B777-200
Flight Crew Air Transport Pilot (ATP)
Fatigue
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance
Human Factors
On climb out on our second leg (after flying 10hrs31min) we were given a 5;000 feet level off. The aircraft over shot by seven hundred feet. We began a descent back to 5;000 feet. It was only a momentary over shoot. The pilot monitoring called out the deviation. There was no contact about the over shoot with ATC. We were all so tired that no one really cared. 2nd leg of a 12 hour flight is unsat and unsafe. We were dangerous the rest of the flight. In hind sight I should have stopped the jet at the original destination.We were fatigued and unsafe due to our schedule and time zone changes.Do not schedule multiple legs and use 2 extra pilots to justify over 12. It is impossible to get proper rest when the legs are broken up with 10 hours and 2 hours. 8 time zones with an arrival that is at the bottom of our base time (6:00am).
B777 international Captain reported extreme fatigue was a factor in overshooting a cleared altitude on leg two following a 10:31 first leg.