3 Cruise
_ The cruise altitude profile is determined by the cruise altitude and several step altitudes.
a Predictions
_ Cruise predictions are based on the aircraft flying level at the cruise altitude using the appropriate thrust to maintain: the optimum cruise speed. If step climbs or descents exist in the F-PLN, they are taken into account in the cruise predictions. They are assumed to be flown maintaining step speeds and:
-
for step - descents: - 1000 ft/mn
-
for step - climbs: Max climb thrust.
b Guidance
_
-guidance mode requested by the FM part ALT is the normal guidance mode. But if there is a step-climb (or descent) inserted into the flight plan, CLB (or DES) mode is requested when the step point is sequenced
-if ALT ACQ or ALT mode is active, the speed target is the ECON cruise speed
-when CLB or DES mode is active, the requested submodes and their associated targets may be (in accordance with predictions):
CLIMB - Before Speed Limit Altitude
Figure 013
CLIMB - Passage of Speed Limit Altitude
Figure 014
R Leveling off Due to Altitude Constraint (Sheet 1/2) Figure 015
R 1EFF : 106-149, 151-199, 211-299, 301-399, 1 22-73-00Page 27 1401-499, 1Config-2 Aug 01/05 1 1 1CES 1
R Leveling off Due to Altitude Constraint (Sheet 2/2) Figure 016
R 1EFF : 106-149, 151-199, 211-299, 301-399, 1 22-73-00Page 28 1401-499, 1Config-2 Aug 01/05 1 1 1CES 1 ---------------------------------------------------| | CLIMB mode | DESCENT mode | |----------|------------------|-------------------| | Elevator | SPD | V/S | | Target | ECON step speed | - 1000 ft/mn | |----------|------------------|-------------------| | Thrust | THR | SPD | | Target | Max thrust | ECON step speed | ---------------------------------------------------
-if the A/C is still in cruise beyond T/D, the message DECELERATE is displayed on the PFD. (Ref. Fig. 017)
4 Descent
_
a Descent parameters
_ In order to improve the prediction and guidance along the flight plan for descent and approach phases, the pilot has to insert some meteorological data during cruise on the APPR and DESCENT WIND pages. These data are the following:
-destination temperature
-descent winds (including destination wind)
-destination QNH which is used to convert flight levels
into altitudes and vice versa for descent profile. At 180 NM from destination, a message ENTER DEST DATA is displayed on the MCDU as long as these data are not inserted. (Ref. Fig. 018)
b Theoretical descent profile
_ Predictions and guidance for descent phase are based on a computed theoretical descent profile. This descent profile is defined by a series of geometric altitude and speed targets which are functions of the distance to the destination. It is computed backwards from the Decel point (for definition of Decel, Ref. approach phase) up to the cruise level taking all descent constraints into account. In case of conflict into altitude constraints, priority is given to higher constraint. The descent path consists of two or three parts: the geometric path, the idle path and if requested by the pilot, a repressurization segment. It does not take holding pattern (HM leg) into account.
-Geometric path
Step Climb in Cruise phase
Figure 017
Display of Descent Parameters
Figure 018
If a path based on hold of idle thrust and ECON speed does not enable satisfying some altitude constraints, a geometric path composed of constant- slope segments is constructed from the Decel point up to the highest restrictive altitude constraint (it may therefore not exist). Predicted speeds on geometric path are based upon knowing an initial ending speed (at the DECEL point) and then progressing backwards through the F-PLN. The method of obtaining the speed changes is based upon integrating up the segments assuming idle thrust. The method of obtaining the speed hold is based upon integrating up the descent path assuming the segment control on elevator and the speed hold on thrust.
But the slope of a segment may be too steep either to maintain a speed or to get a speed change even assuming speedbrakes extended to mid travel. In that case, a vertical discontinuity is created and the message TOO STEEP PATH AHEAD is displayed on the MCDU to warn the crew before entering the descent phase or the too steep segment (if already in descent). The construction of the profile re-starts from the next constraint point.
-Idle path Above the higher restrictive altitude constraint (named GPP, Geometric Path Point), an idle path is created up to cruise flight level or in case of recomputation during descent, until A/C position. It is based on hold of Econ descent speed and idle thrust
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：A320飞机维护手册 AMM AUTO FLIGHT 自动飞行4(7)
