Transport Canada CF-2023-78

Requires revising the airplane flight manual, verifying aircraft technical records, cleaning of printed circuit boards, and modification of the left-hand direct current power center (DCPC) internal communication data bus units. Prompted by multiple in-service reports of erratic electrical system status on the push button annunciators and EICAS while on-ground and during flight. Several of these incidents resulted in the airplane experiencing a momentary loss of electrical power and loss of flight displays following crew action. During the investigation, it was found that airplanes can experience misleading electrical system status indications as a result of contamination of electrical contacts in the left-hand DCPC internal communication data bus. The erratic indications could cause the crew to turn off fully operational electrical power sources, leading to partial or complete loss of electrical power.