Wall Street Journal had several articles on Continental Airlines flights to the East Coast from Europe that have been forced to make unexpected stops in Canada (and smaller airports on the east coast) to fill up their fuel after running into unusually strong headwinds. (“Nonstop Flights Stop for Fuel“, and “With Few Options, Continental Could Add Extra Tanks“) The stops are partly the result of a decision by United to use smaller jets on a number of long, trans-Atlantic routes.
United’s strategy works when the winds are calm, and it allows the airline to operate less expensive aircraft with fewer cabin-crew members to an array of European cities that wouldn’t generate enough traffic to justify larger planes. But by pushing its international Boeing Co. 757s to nearly the limit of their roughly 4,000-nautical-mile range, United is leaving little room for error when stiff winds increase the amount of fuel the planes’ twin engines burn.
This is an interesting and classical problem in operations. The firm needs to decide which plane to allocate to which route. Take for example routes to less popular European cities. The airline can choose a relatively small plane, ensuring high seat utilization, and the ability to charge a relatively high price per seat, but exposing itself to the risk of running out of fuel when flights take longer than expected, and the costly implication of angry customers, long delays, and missed connections. The airlines can also choose a larger plane with clear benefits and disadvantages. When determining the exact allocation of planes to routes, the weather and winds are not known, and thus one has to account for the different possible scenarios and the associated consequences. From reading the article we learn that last month, United’s 757s had to stop 43 times to refuel out of nearly 1,100 flights headed to the U.S. A year earlier, there were only 12 unscheduled stops on roughly the same volume of 757 flights. Which means, that this is not a very rare event. We also learn that this year’s likelihood of such an event has gone up by an order of 4. At what ratio will the cost dominate the benefits? Even if it happens with this likelihood, it does not mean that this is a bad decision. It is clearly a PR disaster, but I am not sure that it is an operational one. This problem is not identical to the newsvendor problem, but it’s pretty close.
We should note however, that the airline could affect the likelihood of running out of fuel by trying to increase the amount of fuel or reduce the weight, and thus increase the range.
Gordon Bethune, a former Boeing executive who went on to become Continental’s chief executive and retired in 2004, said Wednesday that the airline talked to Boeing about installing extra fuel tanks in the bellies of the aircraft. “But you give up a lot of luggage space and it’s not economical,” he said. “And it’s fairly complicated.”
Again, it’s all about tradeoffs. A very related problem is faced by the FAA, which has been struggling to approve the 757 for the longer routes.
“The report did note that some controllers and a pilot-union safety official “expressed concerns regarding the use of Boeing 757s on long, overseas routes,” particularly when westbound flights from Europe ended at congested airports in the Northeast.”
As a United customer myself, I am quite sure to start formulating my own decision tree, and adding this issue to the on-time-performance I already account to.