What happened
On June 13, 2016, at approximately 04:51 UTC, a Saab SF-3able operated by SprintAir SA experienced an electrical malfunction during the climb phase. The incident occurred roughly eight to ten minutes into the flight, shortly after the aircraft exited the Warsaw (EPWA) Terminal Control Area (TMA).
During the ascent, the crew observed the activation of the "ELEC" warning light on the Captain's Pilot Position (CWP), along with associated warnings for the "R ESS BUS" and "R MAIN BUS" on the upper panel. This failure resulted in a loss of indications across several flight instruments and the malfunction of equipment connected to the right essential and main power buses.
Following the detection of the failure, the crew executed the Abnormal checklists (A18 and A19) and consulted the Electrical Power Distribution List. The crew subsequently decided to return to Warsaw (EPWA). Due to the failure of the landing gear position indicator, the crew requested a low-level pass over the runway to allow the Tower to visually confirm the gear configuration. This maneuver was completed at 05:13 UTC, and the aircraft landed safely at 05:27 UTC.
The investigation
The investigation focused on the electrical distribution system of the aircraft to identify why the power buses lost stability. The technical examination centered on the integrity of the circuit protection components within the electrical system.
Findings
- The primary cause of the electrical failure was the malfunction of the S7 fuse, which serves the "R ESS / R MAIN" bus.
- Replacing the faulty S7 fuse resolved the issue and restored normal electrical operations.