Salon’s “Ask the Pilot” has some interesting information. A sample:
I’ve been asked why flights headed beyond Europe simply cannot overfly the cloud, since it reportedly tops out at around 35,000 feet, well below the ceilings of most commercial planes. One problem here is that a flight always must be able to descend to 10,000 feet in the event of a pressurization failure. This is true even when flying over high mountains; there is always an escape route that will allow for descent in a relatively short amount of time.
Another question I’m getting is why, flying between the U.S. and Europe, planes cannot circumvent the cloud by taking a southerly track across the ocean? The problem with this is mostly one of fuel capacity. Such a routing would be a lot longer in terms of miles, meaning longer flight times and probable payload restrictions. The reason commercial planes trace a northerly route between the U.S. and Europe, passing along the Canadian Maritimes, Newfoundland, and the U.K., is because that’s the shortest distance — a so-called great circle route. Going straight across the ocean between, say, New York and Rome, is considerably longer.
It’s always fascinating (to me at least) to get a piece of string and a globe and stretch the string the shortest distance between two points. Round objects are funny that way.