2005 Grumman G-164A Super Ag-Cat accident near Palma del Río (EC-CZC)

Accident overview and flight details On 18 April 2005, a Grumman G-164A Super Ag-Cat with registration EC-CZC, operated by FAASA Aviación (Fumigación Aérea Andaluza, S. A.), crashed near the aerodrome of Palma del Río in Córdoba, Spain. The aircraft was on a private general-aviation familiarization flight. At 11:00 local time, the pilot took off from runway 25. During the initial climb, the pilot observed that the engine was beginning to fail and elected to make an emergency landing in a field located 700 m from the runway. After a right turn and touchdown, the aircraft traveled 17 m over the ground before overturning. The pilot was able to leave the aircraft under his own power and was not injured. Two mechanics on duty at the aerodrome witnessed the event and reported that the takeoff had been normal; after the turn, they heard a series of explosions accompanied by black smoke followed by white smoke until impact. ## Aircraft, engine, and maintenance data The accident aircraft was a 1974-built Grumman Ag-Cat G-164, a biplane with fixed tail-dragger landing gear, primarily used for agricultural work. It was powered by a single Pratt & Whitney R-1340-AN-1 nine-cylinder radial engine, serial number 14522, rated at 600 hp. On the day of the accident, the aircraft had a total of 2,342:30 flight hours, and the engine had 7,088:20 hours. The engine had been installed in February 1998 with 00:00 hours since overhaul, at which time the aircraft had 1,454:10 hours and the engine had 6,200 hours since manufacture. ## Pilot and operational context The pilot in command was 35 years old and held a commercial pilot license for airplanes. He had 500 total flight hours and 10 hours on type. Although his type experience was limited, he had flown other tail-dragger aircraft. The flight was a familiarization flight because the pilot intended to acquire an aircraft of this type. ## Meteorological and aerodrome information Weather conditions were suitable for the planned flight. The temperature was 15 °C, visibility was more than 10 km, and the wind was about 10 kt from 250° without gusts. The aerodrome of Palma del Río is in the province of Córdoba and has an asphalt runway oriented 07/25. ## Wreckage and impact findings The aircraft sustained substantial damage. The main landing gear and the spar acting as its support were broken. The tail skid showed no deformation. During the overturn, the upper wing came to rest on the ground and moved forward. The tail assembly suffered significant deformation in both the horizontal and vertical stabilizers. These deformations prevented deformation of the cockpit, which helped the pilot avoid injury. Both propeller blades were bent backward. One blade showed no damage or scratches. The other had a small leading-edge deformation and light scratches on the upper and lower surfaces. ## Investigation and technical findings Inspection of the flight and engine control systems showed no abnormalities other than those caused by impact deformation. The cockpit was in good condition, with no broken instruments. Engine instruments read “0,” except the manifold pressure gauge, whose needle was stuck at 32 inches of mercury. All fuel, located in the upper wing, spilled onto the ground, making it impossible to obtain samples to test for water in the tanks. The mechanics reported that the tanks had been drained with satisfactory results. In the engine inspection, the rocker shaft for the exhaust valve of cylinder No. 2 was missing. The valve was closed, and the rocker could move in any direction. No abnormality was found in the exhaust valve closing spring for that cylinder. No part of the rocker shaft was recovered. Inside the intake tube of cylinder No. 2, combustion residues, soot, and carbon were observed. The front spark plugs of all cylinders showed signs of irregular combustion, especially cylinders 4 and 6, which had small round greenish deposits. ## Analysis and probable cause In radial engines, intake and exhaust valves are located on the outside of the cylinders and are closed by springs that must be compressed to open them. The force compressing the springs is transmitted from a cam plate in the crankcase through a pushrod to one end of a rocker in the cylinder head. The rocker acts as a lever pivoting on its shaft. If the rocker loses its pivot, it can no longer transmit the force needed to compress the spring and open the valve. In cylinder No. 2, once the exhaust-valve rocker shaft failed, the rocker could no longer open the valve, leaving it permanently closed. Combustion gases remained in the cylinder at very high temperature. The presence of combustion residues, soot, and carbon in the intake tube of cylinder No. 2 indicated that when the intake valve opened, hot gases from the cylinder exited through the intake port and manifold, raising the temperature of the mixture feeding the cylinders. The greenish deposits on the spark plugs indicated copper from the central electrode beginning to melt due to very high temperatures inside the cylinders. The signs of poor combustion were caused by very hot mixture and exhaust-gas residues, producing irregular engine operation, explosions in the exhaust and intake passages, smoke emission, and a significant loss of power leading to engine stoppage. The propeller-blade damage supported this: both blades were bent backward with no material loss at the tips, indicating they touched the ground at very low speed and without power. The blade with the more extreme bend and damage likely touched the ground first, while the other was the one over which the aircraft overturned. The probable cause of the accident was an engine failure caused by the fracture and loss of the rocker shaft for the exhaust valve of cylinder No. 2. The reasons for the fracture of the rocker shaft could not be determined because no piece of the component was found for metallographic analysis.