Are winglets worth it?

摘要

Despite all of the numbers involved, fleet planning is an imprecise science. It is often said that fleet planners do not know whether or not they made the right decision until decades after they made it. The reason is that many of the assumptions necessary to evaluate quantitatively alternative aircraft types can be characterized as educated guesses about issues such as economic growth, cargo yields and fuel costs over a new aircraft's 30-year-plus service life. In such an uncertain analytical environment, market conditions and emotional factors ― such as loyalty to a particular airframe manufacturer ― can unduly sway decisions. A number of all-cargo carriers decided to acquire new freighter aircraft, such as the 747-400F and the MD-11F, in the second half of the 1990s, when the world economy was buoyant and the supply of older widebody aircraft was relatively tight. Yet, typically, the new aircraft began to arrive as the record-setting economic boom was running out of steam, putting downward pressure on air cargo traffic and yields.