What happened
On May 3, 2013, a Jetstream 3200, registration ES-PJR, operated by AS Avies, was performing a commercial takeoff from Sveg Airport in Jämtland, Sweden. Shortly after departing the runway, the aircraft experienced severe oscillations in power across both engines. This occurred during a critical phase of flight at a low altitude while the aircraft was accelerating from low speed.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the flight data and cockpit voice recordings, alongside a technical inspection of the aircraft. The investigation focused on the engine configuration and the mechanical state of the turboprop engines. Investigators analyzed the RPM levers and the possibility of spontaneous movement. The technical inspection also revealed corrosion on the aircraft and identified several technical remarks that had not been recorded in the aircraft's official logbook.
Findings
Technical analysis established that the engine oscillations were caused by a too low RPM during the takeoff phase. This specific engine configuration—where power output is high but RPM is insufficient—is a known characteristic of this aircraft type that can trigger such oscillations.
Several contributing factors were identified:
- The aircraft lacks a takeoff configuration warning system, meaning the crew had to rely on manual verification to ensure the RPM levers were in the correct position.
- The crew was not sufficiently aware of the specific flight safety risks associated with low RPM during takeoff.
- Discrepancies were found in the operator's manuals, specifically regarding the terminology used for engine lever positions.
- The operator failed to follow proper procedures for maintaining flight logs and documenting technical remarks.
Safety action
Based on the severity of the incident, the SHK issued recommendations to EASA regarding the following:
- Evaluating the installation of a warning system to alert pilots of incorrect engine configurations during takeoff.
- Revising emergency checklists so that procedures for managing engine oscillations are implemented as memory items.
- Enhancing initial and recurrent pilot training to specifically address the risks of incorrect engine configurations during the takeoff phase.