Narrative:

On a repositioning flight; without passengers; operated under part 91 we encountered a fluctuation of the automatic cabin pressure control system during an ocean crossing from ZZZ to ZZZ1. I was the pilot in command and pilot flying when the pilot not flying came back to the cockpit from the cabin to inform me of a sound coming from the baggage door. I checked the automatic cabin control system and did not see any reason for concern; all parameters were within limits. The pilot not flying went back to the cabin and felt the need to rest. I requested and received block altitude of FL400 to FL450. I climbed to FL430 and began to notice the cabin start to climb with the outflow valve fully closed. I told the pilot not flying to return immediately to his seat. At that time I began a descent down to FL400 and the cabin psi normalized. I told the pilot not flying to request a lower flight level and the controller responded with clearance to FL380. I then asked the pilot not flying to plot our location and tell me if we have passed our etp. Without hesitation he said 'we have passed the etp and we should continue.' the controller asked if we had a problem and the pilot not flying said we are having cabin psi variations and we will advise shortly. A minute or so passed and then I responded to a red 'cabin pressure low' message by calling for the checklist and donning my oxygen mask. I told the pilot not flying to request a lower altitude again. And the controller responded and said he can't clear us for lower at that time. We remained at FL380 and I handed the pilot not flying my checklist because he had trouble finding the one next to him. The controller suggested a right turn offset if we needed due to traffic. The checklist was completed and the cabin had stabilized. I then wanted the pilot not flying to show me the plot he made that proved we had passed the etp. He did not say a word and stared at the plotting chart. He then threw the chart at me and said 'you do it.' perplexed at that; I plotted our location and we were over a hour before reaching our etp. At this time the cabin altitude began to fluctuate again; and I told the pilot not flying to ask for a lower altitude again. The controller asked if we declare 'pan pan;' and I said to say yes and we need time to advise. I decided to offset 4 miles right off course until we worked out a decision and prepared to descend further. I told the pilot not flying to declare an emergency and request a descent to FL320. He refused to declare an emergency and told me to do that myself as well. The cabin altitude began climbing again so I started a descent to FL320. I got on the radio declared an emergency and descended to FL320. At that altitude we were able to maintain cabin pressure. I told the pilot not flying to get back on the radio and request clearance to return. The pilot not flying then asked to return to ZZZ2. The radio controller first cleared us direct xxxxx. I knew xxxxx was too far and told the pilot not flying to ask for a revised clearance towards ZZZ2. The controller then re-cleared cleared us direct ZZZ2. In conclusion; before the event occurred; the pilot not flying 'who is also my employer' had been sitting in the cabin with the flight attendant doing nothing to assist me with the oceanic crossing and was lost when I needed him most. During this flight I realized the importance of CRM and situational awareness of both pilots. If I hadn't plotted our route and maintained situational awareness I would have listened to the pilot not flying and continued and possibly run out of fuel with no alternate airport for landing. One way to prevent this in the future is to make sure the pilot not flying has been trained properly and knows how to assist the pilot flying with important duties.

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Original NASA ASRS Text

Title: A GIV Captain reported difficulty maintaining cabin pressure on a transpacific flight. He declared an emergency and returned to the mainland.

Narrative: On a repositioning flight; without passengers; operated under Part 91 we encountered a fluctuation of the automatic cabin pressure control system during an Ocean crossing from ZZZ to ZZZ1. I was the Pilot in Command and Pilot Flying when the Pilot Not Flying came back to the cockpit from the cabin to inform me of a sound coming from the baggage door. I checked the automatic cabin control system and did not see any reason for concern; all parameters were within limits. The Pilot Not Flying went back to the cabin and felt the need to rest. I requested and received block altitude of FL400 to FL450. I climbed to FL430 and began to notice the cabin start to climb with the outflow valve fully closed. I told the Pilot Not Flying to return immediately to his seat. At that time I began a descent down to FL400 and the cabin PSI normalized. I told the Pilot Not Flying to request a lower flight level and the Controller responded with clearance to FL380. I then asked the Pilot Not Flying to plot our location and tell me if we have passed our ETP. Without hesitation he said 'We have passed the ETP and we should continue.' The Controller asked if we had a problem and the Pilot Not Flying said we are having cabin PSI variations and we will advise shortly. A minute or so passed and then I responded to a red 'Cabin Pressure Low' message by calling for the checklist and donning my oxygen mask. I told the Pilot Not Flying to request a lower altitude again. And the Controller responded and said he can't clear us for lower at that time. We remained at FL380 and I handed the Pilot Not Flying my checklist because he had trouble finding the one next to him. The Controller suggested a right turn offset if we needed due to traffic. The checklist was completed and the cabin had stabilized. I then wanted the Pilot Not Flying to show me the plot he made that proved we had passed the ETP. He did not say a word and stared at the plotting chart. He then threw the chart at me and said 'You do it.' Perplexed at that; I plotted our location and we were over a hour before reaching our ETP. At this time the cabin altitude began to fluctuate again; and I told the Pilot Not Flying to ask for a lower altitude again. The Controller asked if we declare 'Pan Pan;' and I said to say yes and we need time to advise. I decided to offset 4 miles right off course until we worked out a decision and prepared to descend further. I told the Pilot Not Flying to declare an emergency and request a descent to FL320. He refused to declare an emergency and told me to do that myself as well. The cabin altitude began climbing again so I started a descent to FL320. I got on the radio declared an emergency and descended to FL320. At that altitude we were able to maintain cabin pressure. I told the Pilot Not Flying to get back on the radio and request clearance to return. The Pilot Not Flying then asked to return to ZZZ2. The Radio Controller first cleared us direct XXXXX. I knew XXXXX was too far and told the Pilot Not Flying to ask for a revised clearance towards ZZZ2. The Controller then re-cleared cleared us direct ZZZ2. In conclusion; before the event occurred; the Pilot Not Flying 'who is also my employer' had been sitting in the cabin with the Flight Attendant doing nothing to assist me with the Oceanic crossing and was lost when I needed him most. During this flight I realized the importance of CRM and situational awareness of both pilots. If I hadn't plotted our route and maintained situational awareness I would have listened to the Pilot Not Flying and continued and possibly run out of fuel with no alternate airport for landing. One way to prevent this in the future is to make sure the Pilot Not Flying has been trained properly and knows how to assist the Pilot Flying with important duties.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.