What happened
On 20 January 2020, a Grumman G-164A agricultural aircraft, registration ZS-IRW, was conducting crop-spraying operations near the Doornkop area. After successfully completing two spraying passes, the pilot returned to Middelburg Aerodrome (FAMB) to uplift a third load of chemicals.
Upon departing for the final pass, the aircraft was climbing at approximately 50 feet above ground level when the engine lost power and ceased operation. The pilot immediately jettisoned the remaining chemical payload to reduce the aircraft's weight and executed an emergency landing in an open field. The aircraft struck soft, muddy terrain, causing the main landing gear to snag. This resulted in the aircraft rolling and flipping into an inverted position. While the aircraft sustained substantial damage, the pilot escaped without injury.
The investigation
An investigation by the SACAA AIID examined the mechanical state of the Pratt & Whitney R1340-AN1 engine. The engine had been in service for 555.4 hours since its last overhaul, which had taken place in May 2001. Investigators performed a teardown inspection of the engine at a specialized facility in Springs. The inspection of the rear engine case revealed significant internal damage, specifically involving the supercharger components.
Findings
- The primary cause of the engine failure was a failed impeller bearing and broken impeller gear, which led to a malfunction of the supercharger.
- The aircraft was operating in an agricultural capacity (Part 137) under Visual Flight Rules (VFR).
- The engine had not undergone a full overhaul in approximately 18 years, as the manufacturer's recommended interval is based on flight hours rather than a specific time limit.
Safety action
- It is recommended that the engine manufacturer implement a specific time limit for overhauls to ensure safety standards are maintained for aircraft that fly fewer hours per year.