What happened
On 31 January 2003, a British Aerospace ATP, registration SE-LGZ, was conducting a scheduled freight flight from Stockholm/Arlanda to Helsinki. Approximately 15 minutes after departure, while cruising at 5,800 meters, the aircraft experienced a sudden and total loss of power within its right-hand electrical system. This failure resulted in the immediate loss of all flight and navigation instruments (EFIS2) on the right side of the cockpit.
As the electrical failure progressed, warning lights illuminated on the emergency panel, and the blue mimic line on the right-hand generator switch disappeared. The crew attempted to restore power by cycling various systems; while they briefly regained normal electrical function, the failure recurred within a minute. Fearing that the remaining systems were running solely on battery power, the pilots requested a return to Stockholm/Arlanda. The aircraft landed safely on runway 01L without the use of flaps.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the aircraft's electrical architecture, specifically the 28V DC and 115V AC systems. The investigation focused on why the right-side instruments failed and why the crew was unable to identify a solution via the onboard documentation. Investigators reviewed the technical status of the Reverse Current Circuit Breakers (RCCB) and the usability of the existing emergency checklists.
Findings
- The electrical failure was triggered by two independent faults occurring simultaneously within the aircraft's electrical system.
- One of these faults involved a component from an earlier production version that possessed known technical weaknesses.
- The crew was unable to effectively utilize the emergency checklist because the document was not user-friendly, featuring small typeface, complex logic, and a lack of clear headings that corresponded to the warning panel messages.
- Although the pilots could have potentially restored full electrical function by cross-connecting the left and right AC systems, the checklist did not serve as an intuitive guide for this action.
Safety action
Following the investigation, SHK issued recommendations to the Swedish Civil Aviation Administration to consider the design and comprehensibility of emergency checklists during the issuance of Air Operator Certificates (AOC). Furthermore, the authority advocated for the development of an international standard regarding the layout, logic, and arrangement of emergency checklists in professional aviation to ensure they serve as effective safety aids during high-stress situations.