Amateur-built HUMMEL BIRD N9001N accident near Defuniak Springs, Florida

Probable cause

The pilot's failure to maintain airplane control due to the airplane’s exceedence of its maximum gross weight and center of gravity’s most rearward limit and his lack of familiarity with the airplane make and model, which resulted in an aerodynamic stall and subsequent spin. Contributing to the accident was the pilot's decision to knowingly operate the airplane over the maximum allowable gross weight with reduced longitudinal stability.

NTSB analysis

Witnesses reported observing the airplane porpoising along its longitudinal axis during its climb after takeoff. About 300 feet above ground level, the airplane pitched up to a nose-high attitude and rolled to the right; it subsequently impacted the ground in a right-wing-low, nose-down attitude. Postaccident examination did not reveal any preimpact mechanical malfunctions or abnormalities that would have precluded normal operation. However, the weight of the airplane (not including fuel) plus the weight of the pilot exceeded the airplane's maximum gross takeoff weight and the center of gravity (CG) was aft of the most rearward limit. Although any fuel would have moved the CG forward of the most rearward limit, it also would have increased the airplane's takeoff weight. The pilot reported to his aviation medical examiner (AME) that the airplane was having "great" difficulty with longitudinal stability. He also noted that his weight gain caused the airplane to be "over gross," most likely causing the control problems. The AME advised the pilot to stop flying the airplane.

Because the airplane was at or aft of the rear CG limit, it would have been very sensitive in pitch control and may even have been at or near a dynamically unstable flight regime in terms of pitch handling. Accordingly, the airplane would have required more nose-down trim adjustment. Additionally, because stall speeds increase as gross weight increases, the airplane would have stalled at a higher airspeed. Therefore, it is likely that, during the climb, the airplane stalled at a higher airspeed than the pilot would have expected due to its exceedence of the maximum gross weight and that it subsequently entered a spin.

A review of the pilot's logbook indicated that he had accumulated only 4.4 flight hours in the 2 years preceding the accident flight with only 0.3 hour in the accident airplane. It is likely that the pilot's lack of experience in the airplane make and model contributed to his decision to take off with the airplane in an overweight condition and his inability to understand the seriousness of the situation. Although the postmortem toxicology testing was positive for three drugs used in the treatment of hypertension, none of the medications should have been impairing and were unlikely to have contributed to the accident.

Text from the NTSB. Open the NTSB docket for ERA12FA326 for the full record.