What are the IDLE / PERF Factors in Airbus A320? – THE AVIATION
What are the IDLE / PERF Factors?
The FMGS (Flight Management and Guidance System) contains a database that aids in predicting aircraft performance and calculating necessary data. However, variations in aircraft configurations can lead to discrepancies between the database information and the aircraft’s actual performance. To address this, the FMGS applies corrections to its computations.
The FMGS contains a performance database to compute the predictions and the performance data. This performance database has a model of several aircraft configurations (aircraft type/engine model) to tune the performance and the FMGS predictions.
For some aircraft configurations, the model can differ from the real aircraft performance. In these cases, the FMGS has to correct the computation of the performance and the predictions. This is the aim of PERF and IDLE factors. With time, the real aircraft drag and engine performance can deviate from the nominal model.
It is Prime Responsibility of The airline Flight Operations should periodically revise the value of these factors to adapt FMGS predictions to actual aircraft performance. Kindly Note: The IDLE factor is not available on aircraft with #FMS1 Honeywell Legacy.
Over time, factors such as aircraft drag and engine performance may deviate from the database’s baseline figures. This necessitates periodic adjustments to ensure accurate performance predictions.
What is PERF Factor:
The PERF factor is used by the FMGS to adjust the predicted fuel consumption. For example, if the PERF factor is set to +1.8, it indicates that the aircraft’s fuel consumption is 1.8% higher than the baseline performance model. Typically, older aircraft require more significant corrections.
What is IDLE Factor:
The IDLE factor is used to fine-tune the aircraft’s vertical profile during descent, specifically from the Top of Descent (TOD) to the first altitude constraint. It modifies the idle thrust by adding a delta thrust, allowing the aircraft to maintain the computed vertical profile despite unexpected wind conditions.
1.A positive IDLE factor results in a less steep descent profile, causing the descent to begin earlier.
2.A negative IDLE factor makes the descent profile steeper, leading to a later start of the descent.
These adjustments ensure the aircraft follows an optimal descent path.
PERF Factors
Takeoff and Landing Performance Calculations:
Weight Limits: Calculate maximum takeoff and landing weights based on runway length, altitude, and temperature.
Thrust Settings: Determine thrust settings for takeoff (usually TOGA) and approach (typically reduced thrust).
Performance Charts:
Utilize performance charts in the Aircraft Flight Manual (AFM) to find required distances for takeoff and landing based on various factors (weight, flap settings, wind).
Procedures:
Pilots will go through pre-flight calculations for performance data, adjusting settings based on environmental conditions (like temperature and wind).
General Procedures
Before Takeoff: Calculate required thrust, confirm takeoff speeds (V1, VR, V2), and configure flaps.
During Approach: Monitor descent rate, configure for landing (flaps, gear), and verify landing speeds based on current weight.
IDLE PERF default setting – Airbus A320 Neo
MCDU A/C STATUS IDLE/PERF data entry?
THR IDLE/SPEED modes in descent – Flight Factor
