What happened
Following the completion of a local banner-tow mission and the successful release of the banner, the pilot was maneuvering for landing in a Piper PA-25. During this maneuver, the aircraft stalled at a low altitude. The airplane impacted flat terrain on airport property, resulting in substantial damage to the aircraft. The certificated commercial pilot sustained serious injuries during the accident. At the time of the event, weather conditions were visual meteorological conditions with reported winds of 9 knots.
The investigation
The investigation focused on the aircraft's stall warning system, which utilized a vane-activated switch on the wing and a cockpit light. Electrical continuity testing and x-ray examination of the switch determined that the internal contacts were fused, preventing the switch from operating as designed. Analysis by the Safety Board's Materials Laboratory confirmed that the stall warning light was not illuminated at the time of impact. Additionally, calibration testing of the airspeed indicator showed that the instrument read approximately 8 mph high at speeds up to at least 90 mph.
Findings
- The internal contacts of the wing vane-activated switch were fused, rendering the stall warning system non-functional.
- The airspeed indicator provided inaccurate readings, specifically reading approximately 8 mph high during speeds up to 90 mph.