one individual who provided her assistance that the airplane ran out of fuel while on approach to the airport.

The airplane sustained substantial damage to the fuselage and both wings. Examination of the wreckage did not reveal any evidence of a mechanical malfunction of the airplane or its engine. However, several engine components exhibited signatures consistent with an excessively rich air-to-fuel ratio. The passenger reported that the pilot had difficulty leaning the engine and, specifically, that the engine would begin “stumbling” after the mixture control was pulled 1.5 to 2 inches aft of full rich. The engine “stumbling” as described by the passenger when the mixture was adjusted was consistent with an excessively lean air-to-fuel mixture.

Therefore, based on the available evidence, it is likely the pilot did not properly lean the air-to-fuel mixture during the accident flight. Consequently, the fuel consumption rate during the flight was greater than he might have anticipated. Based on the fuel quantity gauge indications reported by the passenger, the airplane had about 6 gallons of fuel available before the accident flight. According to the airplane owner’s manual, the engine, operated at 75% brake horsepower with a properly leaned air-to-fuel mixture, would result in a fuel consumption rate of 8 to 8.5 gallons per hour (gph). Operated as such, the estimated 6 gallons of fuel would have provided 42-45 minutes of flight time with a properly leaned engine. The loss of engine power occurred at least 40 minutes into the flight (that is, not including the time associated with the engine startup, taxi, takeoff).

Based on the available information, it is possible the airplane had enough fuel at departure to reach the intended destination airport if the pilot had properly leaned the engine during the flight. Additionally, the minimal distance remaining to the intended destination airport (1.8 sm) when the loss of engine power occurred further supports that the airplane might have departed with enough fuel to reach the airport. However, it is unlikely the airplane departed with the additional 30 minutes of fuel reserve required by fuel-planning regulations for day visual flight rules flights. The pilot’s decision to depart with barely enough fuel to make the flight under ideal operating conditions resulted in fuel exhaustion and total loss of engine power at the end of the flight.

Toxicology results indicate that the pilot had used a delta-8-THC product. Delta-8-THC has psychoactive and intoxicating effects that can impair motor coordination, reaction time, decision making, problem solving, and vigilance. However, the precise timing of the pilot’s last cannabis use, and whether it was causing significant impairing effects at the time of the accident, could not be determined from the measured levels of delta-8-THC and its metabolites. However, products containing Delta-8 THC have not been evaluated or approved by the Food and Drug Administration for safe use in any context.

Toxicology results also indicated that the pilot had used diphenhydramine. The measured diphenhydramine level in blood would be above the typical therapeutic range had it been measured in a living person. However, interpretation of postmortem diphenhydramine levels is complicated by the drug’s significant potential for postmortem redistribution. Regardless, the measured level of diphenhydramine was from the pilot’s peripheral blood, which is the preferred postmortem blood specimen type. Overall, the diphenhydramine level in postmortem peripheral blood indicates that the pilot likely was experiencing impairing effects of his use of diphenhydramine, but the specifics of impairment could not be determined from the measured levels alone. Diphenhydramine may cause cognitive and psychomotor slowing and drowsiness. The FAA recommends a 60-hour waiting period from the last dose of diphenhydramine to piloting an aircraft to allow sufficient time for the drug to be cleared from circulation.

Toxicology results also revealed the pilot used the prescription antidepressant medication fluoxetine. The pilot did not report the use of fluoxetine when he applied for his last aviation medical examination, completed more than 11 years before the accident, and the reason for its use is not documented. It is possible that fluoxetine and/or the underlying condition for which it was being used may have had some performance-impairing effects. However, no more-specific conclusions about impairment can be drawn from the reviewed medical evidence.

Based on the pilot’s improper preflight fuel planning and decision-making, inflight fuel mismanagement, and failure to maintain adequate airspeed and control of the airplane during the forced landing, it is likely he was experiencing impairing effects from the detected substances.

Verbatim NTSB analysis and probable cause from the NTSB dataset