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Old 28th Jul 2009, 05:58
  #19 (permalink)  
Tinstaafl
 
Join Date: Dec 1998
Location: Escapee from Ultima Thule
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If you're using fuel as ballast then ZFW is still ZFW - it's just a different ZFW. One that is a bit heavier than normal. Fuel used as ballast can't be planned as useable fuel. As far as W&B and Endurance is concerned ballast fuel may as well be bricks with an SG of .71 occupying space in the fuel tank that normally would be burnable fuel.

Duty time problems can have more than one independent rest periods. You need to use the most limiting. For example, think of a case where there is a rest period based on *duty* time, and a rest period based on *flight* time and a rest period based on finishing late. Even though duty time hasn't been extended, flight time has been and it was into a late finish with an option for duty length the next day. The rest period due to duty is 'x'. Rest period due to flight time is 'x+an additive'. Rest period due to finishing late is 'x + something if the following day is shortened' *OR* 'x + something else' if the following day is not shortened.

You need to work through each option that the F&D time limits gives you and choose the most limiting. Bear in mind that they're not usually additive in the sense that you exceed two or more limits so you think you must combine all extra rest additives.
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