Flight crews should not cross more than 12 time zones east or west of their home base in one duty cycle. Individual duty period for ultra-long-range flights will be limited by the number of crew members on board and rest facilities (bunks) provided. Rest periods normally to be granted in accordance with crew member's home base body clock for the first 72 hours of duty. Recovery periods introduced at the end of a duty cycle to allow crew members' body clocks to resynchronise to home base time (may be up to six days depending on the number of time zones crossed or length of previous duty cycle). 190 duty hours limit in 28-day period reduced by eight hours each time six or more time zones are crossed during that 28-day period.