On September 1, 2014, about 1050 eastern daylight time, a Cessna 180, N6510A, was substantially damaged when it impacted trees and terrain during the initial climb after takeoff from Hampton Airfield (7B3), North Hampton, New Hampshire. The airline transport pilot and a passenger were fatally injured. Visual meteorological conditions prevailed, and no flight plan was filed for the Part 91 personal flight, destined for a private airport in Kingston, New Hampshire. On the day of the accident, the airport was hosting its annual customer appreciation day.

According to witness statements and video images, the pilot contacted the airport advisory frequency from a position approximately 5 miles west of 7B3. The airplane then overflew the south end of the airport and the pilot advised that he would be joining the downwind leg of the traffic pattern for "Runway 22." The pilot then advised that he was joining the base leg of the traffic pattern, and then reported that he was "landing south" without indicating the runway number.

The airplane landed normally and shut down at the fuel pumps at 1023. The pilot then refueled the airplane with approximately 31 gallons of 100 LL aviation gasoline, finishing at approximately 1036.

After starting the airplane and taxiing away from the fuel pumps, a witness observed a seat belt hanging out of the passenger door. The witness gained the pilot's attention and advised him about the seatbelt. The pilot then taxied to runway 02. Witnesses did not observe the pilot perform a runup prior to turning onto the runway, and also noted that the flaps were partially extended before the takeoff roll began.

The airplane appeared to take off normally with the tailwheel coming off the surface of the runway first, followed by the main landing gear wheels. The ground run was approximately 890 feet. After liftoff, the airplane's angle of attack (AOA) began to increase. One witness stated that as the AOA began to increase, the pilot's left hand reached for the glareshield, while another witness observed the pilot's left hand already on the glareshield as the AOA began to increase.

Approximately 320 feet later, the airplane's AOA was still increasing and the airplane's altitude was higher than a group of approximately 73' tall trees adjacent to the west side of the runway. Moments later, the airplane rolled and yawed to the left, its AOA decreased through a level flight attitude, to a steep nose down attitude, engine RPM decreased "as if it was being throttled back to idle" and the airplane went out of view behind trees. The sound of impact was then heard.

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

The pilot had reported to the FAA that he had hypertension, gastroesophageal reflux disease (GERD), and high cholesterol. However it is unlikely that either of these conditions or associated medications contributed to the accident.

Postaccident toxicology testing of the pilot's specimens identified levels of diphenhydramine, a sedating antihistamine, indicating it 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 a driving simulator study, a single dose of diphenhydramine impaired driving ability more than a blood alcohol concentration of 0.1%. 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, a shortacting sedative hypnotic used as a sleep aid, however it is not likely that the passenger was significantly impaired by zolpidem at the time of the accident.

Based on the pilot's reported hand position at takeoff, it is possible that he had decided to let his 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 decisionmaking or affected his ability to respond to the stall quickly.

The NTSB determined that probable cause of this accident was 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.