A Complete Manual for Conducting International Flight Operations
Winds & Temperature Entry
Navigation System Flight Plan Winds and Temperature Entry
Once the flight plan has been entered into the FMS, it very important to review the winds and temperatures for the flight. This provides for a last opportunity to determine that the aircraft’s altitude capability and fuel load are sufficient prior to flight.
With respect to temperatures when crossing the North Atlantic, temperatures may be significantly above ISA. This is due to the tropopause being lower (altitude) the closer you get to the earth’s poles. The tropopause is lower because it receives less radiant heat from the sun, and therefore less convection occurs. What this means to you as a pilot is that if you carry fuel based upon a normal cruise altitude of FL400, you may find yourself in flight and only capable of flying at FL340. If you are flying in the area of the tracks, you may be prevented from climbing to your desired flight planned altitude and may become fuel critical at a time when there are few divert options. The example to the right indicates temperatures as high as ISA +17 at altitude.
In evaluating the Challenger 604’s performance and altitude capability, the ISA +20 table is used. It is advisable to always use higher, hotter, heavier charts to obtain the most conservative performance estimates.
In reviewing this table, a weight below 48,000 lbs is required prior to climbing to FL370 and a weight of less than 44,000 lbs is required prior to climbing to FL390. If a flight crew made the mistake of accepting FL390 in the initial climb, the aircraft will certainly exceed its capability when it encounters ISA +17 temperatures only 45 minutes into the flight.
Entering Flight Planned Winds
By the same token, entering the flight planned winds allows crewmembers to double check the accuracy of the flight plan. Most FMS computers today have the ability to enter winds and temperatures at each fix, or to upload winds via satcom and to produce very accurate fuel burns and time estimates. The shortcut of entering a composite FMS wind should be avoided in the FMS initialization because when plotting, a greater degree of accuracy is required. Controllers will ask for estimates for ETA’s at the destination as well as fixes that may be thousands of miles away. Having accurate FMS winds will also assist crewmembers in departing in a timely fashion when a slot time exists at the destination.
Revision date: July 29, 2015
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