(c)
 Optimum altitude The optimum altitude is displayed on the PROG page. It is computed by taking into account the active strategic mode (including the cost index if it is ECON), the predicted aircraft and atmospheric conditions. The optimum altitude is limited from above by first, the maximum altitude (Ref. para 1 above), and then the condition of a minimum of 5 min. flown in cruise at that altitude. (Ref. Fig. 043)

 (8) Maximum Holding Time
 (a)
 Last exit UTC (TLE) If the fix is the TO or FROM waypoint, the FMGC computes the latest time when the A/C has to leave the hold so as to satisfy the fuel reserve requirements (corresponding to EXTRA = 0) and the estimated fuel on board at that time. They are displayed on the HOLD page. (Ref. Fig. 044)

 (b)
 Logic for display of TIME TO EXIT message
 The conditions to display the message are:

 -LAT AUTO CONTROL is active
 -hold is the next or active leg, and it is taken into account for guidance
 -last exit UTC is available
 -and IMM EXIT has not been selected, or RESUME HOLD has been
 selected. Considering: Delta T = Last exit UTC - predicted UTC of next passage over fix Three cases are possible:
 -Delta T > time to fly a complete holding pattern: no message

 Time and Fuel to Exit the Hold
 Figure 044

 -
Delta T < time to fly a 360 deg. turn: message immediately displayed.

 -
Delta T bounded between a 360 deg. turn and a complete holding pattern: message displayed when the A/C next flies the first turn of the holding (1min. after passage over fix.)

 The message, when displayed, is removed if it is cleared by the pilot, if the IMM EXIT prompt is selected, or if LAT AUTO CONTROL is not active.
 (9) Wind/Temperature Model
 (a)
 Wind model If no wind has been inserted or entered by the pilot for climb (descent) at intermediate levels between origin (destination) altitude and cruise altitude, a default climb (descent) wind model must be used for wind prediction . It is defined as follows: Default climb (descent) wind model: The wind is linearly interpolated versus altitude in magnitude between origin (resp. destination) wind and T/C (resp T/D) wind. Winds at origin (resp. destination) and cruise altitude have default values of 0kt. If they are entered by the pilot, wind direction is also linearly interpolated versus altitude ; but if only one entry is made, the wind direction is constant and equal to the entry. If no wind has been entered, no wind direction is defined: 0kt/O deg. is displayed.

 (b)
 Temperature model Temperature predictions along the Flight-Plan are based on standard model (ISA), pilot entries and actual temperature at the present position of the aircraft. Temperature may be entered only at cruise flight level through the INIT A or the FUEL PRED page and at destination through the APPROACH page. (Ref. Fig. 004, 038)

 (10) Secondary F-PLN predictions A secondary F-PLN may include all of the vertical elements possible in the active primary F-PLN, except that climb or descent wind entries are not possible. Performance calculation methods are the same (and use the same performance factor), except that altitude planning (on the SEC PERF pages) is not possible and only MCDU pseudo waypoints are predicted.

 (a)
 Secondary F-PLN created by a copy of active F-PLN Predictions are calculated if:

 1. 1.1- flight phase is preflight and the origin airports are identical (although the selected runways may differ) or 1.2- flight phase is take off, climb or cruise and the first lateral leg of the secondary F-PLN is identical to the active leg of the active F-PLN AND

 2. 2.1- the secondary F-PLN does not include a destination or 2.2- the top of descent pseudo waypoint for both the secondary F-PLN and the active F-PLN are predicted beyond the aircraft If the above conditions are not met, secondary flight plan predictions are dashed. Performance calculation methods for the secondary F-PLN created by COPY ACTIVE are based on the same assumptions as for the primary F-PLN : before engine start the primary INIT data is used (weights, ZFWCG, CRZ FL, etc) ; after engine start, the same current aircraft characteristics (GW, FOB, CG, ALT, SPD, engines running : 2 or 1) and the same CRZ FL, as the primary F-PLN. When any of these data is modified, SEC F-PLN predictions are updated accordingly. No secondary F-PLN predictions are available when engine out mode is active. When available, predictions are provided for display on the following MCDU pages: SEC F-PLN : predictions for each waypoint and pseudo waypoint up to and including the destination ; for the SEC ALTN F-PLN only EFOB at destination is calculated. HM's in the SEC F-PLN will be ignored by predictions until the HM entry fix is sequenced. SEC VERT REV : fuel predictions. SEC PERF : predictions at destination (total time and distance). Altitude planning is not available. Entries of cost index, manual speed preselections, and descent auto speed are taken into account.
　
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