RobinsonGO said:
What is the reason why these planes can not fly? Is it because the pilots have low visibility or does it have something to do with ash particulates damaging the engines and/or equipment?
There are a number of potential issues regarding engine contamination with volcanic ash. One occurs where ash builds up on some of the internal parts of the jet engine, specifically the compressor and changes the aerodynamics of that compressor. It is possible, with enough contamination, for the engine to enter a condition called stall and eventually surge where the engine loses power and can also be damaged..
Another problem, is where the turbine cooling holes become blocked. This will cause the turbine blades to increase in temperature and fail, potentially destroying the engine. A further problem area is the combustion systems of the engines which can become clogged and again the engine looses power.
In NZ, because the dust cloud base has been at or above 20,000 ft, Air NZ continued to fly for the past week below 20,000 ft, where jetstar and qantas did not.. In australia, again qantas and jetstart cancelled flights, where Virgin did not.. Same with flights between NZ and AUS, Air NZ flew and Qantas and jetstar didnt.. The main disadvantage for air NZ is it requires more fuel to fly at lower altitudes - so is a greater cost to the airline, it also had to track north into the pacific to be able to get up to curising height, which adds time onto flights and more fuel is used.. So it can also depend on the airline if flights go ahead or not, and cost can be as greater factor as safety in deciding that.
Last night however, the dust cloud came down to 10,000 ft in the southern part of NZ, which then makes it unsafe to fly for large aircraft.. because there is no room for error, not alot of height for recovery if something happens.. Air NZ has now cancelled all large jet flights in the southern part of the south island due to the cloud base dropping..
