2.
Write the new IDLE/PERF factor in the scratchpad

3.
Enter this new factor in line [6L ]. The entered factor is displayed in large CYAN font.

The airline may change the ARM code by modifying the NAV DATA BASE policy file.

2.6.3. A330/A340 aircraft
On the MCDU A/C STATUS page:
1.
Enter ARM into brackets in the CHG CODE line [5L ]

2.
Write the new IDLE/PERF factors

3.
Insert the new factor using [6L] key. A manually entered IDLE/PERF factor is displayed in large CYAN fonts.

2.7. Effects of the PERF FACTOR
Adjusting the PERF FACTOR has an impact on fuel flow predictions. As of a consequence, comparing the scheduled fuel consumption with or without defining a PERF FACTOR will exhibit noticeable differences. The purpose of this paragraph is to succinctly describe the influence of the PERF FACTOR.
First, PERF FACTOR is an FMS internal correction. It is not sent to any other computer linked to the FMS (FADEC, EIU…).
Second, as defined above, the PERF FACTOR basically modifies the FMS predicted fuel flow. Hence, it impacts the items listed below.
2.7.1. Estimated fuel on board (EFOB) and estimated landing weight
The EFOB is calculated based on integration of the predicted fuel flow over time. Thus, the PERF FACTOR has an influence of the EFOB displayed on both MCDU PERF and F-PLN pages.
Also, the estimated landing weight is calculated taking into account the zero fuel weight (ZFW) entered in the MCDU and the EFOB at destination. Consequently, the PERF FACTOR has also an impact on the estimated landing weight at destination.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring

USING THE MONITORED FUEL FACTOR

2.7.2. ECON speed/Mach number
The ECON speeds are calculated so as to minimize the cost function. The cost function depends on the predicted fuel flow or predicted specific range, on the Cost Index entered in the MCDU and on the ground speed.
The PERF FACTOR therefore has an influence on the predicted ECON speeds. The Cost Index used for ECON speeds computation is modified according to the following formula:
CI
CIPF =
PERF FACTOR
1+
100
where CI is the Cost Index entered in the MCDU
CIPF is the corrected Cost Index for the PERF FACTOR
PERF FACTOR is the factor entered in the MCDU
Yet, the influence of the PERF FACTOR is quite small. The highest deviations are generally observed at high gross weights. The effect is more significant on A330/A340 aircraft types.
As a general rule, the higher the PERF FACTOR, the lower the ECON speeds.

2.7.3. Characteristic speeds
The FMS computes flight characteristic speeds and displays the predicted values in the MCDU PERF pages. As a reminder, the characteristic speeds are F, S and O speeds during the T/O and APPR phases, VLS and VAPP CONF3 and CONF FULL during the APPR phase.
　
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