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de Neufville + Scholtes D R A F T September 30, 2009Box 2.4____________________________________________________________________________Difficulty in predicting demand and its componentsForecasts for Boston airport illustrate the difficulty in predicting traffic demand. In the case shownin Table 2.2, the discrepancy between the overall passenger forecast and reality was 10% overonly 5 years. In retrospect, this was due to the burst of the dot.com economic bubble – one ofthose unexpected disruptive trend-breaking events that so frequently and routinely mess upforecasts.The 10% discrepancy was not even across the board however. The number of aircraftoperations dropped by twice as much (23%), as airlines cut out flights by small regional aircraft(42% off the forecast) and squeezed more people into their big jets. This kind of differentialchanges in demand over product categories is typical.[Table 2.2 here]____________________________________________________________________________Box 2.5_____________________________________________________________________________Changing requirements – unmanned aerial vehiclesUnmanned aerial vehicles (UAV) are aircraft that do not carry a pilot. 8 They range in size fromthat of model planes operated by hobbyists to much larger aircraft with wingspans of about 20meters and costing over $8 million each. They differ from earlier drones in that ground operatorsstationed at great distances, often halfway around the world, can tightly control them – the US AirForce has been directing flights over the Middle East from a base in Nevada.UAVs became practical with the development of miniature electronics and globalcommunications. They are thus a product of the 1990s. They thus represent a new technology.Users are gradually understanding how they can best use them.The “requirements” for UAVs have thus been changing dramatically as the users gainexperience with them. Originally, the military imagined them to be surveillance aircraft that wouldloiter slowly over an area. The requirements were therefore for relatively slow vehicles (to make iteasier to get good images) with modest payloads such as cameras and electronic sensors. Morerecently, the requirements for the same vehicles have shifted towards carrying heavy loads (suchas bombs weighing a quarter ton) and greater speeds (to escape anti-aircraft fire). Concurrentlycivilian users, such as the Forest Service interested in spotting fires, have other requirementssuch as those associated with sharing airspace with commercial and other aircraft with people inthem.__________________________________________________________________________Part 1: Chapters 1 to 3 <strong>Page</strong> 36 of 69
de Neufville + Scholtes D R A F T September 30, 2009Box 2.6_____________________________________________________________________________Ten-year traffic projectionsFigure 2.4 shows data for a major airport. As for a number of other major American airports, itstraffic dropped in the late 1990s, in this case by about 20%. This was due to the increasedcompetition from low-cost airlines at secondary airports, and then the burst of the dot.com bubble.The traffic then grew steadily until 2008, when another drop in traffic occurred.The trend we extract from this history depends on the years selected. Suppose wewanted to project ahead 10 years from 2008, and thought it reasonable to look back 10 years forthis purpose. If we consider the period 1998-2008, then we project ahead from about 15 to 18.5,as seen in the graph. However, as has been observed in the past, forecasters might assume thatthe dip in traffic in 2008 was a temporary dip and prefer to prolong the steady trend that seem tohold between 1998 and 2007. Projecting ahead from that period leads to a forecast of over 20.Another defensible view might be that the analysis might best not base a trend from a previouslow to a recent high, and ought to include data from the earlier high. Following this logic to includeall the data from 1996 to 2008, the resulting trend leads to a forecast of about 16.4. As the figuresshow, slightly different assumptions scatter the trends over a range of about plus or minus 10%.Trends are not obvious![Figure 2.4 here]_____________________________________________________________________________Part 1: Chapters 1 to 3 <strong>Page</strong> 37 of 69
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