What happened
On June 20, 1988, at approximately 12:00 hours, a Grumman G-164A agricultural aircraft, registration CS-AQK, was performing chemical weeding operations over a rice field near Herdade da Comporta. The aircraft, operated by SANAGRI, was executing its eleventh flight of the day.
As the pilot completed a pass and began to pull up, a loud bang was heard from the engine, followed by a sudden loss of power and intense vibrations. The pilot initiated an emergency landing in the rice field. Upon touchdown, the aircraft struck a small earthen berm, causing the plane to capsize. The pilot, an experienced commercial pilot with 8,000 total flight hours, escaped the wreckage without injury, but the aircraft was destroyed.
The investigation
The GPIAAF investigation focused on determining whether the power loss was caused by an engine failure or an external impact. Investigators examined the engine and noted that while the propeller blades were damaged, the engine still showed apparent compression during a spark plug inspection.
Two primary hypotheses were considered. The first was a propeller strike against the ground; such an impact could bend the propeller and cause the observed vibrations and power loss. However, no clear evidence of a strike was found, and a ground marker (swatter) present at the site did not observe any contact. The second hypothesis was an internal engine failure. While a full engine test bench analysis was deemed impractical due to the extent of the aircraft's destruction, the investigation could not definitively rule out an engine malfunction.
Findings
- The aircraft was fully certified, maintained, and airworthy at the time of the accident.
- The pilot was highly qualified, possessing significant experience in agricultural flight operations.
- The primary cause of the accident was either a propeller strike with the ground or an unidentified engine failure.