Cessna 180 N6510A accident near North Hampton, New Hampshire

Probable cause

The pilot’s failure to ensure the airplane maintained adequate airspeed during the initial climb and the subsequent exceedance of its critical angle of attack, which resulted in an aerodynamic stall. Contributing to the accident were the pilot’s impairment due to a sedating antihistamine, which led to his decision to possibly allow the passenger to attempt the takeoff, and his delayed remedial action to lower the nose when the airplane began to pitch up too much.

NTSB analysis

Witnesses reported observing the commercial pilot and passenger departing from the turf runway. After a normal takeoff, the airplane's angle of attack (AOA) began to increase, and it continued to increase until the airplane's critical AOA was exceeded. The airplane then experienced an aerodynamic stall and entered an uncontrolled descent.

Postaccident examination of the airplane, including the flight controls and stall warning system, and the engine revealed no evidence of any preaccident mechanical failures or malfunctions that would have precluded normal operation.

The pilot had reported that he had hypertension, gastro-esophageal reflux disease (GERD), and high cholesterol and that he was using lisinopril, pantoprazole, and simvastatin to treat those conditions to the Federal Aviation Administration. However, given that high blood pressure and high cholesterol cause no direct symptoms and that no evidence of a stroke, heart attack, or significant natural disease were identified on autopsy, it is unlikely that either of these conditions or the medications the pilot was taking to treat them contributed to the accident. Further, although GERD can cause heartburn, it is unlikely to have been acute or severe enough to have contributed to the accident.

Postaccident toxicology testing of the pilot's specimens identified significant levels of diphenhydramine, which is a sedating antihistamine, in the femoral and cavity blood, indicating that it is likely that the pilot's diphenhydramine level was near the middle of the therapeutic window at the time of the accident. Even at therapeutic levels, diphenhydramine is quite impairing. In fact, in a driving simulator study, a single dose of diphenhydramine impaired driving ability more than a blood alcohol concentration of 0.100%. Thus, it is very likely that the pilot was impaired by diphenhydramine at the time of the accident.

Toxicology testing of the passenger's specimens detected a level of zolpidem, which is a short-acting sedative hypnotic used as a sleep aid, in the heart blood that was at the lower end of the therapeutic window and would likely have been significantly lower at the time of the accident. Although it could not be determined with certainty, it is not likely that the passenger was significantly impaired by zolpidem at the time of the accident.

The pilot was seated in the left seat; one witness reported seeing his left hand on the glareshield as the AOA began to increase whereas another witness reported seeing his hand reach for the glareshield as the AOA began to increase. Based on the pilot's reported hand position at takeoff, it is possible that he had decided to let the unrated passenger attempt the takeoff; however, this could not be definitively determined. In either case (with the passenger or the pilot flying), the pilot failed to ensure that the airplane maintained adequate airspeed, which led to the airplane exceeding its critical angle of attack. It is likely that the pilot's impairment by diphenhydramine contributed to the accident and led to his poor decision-making or affected his ability to respond to the stall quickly.

Text from the NTSB. Open the NTSB docket for ERA14FA417 for the full record.