What happened
The aircraft was loaded with 100 gallons of 2-4-D herbicide and 40 gallons of fuel. During the preflight run-up check, the pilot observed a magneto drop of 225 RPM. He stated that leaning the fuel mixture cleared the excessive decrease in RPM, allowing him to observe 2500 RPM on the engine tachometer during the takeoff roll. The pilot reported that the aircraft did not seem to want to gain speed as expected, rolling approximately 2700 feet before lift-off. After leaving the ground, the aircraft failed to gain speed while climbing to about 75 feet AGL. The engine popped and sputtered as the plane settled. During a landing in a soft field, the aircraft nosed over, soaking the pilot with the 2-4-D chemical load.
The investigation
An examination and operational check of the engine revealed no precrash malfunction or failure. Takeoff performance data indicated that the aircraft should have been able to clear a 50-foot obstacle in 1350 feet. The density altitude at the time was about 6500 ft MSL. The pilot noted he would have dumped his load if he had more time.
Findings
The excessive takeoff roll and poor climb performance were attributed to the high density altitude and the heavy cargo load. The engine functioned normally during the operational check.