What aircraft was involved and where did it happen?

The accident on 2023-07-30 involved an aircraft, registration 9A-DMA, at HR.

Engine Failure Leads to Forced Landing of Cessna 172N in Sinj (9A-DMA)

On July 30, 2023, an aircraft (registration 9A-DMA) was involved in an aviation accident near HR. Investigators recorded the probable cause as: The engine power loss was caused by mechanical failure of the rocker arms on cylinder number 4 due to carbon buildup from improper combustion, exacerbated by maintenance intervals that were less frequent than manufacturer recommendations. This summary draws on records from the Air, Maritime and Railway Traffic Accident Investigation Agency of Croatia (AIN).

Sourcesthe Air, Maritime and Railway Traffic Accident Investigation Agency of Croatia (AIN)Primary reportUpdated 1785055897Data API Editorial standards

A Cessna 172N experienced a significant loss of engine power during a training flight, resulting in a forced landing and damage to the aircraft near Sinj Airport.

What happened

On July 30, 2023, at approximately 17:30 local time, a Cessna F172 N, registration 9A-DMA, was performing a flight for the purpose of renewing a pilot's license at Sinj Airport. During the initial climb phase following takeoff from runway 26, the pilot reported a lack of full engine power and abnormal engine noise.

The instructor took control of the aircraft and initiated a 150-to-18 and 180-degree left turn to return to the airport. While attempting to realign with the runway, the crew encountered a glider on final approach. To avoid a mid-air collision, the instructor executed a 250-degree right turn. Due to the insufficient engine power, the aircraft was unable to maintain altitude. The aircraft struck the treetops with its right wing and subsequently made a forced landing in a meadow approximately 400 meters from the runway. The aircraft sustained significant damage to the fuselage, wings, propeller, and landing gear. Both the pilot and the instructor sustained injuries.

The investigation

The investigation examined the engine's mechanical condition, maintenance records, and the aircraft's maintenance program. Investigators found that the engine's spark plugs were heavily covered in carbon deposits, indicating improper combustion. The investigation also reviewed the aircraft's maintenance program (POZ), noting discrepancies between the operator's scheduled inspections and the manufacturer's instructions. Specifically, while the manufacturer's service instruction (SI 1009) required annual inspections, the operator's program implemented three-year intervals.

Findings

The primary cause of the engine power loss was mechanical damage to the intake and exhaust valve rocker arms on cylinder number 4.
This damage was caused by excessive compressive force on the rocker arms, resulting from restricted valve movement.
The restricted movement was caused by carbon buildup around the valve, which was a result of improper fuel combustion.
The aircraft's maintenance program was not fully aligned with the manufacturer's instructions, specifically regarding the frequency of engine inspections.
The engine type (Lycoming O-320-H2AD) has a known history of various service bulletins and airworthiness directives related to component wear and mechanical issues.

Probable cause

The engine power loss was caused by mechanical failure of the rocker arms on cylinder number 4 due to carbon buildup from improper combustion, exacerbated by maintenance intervals that were less frequent than manufacturer recommendations.

Engine failure

2023-07-30: (9A-DMA) — HR