To answer ANCDU's query.
The data that airlines are getting on the location and the height of the Volcanic Ash "no-go" areas are produced from the Darwin VAAC (Volcanic Ash Advisory Centre) for an area from the middle of the Indian Ocean to 160E (approximately the middle of the Tasman Sea). Wellington VAAC has its responsibility from the 160E Longitude to close to the South American Coast. The next VAAC if you head beyond the Wellington VAAC Area is Buenos Aires. The Northern Hemisphere has similar arrangements, London Toulouse, Washington, etc.
I have flown across the Tasman Sea betwen NZ and Australia several times when the Darwin Charts had 3 types of areas defined in Altitude bands. At the same time the Wellington Charts had two. We were rerouted from the normal relatively "straight lines" tracks that are the air routes between NZ and the east coast cities of Australia to avoid flying into the lowest altitude band and flew in an area where the "floor" of the Area was at FL280 at FL250. Similarly a crossing was made at FL220 when the "floor" was at FL250.
Yesterday the Darwin Charts had two "Altitude Bands" and the Wellington chart had only one with "floor" over a significant part of its area at FL180 so the final part of a flight from North Asia into Auckland was completed at FL150. Others flying in the different quadrantal were at FL160.
Flying low and by circuituous routes has a significant economic impact on the operation, descent was made north of Norfolk Island from FL370, fuel flows increased by the order of 15% per hour however the real killer was the reduction in air speed from a TAS of 485 to 365 thus adding a further 28 minutes to the flight time as compared to normal flight at FL370 then descent to land as opposed to FL370, descend to FL150, cruise for approximately 95 mins at this level then descend to land.
The lower limits of the Oceanic CTAs have also been adjusted downwards to keep these lower altitudes still within controlled airspace.
Last edited by ghw78; 28th Jun 2011 at 05:31.