IDLE AND PERF FACTORS: A CONTROLLED PREDICTION STUDY
Fenix V3 documents user-adjustable IDLE and PERF factors for descent characteristics and fuel predictions. The supplied Thales material shows the combined IDLE/PERF reference and percentage-format conventions. These are model-adjustment inputs, separate from cost index, cruise level, reserve policy and actual fuel quantity. Before changing them, establish a consistent baseline flight and a specific observed prediction discrepancy to investigate. [66, PDF pp. 94,465,669-670] [82]
1. Record the baseline. Note airframe/engine, current factors, mass, active route, cruise reference, forecast winds, configuration and relevant build/platform. Capture the predicted T/D and destination time/fuel before the study. If comparing with an actual flown sector, record relevant mode, speed and configuration changes too. A descent flown on vectors with substantial speed intervention is not directly comparable with a different uninterrupted managed-profile prediction. [66, PDF pp. 94,465,669-670] [82]
2. Resolve ordinary data errors first. Recheck route geometry, altitude/speed restrictions, mass/fuel, weather and the actual speed schedule. A bad alternate route can corrupt reserve/extra interpretation; an incorrect wind layer can move descent timing. Changing a factor to compensate can make one result look better while leaving the underlying flight wrong. Retain normal settings unless a justified controlled study or applicable guidance calls for adjustment. [66, PDF pp. 94,465,669-670] [82]
3. Identify the actual field and order. Read the loaded A/C STATUS or supported interface rather than assuming every old combined-field layout is unchanged. The source uses IDLE/PERF and signed percentage-style inputs; verify the individual members and accepted values after any permitted entry. Do not guess a change-code sequence, hidden binding or crossload procedure to expose a field that is unavailable. [66, PDF pp. 94,465,669-670] [82]
4. Change one justified input at a time. Within the documented current facility, make only the intended factor adjustment and re-run a comparable study. Record the changed prediction and observed effect. This chapter supplies no preferred numerical correction or universal positive/negative rule for every aircraft standard. Establish the implementation's actual effect instead of importing a setting recommended for another engine, simulator build or flight model. [66, PDF pp. 94,465,669-670] [82]
5. Preserve a reproducible result. Compare like-for-like route, atmosphere, mass and speed conditions, then retain or restore settings deliberately. A factor change is not evidence that a known prediction bug has been fixed and does not alter runway-performance requirements. The useful PRO outcome is an explained relationship between a documented input and a repeatable result, with the ordinary preparation still valid and the original baseline available. [66, PDF pp. 94,465,669-670] [82]