What happened
On March 16, 2011, a Eurocopter AS 332 L1 operated by the German Federal Police was conducting a multi-leg mission involving several intermediate landings. While flying near Augsburg under instrument flight rules (IFR), the crew was transitioning from flight conditions involving potential icing to warmer air.
During the flight, the crew had previously activated anti-ice systems, including the Multi Purpose Air Intered (MPAI) in the closed position, due to observed temperatures of 0 °C and visible precipitation. As the aircraft reached warmer air, the crew began deactivating non-essential systems. The second pilot, intending to perform a sand filter test, verbally announced the intention to open the MPAIs. Following a brief confirmation from the first pilot, the second pilot switched both MPAIs to the "OFF" position, opening the intakes. Approximately five seconds later, both engines failed simultaneously.
The crew initiated an autorotation and declared an emergency. During the descent, the crew successfully restarted the left engine at approximately 300 ft AGL. However, upon restarting the right engine, the crew noted unusual vibrations and a warning light indicating metal particles in the main gearbox. Fearing a gearbox failure, the crew diverted to a nearby airfield, but eventually decided to proceed to Augsburg after encountering further issues with rotor RPM regulation. The aircraft landed safely in Augsburg after the crew corrected the engine power lever position.
The investigation
The BFU examined the aircraft's flight data, cockpit voice recordings, and the mechanical condition of the engines and gearboxes. The investigation included an analysis of the meteorological conditions, which confirmed that icing conditions were possible in the area. The investigators also reviewed the crew's training, the airline's operational procedures, and the aircraft's equipment standards. Notably, the investigation revealed that the aircraft was not equipped with a Flight Data Recorder (FDR), despite regulatory requirements for aircraft of this class.
Findings
- The primary cause of the dual engine failure was the improper operation of the engine air intake anti-ice system.
- The presence of undetected ice on the MPAIs contributed to the failure when the intakes were opened.
- Low visibility due to darkness prevented the crew from visually confirming the state of the intakes.
- The Federal Police operated a mixed fleet with differing anti-ice procedures, which may have led to confusion.
- Inadequate crew resource management (CRM) was noted, specifically regarding the lack of consistent communication during the procedure.
- The flight manual procedure allowed for the opening of the MPAIs during flight, which contributed to the event.
Safety action
Following the incident, the manufacturer, Eurocopter, issued a Safety Information Notice warning of potential engine damage from ice ingestion. The BFU issued safety recommendations to the LBA to ensure stricter oversight of aircraft equipment requirements (specifically FDR installation) and to the Federal Police to ensure all AS 332 L1 aircraft are equipped with flight data recorders. Additionally, a recommendation was made to the manufacturer to revise the flight manual so that MPAIs are only opened after engine shutdown on the ground.