Even the "benefits" of the mandate above FL290 have been asserted
As far as I can see, this originated in a CASA white paper based on an informal estimate passed in conversation to CASA by one of the airlines. The figure used by CASA in its cost / benefit analysis was 5.5% flight time / fuel saving.
Does anyone really think this smells right?
The really funny thing (if it wasn't so tragic) is that CASA then used this same figure for GA.