Date: 202201
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: AC Generator/Alternator
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Troubleshooting; Situational Awareness; Confusion; Human-Machine Interface; Communication Breakdown
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Diverted; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: During cruise at FL330; the Flight Engineer brought to the Captain's attention an illuminated #3 CSD (Constant Speed Drive) Oil Pressure Low Light. The Captain elected to call company Maintenance Control to bring them into the decision-making process regarding running of checklists and possible post-flight MEL options. The Flight Engineer and Captain accomplished the associated checklist for the CSD LOW PRESS LIGHT ILLUMINATED; subsequently disconnecting the CSD. There was no further incident until the approach phase of flight nearing ZZZ1 airport. Upon the Captain's call for selection of flaps 2;" the aircraft experienced #1 and #2 engine-driven AC generators tripped; with associated under-excitation faults Systems 1 and 2; #2 Generator Breaker and #2 Generator Field lights illuminated and the #1 Generator Breaker and #1 Bus Tie Breaker lights illuminated. The Flight Engineer attempted to select the essential power source to STBY but was unsuccessful in restoring essential power using the STBY source. The Engineer attempted then to close the #1 Bus Tie Breaker; which was unsuccessful. At this time the essential power source was selected to the #1 GEN. The Captain had the First Officer [request priority handling] and diversion to ZZZ2 airport where an otherwise normal approach to landing was accomplished.[The problem was identified] upon loss of electrical power with associated loss of lights and instruments. [The cause was] unknown electrical system irregularities and malfunctions. [Responded with an] attempt to restore and protect essential power to the Captain's instruments following procedures and checklists for the related system failures. Subsequently; when it was determined normal course of procedures and checklists would not fully resolve our issues; the decision to [request priority handling] due to loss of electrical power systems and diversion to the nearest suitable airfield with ATC and ARFF (Airport Rescue and Fire Fighting) services."




Synopsis: Captain reported multiple failures of electrical system components after the #3 CSD failed and disconnected; proceeded to request priority handling; and diverted to a precautionary landing.