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Cruising faster at 10000ft reduces the time penalty at the expense of fuel.
After a long flight with an A340–500 or –600, starting the descent some 100nm early would not appear to be significant in the overall flight. However this can result in a 900kg fuel burn increase and 8 minutes longer block time.
5.5 HOLDING
5.5.1 INTRODUCTION
When holding is required, it is generally flown on a “race track pattern”, composed of two straight legs plus two 180 degree turns. In a hold the distance covered is not the primary objective. On the contrary, the knowledge of the maximum holding time (maximum endurance) is a determining factor for any diversion decision. As a result, it is important, during holding, to try to minimize fuel by simply minimizing fuel flow.
For all aircraft, the minimum fuel consumption speed is very close to the maximum lift-to-drag ratio (Green Dot) speed as shown below. As a result, in clean configuration, the standard holding speed is selected equal to green dot speed (GD).
Holding patterns may be quite limiting around certain airports due to obstacle proximity. Therefore, green dot is sometimes too high, especially during turn phases where the bank angle can be too significant. As it is not possible to significantly reduce the speed below green dot in clean configuration, slats may be extended and a holding done in CONF1 at “S” speed. (min slat retraction speed Conf 1 to Conf clean).
At other airports, Air Traffic Control may require the hold to be performed at a certain speed, and it may not be possible fully optimise the fuel burn. In order to allow flexibility in planning and operations, the FCOM has four different holding speed and configuration combinations, adapted to each type of aircraft.
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