This is not an excuse for Jetstar to cancel flights!!!
We have had staff communications today since the cancellations that state it is Qantas policy that flights can't operate 'under' forecast ash cloud which has led to the cancellations for both Qantas and Jetstar. It is an interesting situation as obviously the most safe option is to have aircraft on the ground and not risk a ash cloud encounter. Having said that though, I also wouldn't say that operating at lower altitudes is necessarily unsafe. I guess it comes down to a 'gut call'.
Artifical Horizon,
Yes lets dispense with all manuals and SOP's and operate on "Gut call".
Operations: Sorry due to policy we cannot operate under an ash cloud
Pilot: No worries mate! Its a gut call, I will blast off and operate low level at night over LSALT's above 10,000ft, I know best, she'll be right mate....
Day VMC may be a suitable day to operate under an volcanic ash plume as was the case today. In IMC or at night it may not be best to trust a prediction of how low the ash cloud particles actually are.
Not a nice feeling to get erroneous engine indications and all the other tell tale signs at FL180 at night over the South Island because the prediction was wrong or had changed since the last update.
From my information the affected area changes significantly with each 6 hourly update.
Good luck with the "gut call".