Here's how it works -- and bear with us as we get a bit technical:
Currently, there are two possible flight statuses regarding the ash cloud. First there's the No Fly Zone; in this case, ash is too dense to allow flights through and airports close. Then there's the Enhanced Procedures Zone; flights are permitted but planes must receive extra inspection. Now that it's been determined that airplanes can safely fly through medium-density ash clouds for a limited time, a third option has been introduced between the two: the Time Limited Zone. This effectively doubles the levels of ash deemed safe for airlines to fly through.
The new measures are the result of research and analysis conducted since the Eyjafjallajoekull volcano began erupting in mid-April. The zone will go into effect tomorrow (Tuesday, May 18). Ultimately, the result should be fewer airport closures or canceled flights that could disrupt summer travel plans while a high level of aircraft safety is maintained. However, airlines must apply to use it by presenting CAA with an argument of why it will be safe for their planes to fly, based on green lights given by the aircraft and engine manufacturers.
--by Erica Silverstein, Senior Editor
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