What aircraft was involved and where did it happen?

The accident on 2011-05-16 involved a AS350 B2,, registration I-AIRY, at Località Lasa (BZ), IT.

What was the probable cause of the accident?

The engine failure was caused by an accumulation of environmental debris in the oil to fuel heater, which blocked the fuel inlet and led to fuel starvation via FCU cavitation. Contributing factors included the lack of a maintenance task to monitor heater flow, the absence of a protective screen on the fuel filler…

Engine failure caused by fuel heater blockage in AS350 B2

An AS350 B2 helicopter experienced an engine shutdown during a transfer flight near Lasa, Italy, due to debris clogging the oil to fuel heater.

What happened

On May 16, 2011, an AS350 B2 helicopter, registration I-AIRY, was performing a transfer flight from Merano to Curon-Venosta for aerial work operations. While cruising at approximately 4,300 feet AMSL, the engine suddenly shut down. The pilot reported hearing a loud bang from the rear of the aircraft, accompanied by a sudden yaw to the right and a rapid decrease in main rotor RPM.

Upon confirming the engine failure via instrument readings—specifically low oil pressure and falling T4 and NG indications—the pilot initiated an autorotation. The pilot successfully performed an emergency landing at a nearby base in Lasa. There were no fatalities or injuries among the three occupants, though the aircraft sustained minor damage to the main rotor blades and landing skids.

The investigation

The ANSV investigation focused on the engine's Fuel Control Unit (FCU) and the oil to fuel heater, a component installed as part of a de-icing system. Investigators examined the fuel system, including the fuel filter and the intake area. Laboratory analysis of the material found inside the oil to fuel heater revealed that the inlet passage was blocked by environmental dust and debris.

Testing confirmed that the contaminants were a mix of natural and anthropogenic particles from the external environment. The investigation also looked into the refueling practices of the operator and the physical configuration of the aircraft's fuel filler neck. It was noted that the aircraft lacked the protective screen found on later AS350 B3 models.

Findings

The primary cause of the engine shutdown was the blockage of the oil to fuel heater inlet passage.
This blockage caused a pressure drop that led to insufficient fuel pressure at the FCU, resulting in pump cavitation and the interruption of fuel flow.
The maintenance program lacked a specific task to periodically check the fuel flow through the heater to detect potential clogs.
The heater was located upstream of the main fuel filter, meaning contaminants could reach the component without being intercepted.
The practice of refueling with rotors in motion, combined with the lack of a protective screen on the filler neck, allowed environmental debris to enter the fuel system.

Safety action

The ANSV recommended that ENAC consider updating maintenance programs for AS350 helicopters equipped with the SB 28.00.09 modification to include periodic fuel flow checks for the oil to fuel heater.
The ANSV recommended that EASA evaluate the issuance of a Service Bulletin to provide an optional protective screen for the fuel filler neck on older AS350 models.