B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 174; Flight Crew Type 1557
Fatigue
No Specific Anomaly Occurred All Types
General None Reported / Taken
Human Factors
This story begins with an early morning commute. Upon landing in ZZZ1; my FO [First Officer] for this same pairing and who also commuted in on the same flight; advised me that the amount of duty time for Day 1 (9:54) which included 1 leg to ZZZ2 prior to a red eye from ZZZ2 to ZZZ may be over the duty limits imposed in [Union Agreement] of 9:45. I wasn't familiar with that provision and as such fired off a [report] to the Union Scheduling Committee for additional information. I then went to the crew and went back to sleep for about 2 hours before waking up around noon to use the bathroom. I checked my email; saw no reply from the union; and went back to sleep until [time] local time. I grabbed lunch and a coffee and checked my email for a reply on my [report] - there wasn't one. I would characterize the sleep as good quality and my alert status as ramping up. Once in the crew room for preflight planning; I relayed this duty question to a couple of other pilots and they were eager for a response because they too had 2 leg red eyes. Still with no email response; I called the [Chief Pilot] and asked to speak with the 'contract expert' but he [was] out for lunch. I relayed my question to the [Chief Pilot] and he thought the trip was legal but would have the expert call me back. I shared this info with the other pilots and proceeded to my gate where I met my FO. He had gone to his crash pad for a nap. After I was in the cockpit; the contract expert called; I put him on speaker so the FO could hear the conversation. He explained that since we would be landing in ZZZ at XA09 ZZZ time; this trip wasn't 'legally' considered All Night Flying per the [union agreement] and hence legal. So off we went...It was an uneventful flight to ZZZ2 and while waiting for our delayed inbound flight; I grabbed another large coffee for the leg to ZZZ. I would say I was fairly alert but not looking forward to 5 hours of more flying. Despite having to take a more southerly route for weather avoidance; it was an uneventful flight until about 3 hours left to go. That's when I hit the proverbial 'wall' and exhaustion set in. I alerted my FO to my situation and requested another restroom break and another beverage. I splashed water on my face and did some stretching to wake myself up. It seemed to help a little but I knew I wasn't firing 'on all cylinders' and tried to gut it out as the skies continued to brighten as the sun came up. With about an hour or so to go; we requested and took another bathroom break for more water splashing and stretching. I declined any more caffeine and tried to sip water to help me stay alert but nothing seemed to work for long. By the grace of God; nothing went wrong for the rest of the flight and no emergencies popped up and we landed successfully in ZZZ. We did miss the first crack at the hotel shuttle though as the driver didn't see us crossing the street and pulled off without us. While at the curb; we read the email reply from the union and agreed to discuss any possible fatigue calls after we woke up. But after sleeping for 9 hours straight; I felt fine to continue. I wasn't fatigued at that point but I was earlier in the previous flight. Which gets to the crux of my concerns; which is what do I do now that I know I'm fatigued while I'm flying?
B737 Captain reported a fatigue situation and the events during this rotation.