What happened
The accident occurred during a training flight involving an instructor and a student pilot. The student attempted a landing but established the aircraft in an improper attitude. Following the balked landing, the instructor assumed control of the aircraft and initiated a go-around procedure.
During the initial phase of the go-around, both engines failed to respond when the throttles were advanced. Both engines subsequently decelerated, causing the airspeed to decrease. The crew retracted the flaps, which resulted in a reduction of hydraulic pressure. Unable to maintain minimum control speed (VMC), the instructor lost control of the aircraft. The aircraft crashed and was destroyed by a post-crash fire. Damage was also sustained to the airfield perimeter fence.
The investigation
Post-accident teardown and testing of the engines revealed significant mechanical issues. There was a heavy accumulation of oil and tar residues on the bleed valves and throughout the compressors of both engine number 1 and engine number 2. This contamination limited the ability of the engines to respond to throttle movement.
Maintenance records indicated a history of recent engine and propeller oil leaks. Although maintenance procedures required engine washes after such leaks, there was no record that these washes had been performed.
Findings
The primary factor in this accident was the failure of both engines to respond to throttle inputs during the go-around. This failure was directly caused by the heavy accumulation of oil and tar residues on the bleed valves and throughout the engine compressors. The lack of required maintenance, specifically engine washes following known oil leaks, contributed to the condition that prevented proper engine operation.