What happened
On January 11, 2016, a Cessna 150H, registration OB-2073, was conducting a scheduled training flight from Pisco Airport to the Lib Mandi aerodrome. The flight, operated by a flight school, included an instructor and a student pilot. After successfully completing landing and takeoff maneuvers at Lib Mandi, the crew began the return flight to Pisco.
Approximately 15 minutes into the return leg, the crew detected smoke and a burning odor originating from the left side of the engine, followed by a loud explosion. The engine power dropped significantly to approximately 1,500 rpm. The instructor took control of the aircraft and declared an emergency, intending to perform a forced landing on a nearby beach. At a safe altitude of 500 feet, the pilot shut down the engine. During the landing on the sandy terrain, the nose gear sank into the sand, causing the aircraft to overturn and come to rest in an inverted position.
The investigation
The investigation focused on the mechanical failure of the engine and the subsequent landing dynamics. Investigators examined the engine components and the maintenance history of the aircraft. The investigation revealed that while the aircraft had undergone frequent 50-hour and 100-hour inspections, these processes were ineffective at detecting underlying issues. Specifically, the technical personnel failed to identify external corrosion on the cylinder bases and cooling fins during recent inspections.
Findings
- The primary cause of the power loss was the rupture and detachment of the number 4 cylinder due to advanced corrosion that weakened the cylinder walls, leading to fatigue failure.
- The aircraft was operating in a coastal environment near Pisco, which is classified as a severe corrosion environment according to the manufacturer's service manual.
- Maintenance procedures failed to account for the increased inspection frequency required for operations in severe corrosive environments.
- Maintenance inspections were frequent but flawed, as they failed to detect the progression of pitting corrosion on the engine components.