A reclear flight plan has two destinations . The final destination airport is where the flight is really going to , while the initial destination airport is where the flight will divert to if more fuel is used than expected during the early part of the flight . The waypoint at which the decision is made as to which destination to go to is called the reclear fix or decision point . On reaching this waypoint , the flight crew make a comparison between actual and predicted fuel burn and check how much reserve fuel is available . If there is sufficient reserve fuel , then the flight can continue to the final destination airport ; otherwise the aircraft must divert to the initial destination airport .
The initial destination is positioned so that less reserve fuel is needed for a flight from the origin to the initial destination than for a flight from the origin to the final destination . Under normal circumstances , little if any of the reserve fuel is actually used , so when the aircraft reaches the reclear fix it still has ( almost ) all the original reserve fuel on board , which is enough to cover the flight from the reclear fix to the final destination . The idea of reclear flights was first published in Boeing Airliner ( 1977 ) by Boeing engineers David Arthur and Gary Rose . The original paper contains a lot of magic numbers relating to the optimum position of the reclear fix and so on . These numbers apply only to the specific type of aircraft considered , for a specific reserve percentage , and take no account of the effect of weather . The fuel savings due to reclear depend on three factors :
• The maximum achievable saving depends on the position of the reclear fix . This position cannot be determined theoretically since there are no exact equations for trip fuel and reserve fuel . Even if it could be determined exactly , there may not be a waypoint at the right place .
• One factor identified by Arthur and Rose that helps achieve the maximum possible saving is to have an initial destination positioned so that descent to the initial destination starts immediately after the reclear fix . This is beneficial because it minimises the reserve fuel needed between reclear fix and initial destination , and hence maximises the amount of reserve fuel available at the reclear fix .
• The other factor which is also helpful is the positioning of the initial alternate airport .
A - Z of Flight
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