AP/FD CLIMB MODES The AP/FD climb modes may be either • Managed • Selected MANAGED The managed AP/FD mode in climb is CLB. Its use is recommended as long as the aircraft is cleared along the F-PLN. SELECTED The selected AP/FD modes in climb are OP CLB, V/S and EXPED r* . OP CLB is to be used if ATC gives radar vector or clears the aircraft direct to a given FL without any climb constraints. The use of low values of V/S, e.g. less than 1 000 ft/min, may be appropriate for small altitude changes as it makes the guidance smoother and needs less thrust variation. In areas of high traffic density, low values of vertical speed will reduce the possibility of nuisance TCAS warnings. If the crew selects a high V/S, it may happen that the aircraft is unable to climb with this high V/S and to maintain the target speed with Max Climb thrust, for performance reasons. In that case, the AP/FD will guide to the target V/S, and the A/THR will command up to Max Climb thrust, in order to try to keep the target speed; but the aircraft will decelerate and its speed might reach VLS. When VLS is reached the AP/FD reverts to OP CLB and the aircraft accelerate to initial target speed. Whenever V/S is used, pilots should pay particular attention to the speed trend as V/S takes precedence over speed requirements. The EXPED mode r* is used to climb with maximum vertical gradient i.e. the target speed becomes green dot. Its use should be avoided above FL 250. The crew should be aware that altitude constraints in the MCDU F-PLN page are observed only when the climb is managed, i.e. when CLB is displayed on the FMA. Any other vertical mode will disregard any altitude constraints. A likely scenario would be, when the FCU altitude is set above an altitude constraint and the pilot selects V/S when below that constraint to avoid a potential TCAS TA. In this case, the aircraft will disregard the altitude constraint.
Posted on: Tue, 20 Aug 2013 18:26:42 +0000
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