The following figures are from the UK CAA publication CAP371 (The avoidance of fatigue in aircrews) Airlines normally have a more restrictive duty linitations.
Duty period depends on number of planned sectors and the time the crew went "on duty"
The maximum number of hours is 14hrs.
To operate for 14hrs the following needs to be achieved:
Firstly the crew must be "Acclimatised" to the local time zone which means the crew have spent 3 local nights in the departure airport's time zone, or a crew member who has had the required rest but has only operated thier last sector (prior to going on rest) within a time zone area of + or - 2 hrs of local time. Eg LHR
- Nightstop - TXL
. This crew member is still said to be acclimatised to the local time zone.
Secondly the crew can only report between 0800-1259 Local time and only operating 1 sector to use the full 14hrs of duty. (You will not find a carrier out there who allows 1 crew to operate 14hrs)
The more sectors you do, the less hours you can operate. The earlier/later you report in the day also reduces your hours. The best time to report is between 0800-1259 Local (for UK regs).
If you are not acclimatised your hours are greatly reduced.
Crews can operate "split duty" where the crew have at least 3 hours of uninterrupted rest, they can then re-claim half of that rest period (90 mins in this case) and use them to bolster thier crew hours.
On Long Haul flights, I know of an airline with the following procedure for flight deck crew:
From Report to off duty
0-9 Hrs 1 Flight Deck Crew
9-12 Hrs 1 Flight Deck Crew plus a Senior FO or second captain
12Hrs+ 2 Flight Deck Crews
Hope this helps