8.6 Fuel Freezing Limitations
8.6.1 The minimum allowed fuel temperature may either be limited by:
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The fuel freezing point to prevent fuel lines and filters from becoming blocked by waxy fuel (variable with the fuel being used), or
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The limitations of the engine fuel heat management system.
8.6.2 Different fuel types having variable freezing points may be used as mentioned in the FCOM. When the actual freezing point of the fuel being used is unknown, the limitation is given by the minimum fuel specification values. In addition, a margin for the engine is sometimes required.
8.6.3 The resulting limitation may be penalizing under certain temperature conditions especially when JET A is used (maximum freezing point -40°C). In such cases, knowledge of the actual freezing point of the fuel being used generally provides a large operational benefit as surveys have shown a significant giveaway.
8.6.4 Although the fuel freezing limitation should not be deliberately exceeded, it should be known that it ensures a significant safety margin.
8.6.5 When mixing fuel types, operators should set their own rules with regard to the resulting freezing point, as it is not really possible to predict it. When a mixture of JET A/JET A1 contains less than 10% of JET A, considering the whole fuel as JET A1, with respect to the freezing point, is considered to be a pragmatic approach when associated with recommended fuel transfer.
Issue II 02.07.2009 Rev. 0
8.7 Low Temperature Effect on Altimetry
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Altimeters are calibrated to indicate true altitude under ISA conditions. Any deviation from ISA will therefore result in an erroneous reading on the altimeter.
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In the case when the temperature is higher than ISA the true altitude will be higher than the figure indicated by the altimeter; and the true altitude will be lower when the temperature is lower than ISA. The altimeter error may be significant under conditions of extremely cold temperatures.
Altimeter correction tables for low temperatures are placed at Appendix – ‘C’. The crew must correct charted altitudes for potential errors in altimetry.
Issue II 02.07.2009 Rev. 0
CHECKS TO DETERMINE THE NEED TO DE-ICE/ANTI-ICE
9.1 Forecast / Present Weather Conditions
The ability to obtain and understand prevailing and forecast weather conditions is of great importance to operations staff as they plan on-going operations. Weather conditions dictate whether the aircraft needs to be de/anti-iced on the ground. For this purpose, they need to continuously monitor weather and the future trends to take effective steps to de/anti-ice the aircraft well in time.
9.2 Clean Aircraft
Aircraft preparation for service begins and ends with a thorough inspection of the aircraft exterior. The aircraft, and especially its surfaces providing lift, controllability and stability, must be aerodynamically clean. Otherwise, safe operation is not possible.
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