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The variation in traffic between the weeks in February is the smallest. Week 6 traffic is below February average.

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Week 15 in April appears as the lowest traffic week of the month.

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Week 24 in June has the closest traffic value to the average.

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Week 37 in September is the lowest traffic week of the month (11th of September events).

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Week 41 and 49 are both respectively above October and December averages.

This graph shows the difficulty in planning ahead how representative will be the choice made for collecting data. The same graph was made once 2002 CFMU data were published and are shown in Figure 29. Globally the same trend can be observed except an increase of flights in September 2002:

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The same comments apply to weeks 6 and 15 in 2001 and 2002.

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Week 24 has a higher traffic than the average.

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Week 37 has the highest traffic of the month.

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Weeks 41 and 49 have the closest traffic value to their respective averages.

Figure 27: Evolution of the Traffic in the CFMU area. (Source: CFMU, 2002).

2.1.2. Selection of the key month in the US area

Finding equivalent source to European data in the USA revealed difficult. Data expressed in terms of number of flights were published by the US Department of Transportation but mentioned traffic between the US and the world. Other sources as the Air Transport Association publishes data expressed in Revenue Passenger Miles, Revenue Passenger Enplanements, Available Seat Miles or Passenger Load Factor but not in terms of number of flights.
The analysis of monthly traffic was then based on data published by the US Department of Transportation for 1999 and 2000. These data includes all traffic arriving at U.S. airports and departing from U.S airports on non-stop commercial international flights. Figure 30 illustrates these numbers. It can be noticed that both years show the same trend. February is the lowest season and December traffic is busier than in January. Traffic in March, April, May and June is quite constant. July and August are the months showing the highest traffic. A decrease is observed in September after which the traffic remains fairly constant until December.
The monthly traffic expressed as a percentage of the annual traffic varies between 7 and 9 % (Table 42). For both years, some groupings could be done: 
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January and February.

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March, April, May and June.

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July and August.

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September, October, November and December.

Combining this information with the selection of the months for the ECAC area (i.e. February, April, June, September, October and December) led to an agreement on the months already selected. 
Figure 30: Non-stop travel between the US and the World (Number of departure flight) (Source: US Department of Transportation, 2001).

Table 42: Number of flights traveling between the US and the World in 1999 and 2000 expressed in percent of the annual traffic (Source: US Department of Transportation, 2001).
 1999  1999  2000  2000 
Number of flights  %  Number of flights  % 
January  91865  8.24  93013  7.84 
February  82765  7.42  88241  7.44 
March  94097  8.44  97218  8.20 
April  91333  8.19  95283  8.03 
May  93266  8.37  98953  8.34 
June  93379  8.38  97716  8.24 
July  99218  8.90  108436  9.14 
August  99300  8.91  106976  9.02 
September  91423  8.20  99610  8.40 
　
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