What happened
On June 21, 2017, at approximately 11:33 UTC, a Boeing 738 operating a flight from Kraków (LGKK) to Prague (LGPR) encountered an electrical system malfunction. During the flight, the crew received a "MASTER CAUTION - ELEC - RIGHT SOURCE OFF" warning, indicating that the generator for the number two engine had failed and disconnected from the electrical system.
In response to the warning, the crew followed the established non-normal checklists (NNC) for a "SOURCE OFF" event. They successfully started the Auxiliary Power Unit (APU) and connected the APU generator to the aircraft's electrical network. Following these procedures, the crew continued the flight to the destination airport, where the aircraft landed safely.
The investigation
The investigation, conducted by the operator, focused on the technical failure of the electrical component. Following the incident, the captain notified the Maintenance Control Center (MCC) and recorded the malfunction in the aircraft technical log.
Maintenance personnel performed an inspection of the electrical installation according to the Flight Interruption Manual (FIM). While the initial inspection did not reveal an immediate fault, a subsequent test was performed after restarting the number two engine. During this test, the generator failed to engage. Consequently, the generator was disconnected, and the aircraft was cleared for further flight under the provisions of the Minimum Equipment List (MEL) regarding the engine-driven generator.
On June 24, 2017, the generator was replaced in accordance with the Aircraft Maintenance Manual (AMM). Following the replacement, a functional test was conducted with positive results, and the aircraft was returned to service without restrictions.
Findings
- The primary cause of the incident was the malfunction of the number two engine generator.