History of Flight
On July 21, 2019, about 0705 eastern daylight time, an Ayres S2R-G10 airplane, registration N766BF, was substantially damaged during an accident near Breckenridge, Michigan. The pilot, who was the sole occupant, was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 137 as an agricultural application operation.
The pilot reported that the accident occurred during his second flight of the day; the first flight had been uneventful. Before departure, the airplane was loaded with approximately 60 gallons of Jet-A fuel and 325 gallons of a fungicide and water mixture in the hopper. Shortly after takeoff from runway 27, at about 100 feet above ground level, the pilot observed a sudden increase in exhaust gas temperature (EGT) exceeding the engine's limit. He immediately reduced throttle, but the engine experienced a total loss of power. The pilot activated the igniters in an attempt to restart the engine, but due to low altitude, he was forced to execute an emergency landing in a cornfield. He lowered the flaps and leveled the wings. Upon contact with the corn, the main landing gear collapsed. After landing, the pilot activated the emergency fuel cutoff and turned off the igniters, generator, and battery.
Data from the airplane's engine monitor revealed a sudden and complete loss of engine oil pressure shortly after takeoff. This resulted in an inability to control propeller blade angle, accompanied by a decrease in engine speed and a rise in EGT. The EGT increased from 535°C to 850°C within 10 seconds following the loss of oil pressure. After the accident, the engine N1 stabilized at about 44% for roughly 5 seconds until fuel flow and fuel pressure simultaneously dropped to zero, consistent with the pilot closing the emergency fuel shutoff valve.
Aircraft Information
The engine, a Honeywell TPE-331-10-511M (serial number P42076C), had undergone a 100-hour inspection on July 19, 2019, at which time it had accumulated 16,857.5 hours since new and 603.9 hours since its last overhaul. After the inspection, the airplane accrued an additional 2 engine starts, 4 landings, and 1.74 flight hours.
According to maintenance records, the engine oil cooler was replaced during the 100-hour inspection. The oil cooler is mounted remotely below and aft of the engine in the nacelle, where it receives ambient airflow for heat transfer. Flexible hoses carry hot engine oil from the engine scavenge pump to the oil cooler and return cooled oil to the engine oil tank.
Wreckage and Impact Information
A Federal Aviation Administration (FAA) airworthiness inspector documented the accident site on the day of the accident. The airplane was found upright in a cornfield approximately 1,400 feet from the runway end. The impact path through the corn was 70 feet long on a magnetic heading of 200°. No fire was observed. The fuselage, cockpit, and empennage remained intact. Both wings were attached to the fuselage but sustained impact damage to leading edges and skins. The flaps were fully extended. Both main landing gear had collapsed during impact. Flight control continuity was confirmed from the cockpit to all control surfaces. Engine and propeller control continuity was also established. The upper half of the hopper was undamaged, but the hopper gate and spray equipment were damaged by ground impact. All four propeller blades remained attached to the hub, bent aft around the engine cowl with minor chordwise scratching.
The FAA inspector reported that the mechanic who had replaced the oil cooler two days earlier assisted at the site. The mechanic stated that oil was still present in the tank after the accident, but the inspector did not personally verify this. Several weeks later, when the engine was separated from the airframe, the oil tank contained no oil. The tank had dents and scratches consistent with impact but was not breached. The oil cooler transfer hoses and fittings were found intact and tight.
Engine Examination
Disassembly of the engine at the manufacturer's facility revealed no evidence of mechanical malfunction or failure that would have prevented normal operation. Normal oil wetting and wear signatures were present throughout. No internal oil leak was found, but oil was observed on external surfaces of several engine accessories. The oil on external surfaces did not originate from the engine case, accessories, or reduction gearbox.
Examination of on-scene photographs taken by the FAA inspector showed engine oil on several components inside the engine nacelle, including the engine rear frame, exhaust duct, firewall/battery box, oil cooler just below the exhaust duct, and the oil cooler transfer hoses. Oil was pooled on the battery box frame ledge, consistent with escaped oil being distributed inside the nacelle. Oil wetting extended to the top of the exhaust duct and engine rear frame, consistent with eductor operation at high engine speed. Additional oil wetting was observed on the center of the engine exhaust pipe at the same plane as the oil cooler, becoming less apparent near the midpoint of the rear frame. The internal surface of the eductor mixing duct was oil-wetted, consistent with engine exhaust drawing escaped oil particles from the nacelle through the annulus and into the mixer duct. The fuel control unit and fuel pump cases were also oil-wetted.
The airframe portion of the engine oil system—including the oil cooler and two transfer flex-hoses—was examined to identify the oil leak source. Visual inspection of the oil cooler revealed a weld fracture along the edge of the cooler housing and a deformed mounting flange. The fracture appearance and location were consistent with impact damage. The fracture was cleaned, welded closed, and pressure tested while submerged; no leaks were detected, confirming the cooler's integrity. The two transfer flex-hoses also showed no leaks during pressure testing.