Date: 201601
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Generator Drive
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Human factors: Troubleshooting; Communication Breakdown; Confusion
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft; Manuals
Primary problem: Manuals

Narrative: Upon reaching our cruise altitude of FL240 on this flight the Auto-Pilot disconnected; and the Captain (who was Pilot Flying) noticed that the left generator 'BUS OFF' light was annunciated (indicating that the left generator was not being powered by the left engine). The Captain asked me to refer to the QRH (Quick Reference Handbook) for left 'BUS OFF'; which had us connect the left bus to the operating APU. Shortly thereafter; an 'ELECT' annunciator appeared on recall; and the Captain noticed a 'LOW OIL PRESSURE' annunciator for the left CSD (Constant Speed Drive). The Captain pointed to the left CSD; and asked me to refer to the 'Low Oil Pressure' checklist. At this time; the Captain was contacting our Company Dispatch on SELCAL to inform them of our situation; and whether we should return to our departure airport or continue to our destination.As there are two QRH checklists for 'Low Oil Pressure' (one for low oil pressure related to the Engine; and the second for low oil pressure related to the CSD) I mistakenly referred to the incorrect checklist for low oil pressure in the Engine. This low oil pressure checklist for the Engine called for us to perform a shutdown of the left engine. The Captain advised Center that we will need to return to our departure airport. As we were descending from FL240; and given a heading for our return back the Captain questioned whether we did indeed perform the correct checklist (as it seemed odd that we would need to shut down the engine; based on an electrical issue such as what we had with our left CSD failing). I confirmed that we ran the 'Low Oil Pressure' checklist within the 'Engine' tab; and he immediately stated that 'that was the wrong checklist'. I agreed with him that we had indeed performed the wrong checklist; and that the correct checklist would have been 'GEN DRIVE LOW OIL PRESSURE'.Upon both of us agreeing that the incorrect checklist was performed; the Captain asked for me to refer to the correct checklist of 'GEN DRIVE LOW OIL PRESSURE'. We ran that checklist; which called for us to disconnect the left CSD. Upon completion of that checklist; the Captain called for me to refer to the QRH for restart of the left engine we had shutdown. The restart occurred without incident; and we had both engines operating.The Captain advised ATC that we were indeed able to restart the left engine. We continued our descent in VMC; and performed a normal 2-engine approach to landing. Upon touchdown; and as we taxied off of the Runway; ATC asked if we would need any further assistance; and the Captain declared that we would not. We taxied back to the gate without incident.Upon shutdown at the gate; the Captain and I agreed that there was a lack of communication amongst the two of us in dealing with the situation in-flight. The Captain was indeed pointing at the left CSD when the problem occurred in flight; and I should have not rushed myself into referring to what was the incorrect checklist. We both agreed that we should have been more methodical; and less rushed; into addressing the problem. Fortunately; we were able to determine a mistake had been made in performing the incorrect checklist; and did run the correct checklists once that determination had been made. As well; we were able to restart the engine; and continue the flight without incident.We both learned immensely from this situation that when an abnormal condition arises; that we both need to be more methodical; focus entirely on addressing the situation; and do not become distracted with other; less important tasks.




Synopsis: An aircrew experienced a CSD (Constant Speed Drive) failure and mistakenly used the wrong checklist to remedy the situation.