User manual

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As an aircraft burns fuel it loses weight. So, as a flight proceeds, the
altitude at which it can fly efficiently increases. Air traffic control will
permit the air-craft to step climb to the most efficient altitude if traffic
permits. Planning a vertical route between a departure airport and a
destination airport there-fore depends on the decreasing weight of the
aircraft.
Forecasts of the weather to be encountered during the phases of flight
have to be taken into account in order to minimise fuel burn. The wea-
ther effects may only mean an adjustment in cruise altitude, or may re-
quire re-routing around storm cells.
Approaching the planned destination airport, the aircraft will normally
commence its descent for landing at the top of descent (TOD). The alti-
tudes flown during descent are specified in a standard terminal arrival
route (STAR), if used, and may be overridden by air traffic control.
Alternate Airports
Regulations require that a flight plan has a Take-off Alternate airport to
which the aircraft can fly if the departure airport is no longer available
for a flight which has to land shortly after take-off.
The flight plan also has to nominate appropriate Adequate Airports in
case there is a need to land during the en route phase of flight.
And lastly, the flight plan has to nominate Destination Alternate airports
in case the planned destination airport is not available for landing.
Usually one Destination Alternate airport is required when planning a
flight under Instrument Flight Rules (IFR). Some operations may be plan-
ned without Destination Alternate; during certain (weather) conditions
even two Destination Alternates may be required. Special rules apply
when operating to isolated destinations where no Destination Alternate
is available.
For Extended Range (ETOPS) operation additional ETOPS Alternates may
be required.