DEN08FA155 · Cessna 172L

The flight instructor and student pilot were planning to do touch-and-go landings. A witness reported that the airplane took off on Runway 17, climbed about 100 feet, and then nosed down. The weather was clear and the wind was nearly straight down the runway. The flight instructor had logged nearly 3,000 hours of total flight time, with over 600 hours instruction and over 600 hours in the Cessna 172. Examination of the aircraft revealed no evidence of a preimpact mechanical malfunction. The flight instructor had a long history of diabetes, and had recently started a new injectable medication (exenatide, 10 micrograms twice a day) to help control his blood sugar. This medication can result in impairment due to low blood sugar, but he had not reported any adverse effects, and he was observed to be behaving normally the day prior to and the day of the accident. He was at extremely high risk of obstructive sleep apnea given his height (70 inches), weight (285 pounds), and poorly controlled blood pressure. Obstructive sleep apnea often results in impairment, but he was apparently not observed to snore while sleeping, a hallmark of the condition. Autopsy revealed an enlarged heart (it weighed 500 grams), but it was not thickened, suggesting an apparently unrecognized heart condition, dilated cardiomyopathy, that can result in sudden incapacitation. Given the failure of this experienced instructor pilot to either execute a normal climbout or appropriately oversee the climbout by his novice student, it is possible that he was incapacitated by a cardiac event. It is also possible, though less likely, that he was impaired either by unrecognized low blood sugar as a result of his new diabetes medication or by fatigue from unrecognized obstructive sleep apnea. However, the investigation could not conclusively determine if the instructor was impaired at the time of the accident.

Verbatim NTSB analysis and probable cause from the NTSB dataset