Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 240; Flight Crew Total 22000; Flight Crew Type 14000
Fatigue; Situational Awareness
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Aircraft; Human Factors
As Captain of the flight I accept responsibility for these issues and wish to bring some of them to light. I back up my flight attendants fully. There are some items that the [company] must share with [our flight attendants]. I have witnessed a vast number of new hires. I appreciate our flight attendants and am not pointing fingers; but we need to discuss some things.First; when the pilots need food; coffee; and restroom breaks; they are needed then; not in 2 hours or more.We were in cruise; 1 hour out; briefed the arrival and completed the checklist. This was day 5 of 6 for me and I was tired; so I drank 2 cups of coffee prior to TOD. I asked for a restroom break well prior to TOD; and got it just prior to TOD; because the flight attendants were busy. I left quickly and when I was gone my experienced FO started down. I returned to the cockpit and we were going high at SLT. I announced this and he clicked the AP off and manually flew down to FL180. We crossed 400 feet high and nothing was said by ATC. We landed uneventfully.Problems encountered: VNAV has been very slow lately and I tell my FOs to put a fix 3 miles prior to the crossing altitude so we don't get ALTCAP and bust the altitude. This usually works. I don't understand why the VNAVs are acting up like this? We wrote up the VNAV. I've flown this airplane for [many] years and this is bugging me. Can you shed some light on this? Please; make a bulletin and share this with [flight attendants]? I will not leave the flight deck with an inexperienced FO; at TOD.
B757 Captain reported failure to meet a crossing restriction; with a last minute restroom break cited as contributing.