B767-300 and 300 ER
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Hazardous Material Violation
Flight Crew Overcame Equipment Problem; Flight Crew Became Reoriented; General Maintenance Action
Human Factors
We were scheduled to operate the aircraft to ZZZ the previous evening flight. We were operating under FOM Dry Ice Supplemental procedures. This procedure causes us to follow a QRH procedure that requires us to start the APU during loading; turn on the Air Conditioning Packs; set the FWD Cargo Air Conditioner to full cold; and set the Main Deck Temp Select to perishable to keep the level of CO2 down for the load crew and the flight crew. Right before closing up the aircraft to fly back to ZZZ; we had a malfunction of an electrical relay which caused the aircraft to go down. This happened too late for [Operations] to recover the freight. Scheduling put us back into crew rest and the part was flown to ZZZ1.  The aircraft was buttoned up and all the Dry Ice remained on the aircraft while we were in crew rest. 4 containers of courier freight were the only cans removed from the aircraft. When we returned this morning to preflight the aircraft we found the aircraft closed up completely and on ground power only. I immediately went upstairs; checked the AML; and started the APU to get the packs on. I opened up both the Captains and First Officer's windows and turned on the CO2 meters. The alarms on 2 of them were going off immediately. I had the Ramp Agent open the main cargo door and the forward cargo door to try to help vent the aircraft. It took almost 45-60 minutes before we were getting a consistent reading of 0 on the CO2 meters. This ramp constantly operates this flight under the Supplemental dry ice procedures. The previous night we also came out to the aircraft being loaded without the APU or packs running.If we had not had the maintenance problem the previous evening this would not have occurred. The ramp should have unloaded the containers containing dry ice overnight and reloaded the next day or kept the APU and packs running overnight.The ramps need to be trained to configure the aircraft for Supplemental dry ice procedures. In this case if they choose to leave the dry ice on the plane they should have run the packs all night. If this happens again I recommend they remove the dry ice from the aircraft until the packs are running to insure CO2 is at a safe level.
B767 Captain reported dangerously high CO2 levels on aircraft due to incorrect Supplemental Dry Ice maintenance procedure.