Incident Description
A private pilot and a flight instructor were conducting a dual instrument instructional flight. According to their statements, the takeoff roll progressed normally until the airplane had traveled approximately one-third of the runway length. At that point, they observed that the airspeed indicator showed zero. They responded by reducing the throttle and applying the brakes. Despite these actions, the airplane continued past the departure end of the 3,200-foot runway. It then ascended an embankment and came to rest in an adjacent corn field.
Witness Account
A witness reported that the pilots applied the brakes while maintaining full engine power for about 1,000 feet. He stated that he heard the pilots reduce throttle when the airplane neared the runway end. The witness estimated the airplane's speed at 40 mph when it departed the runway surface.
Postaccident Findings
Examination of the airplane after the accident revealed that a mud dauber nest was obstructing the pitot tube. The blockage likely prevented the airspeed indicator from functioning correctly during the takeoff roll.