One is heavy maintenance of aircraft, work that many airlines prefer to farm out to subcontractors.

A Government license is not always required, but most airlines prefer it.

Deregulation and increased competition internationally have meant that many airlines prefer to lease costly new planes rather than buy them.

In theory, that might limit the number of planes available to the air fleet, since the airlines might prefer to fill them with civilian passengers.

The airlines would prefer to merge, but laws rule out that simple option.

The airline prefers the runway, if wind direction allows, because it is nearly three miles long.

Mr. Bronner said the airline would prefer that the unions cooperate in its efforts to cut costs.

Of course, the airlines would prefer to avoid bankruptcy court, having had ample experience in it.

The problem, he said, is that airlines prefer to expand service in cities where they already dominate the market, rather than competing for new territory.

Boeing first proposed it in 2001, but airlines generally preferred lower operating costs over higher speed.