What happened
On October 10, 2021, a Cessna 172XP, registration HK-5032, was conducting a non-scheduled commercial cargo flight from Mitú to Yapú, Colombia. Shortly after departing from the Fabio Alberto León Bentley Aerodrome, the pilot experienced periodic drops in engine RPM, resulting in a substantial loss of engine power and airspeed.
After notifying air traffic control and requesting an immediate return to the airport, the pilot attempted a 45-degree turn to intercept the runway. During this maneuver, the pilot identified high-voltage power lines in the flight path and diverted the turn to avoid them. Unable to maintain sufficient altitude and speed to reach the runway, the pilot selected an unprepared area of light forest for an emergency landing.
During the final approach, the aircraft's main landing gear struck the treetops, causing the aircraft to decelerate sharply and the left horizontal stabilizer to detach. The aircraft subsequently impacted the ground. The pilot sustained minor injuries and was able to evacuate the aircraft independently.
The investigation
The GRIAA investigation focused on the mechanical failure of the engine components. Investigators performed a general inspection of the engine and a detailed metallurgical analysis of the rocker arm bolts. The examination revealed that the engine's performance was severely compromised when the failure of one cylinder caused a secondary failure in the opposite cylinder due to the engine's opposed design.
Technical analysis of the rocker arm bolts showed evidence of material aging and intergranular corrosion caused by exposure to varying atmospheric and geographic environments. The investigation also scrutinized the operator's maintenance manuals, finding that they lacked specific procedures for the periodic inspection of these critical bolts and did not establish a definitive service life for them.