Following a discussion in another thread (
http://www.pprune.org/forums/showthr...#post3481068):
There are a few airways over the Channel with base FL35, while the transition altitude is 3000 feet. In a situation with low air pressure, FL35 may well be below 3000 feet.
According to my Air Law book, flight levels always start above the transition altitude. With low pressure, FL35 therefore may not exist. At the very least, it is not available for flying.
But what happens to the airway if the base is defined as FL35? Will the base really, formally, legally, drop below the transition altitude of 3000 feet? It would be more logical (and safer) if the base would never be lower than the transition altitude. Plus, the lowest flight level in that airway is not available anyway, so who would care?
My air law book doesn't give an answer. Anybody else knows the details?