What happened
On December 14, 2017, a Piper PA46 350P JetProp DLX, registration D-EVSM, was conducting a business flight from Memmingen Allgäu to Stavanger Sola when the crew encountered a series of technical failures over the North Sea. While descending through FL 260, the pilot and passenger heard a metallic grinding noise followed by the smell of electrical fumes. Fearing an electrical fire, the pilot initiated a high-speed emergency descent and selected the landing gear to the down position to use the gear as a speed brake.
During this sequence, a hydraulic line fractured, causing the system to lose pressure and leaving the landing gear in a partially extended state. The pilot attempted to manage the aircraft while performing load shedding to mitigate the perceived electrical emergency. Upon approaching Aalborg (EKYLE), the pilot attempted to land despite the gear malfunction. During the landing roll, the aircraft skidded off the right side of the runway into the safety area. There were no injuries to the occupants.
The investigation
The Danish Accident Investigation Board examined the aircraft's hydraulic and electrical systems, as well as the pilot's workload and the onboard documentation. The technical inspection of the hydraulic system identified a fatigue fracture in the hydraulic down line, likely caused by a material defect. This fracture led to the depletion of the pump reservoir. The investigation also found that the hydraulic pump circuit breaker had tripped, likely due to the pump operating without pressure for an extended period.
Investigators also reviewed the emergency procedures checklists. They noted that while the Pilot's Operating Handbook (POH) contained critical information regarding the physical force required to extend the gear, the specific JetProp emergency checklist was ambiguous. The checklist included procedures for different hydraulic systems without clear differentiation, which could lead to confusion during high-stress operations.
Findings
- The primary trigger for the emergency descent was noise and fumes originating from a failed vent/defog blower.
- A material defect in the hydraulic tubing caused a fatigue fracture during the gear extension attempt.
- The pilot's ability to troubleshoot the landing gear was severely hindered by task saturation and high workload caused by managing the electrical smoke, communicating with ATC, and navigating deteriorating weather.
- The pilot did not utilize the autopilot to its maximum extent, which could have reduced the mental workload.
- The onboard JetProp emergency checklist contained ambiguities regarding which hydraulic procedures applied to the specific aircraft serial number.