What happened
On December 7, 2010, a Raytheon Beechjet 400A, registration SE-DRS, was performing a private flight from Tallinn, Estonia, to Kokkola-Pietarsaari, Finland. During taxiing at Tallinn, the crew noted a heading warning indicating a significant discrepancy between the aircraft's magnetic sensors. Suspecting that metal reinforcement in the taxiway concrete was distorting the magnetic field, the commander shut down the engines to restart the systems, which temporarily cleared the warnings.
Shortly after takeoff, the heading discrepancies reappeared and escalated. During the climb, the crew experienced a loss of navigation data and flight director information. In an attempt to resolve the escalating avion and electronic issues, the commander switched off the avionics master switch. This action resulted in the loss of attitude information on the primary flight displays and the disappearance of the navigation database.
With the primary navigation systems compromised, the crew relied on standby instruments and requested radar assistance. Due to deteriorating weather at the intended destination, the crew diverted to Tampere-Pirkkala. The landing was successfully completed using a Precision Approach Radar (PAR) guidance.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the technical failures and the crew's response. The investigation focused on the cause of the magnetic heading split and the subsequent loss of the navigation database. Investigators analyzed the aircraft's maintenance history, the impact of the avionics master switch reset, and the effectiveness of the manufacturer's service bulletins.
Findings
- The initial heading discrepancies during taxi were likely caused by magnetic field distortions from metal objects in the ground.
- The loss of the navigation database and flight plan data occurred because the batteries in the FMC and MDC units were depleted.
- When the crew deactivated the avionics master switch in flight, the remaining battery capacity was insufficient to maintain the database information.
- The aircraft's crew was properly qualified, and the aircraft held a valid certificate of airworthiness.
- The failure to implement recommended manufacturer service bulletins regarding additional battery installations left the system vulnerable to power loss.
- The crew's decision to use a PAR approach at Tampere was appropriate given the lack of functional primary flight instruments.