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All of these could lead to an aircraft not flying straight in cruise with all lateral / directional control surfaces in perfectly neutral positions.
On A310/A300-600 aircraft, Airbus recommends to laterally trim an asymmetrical aircraft with the zero control wheel technique because it is less fuel consuming than any other technique.
On fly-by-wire aircraft, the flight control system compensates almost 100% for changes of trim due to changes in speed and configuration. Changes in thrust result in higher changes in trim and are compensated for by changing the aircraft attitude.
The apparent drag, resulting from a lateral asymmetry of the aircraft will bias cruise performance analysis. On A310/A300-600, an aircraft lateral asymmetry can result in a 0.3% deterioration of the specific range.
Procedures for checking the aircraft lateral symmetry are given in the Flight Crew Operating Manual: -In section 2.02.09 for A310 and A300-600 aircraft types -In section 3.04.27 for fly-by-wire aircraft
3.4.1.4. Bleed and pressurization (BIAS)
Cabin air leakage may result in increased engine bleed extraction (for the same thrust) and aerodynamic flow losses. This is most of the time of second order influence but in some cases it should be closely monitored and carefully corrected (whenever possible) so as to decrease the bias on the analysis.
Selecting anti-ice and measuring cruise performance can also give a useful comparison with anti-ice off. The nominal extra fuel consumption at flight
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring

BACKGROUND
conditions can be calculated from the IFP and can be compared with the measured difference in fuel consumption / SR with and without anti-ice. For those cases where this measured difference is below the nominal difference, it can be hypothesized that some bleed leaks in the anti-ice ducts may be at the origin of engine fuel flow deviation with anti-ice off. This test is performed for qualitative purposes only, and suggests the possibility of leaks without necessarily estimating the extent or amount of actual engine deviation.
For the purpose of performance monitoring, Airbus recommendations are to fly in as stabilized conditions as possible. In particular, the bleed configuration should be as follows to have the data collected:
- anti ice OFF -air conditioning NORM Additionally, asymmetrical bleed configuration must be avoided to get relevant data for analysis. In case of asymmetrical bleed configuration, no data is automatically recorded via the Data Management Unit (DMU) or via the Flight Data Interface and Management Unit (FDIMU).

3.4.2. Environmental factors
Weather is one natural phenomenon that man has not yet learnt to reliably predict, although accuracy is really increasing. Weather has of a critical influence on aircraft performance and on the outcome of the flight operations.
The intent of the following is to describe potential factors often encountered and may have a significant effect on cruise performance analysis in terms of scatter.
　
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