Originally Posted by
PhlyingRPh
The transatlantic air corridors that aircraft utilize over Newfoundland, the tip of Greenland, Iceland, and Ireland are great circle routes. I understand that the volcanic ash from the Icelandic volcano's is spreading all over northern Europe, but for times when volcanic activity is imminent and there are no ash clouds in the North Atlantic, why couldn't aircraft use a more southerly route?
So, flying from Chicago to London, using a southerly route great circle, one would actually fly from Chicago, south east towards the RDU area, leave the continent off the North Carolina coast and fly closer to Bermuda, the Central Azores and Brest/Normandy before flying over the English Channel to reach London.
The reason the great circle routes exist is because the earth is round - it's quicker to go via the poles.
Aircraft can file a flight plan and fly other routes across the Atlantic, but it becomes problematic when the airspace over your destination airport (i.e. LHR) contains ash dust. i.e. routes like AMS-LON are not even running for this reason.
DL had a flight to FRA the other night that routed ATL to FRA via BDA and over the Azores - this would keep it legal for ETOPS, but aircraft had to turnback to ATL because of volcanic dust over FRA (see DL 14).
Keep in mind this is a widespread event and the ash area is extremely large.
The flights that are operating between the US & Europe are taking a southerly track at the moment, keeping them away from the ash cloud while allowing the flights to operate into airports that are still open (i.e. Spain, Italy, etc).
FWIW, there is a second northern trans-Atlantic track for ETOPS purposes which uses the Azores. A flight from Madrid to JFK, as an example, would typically use such a route. (Azores + Canadian/US seaboard airports keep you within ETOPS)
P.S. southerly "great circle" route would be via the south pole. Remember the earth is a globe & gets wider as it approaches the equator.