There are lots of rationalisations for corporate aircraft, but the main driver is 'does the boss really want one?'.
Yes, it makes all the sense in the world for Ford or GM or Airbus to run milkruns around their European plants, but never forget the old, and reliable, rules of investing:
IF: your company has a Queen's Award to Industry flag on the front lawn.
IF: Your CEO is on a Government Committee.
IF: Your CEO has received an award such as 'businessman of the year'
IF: Your Company uses corporate aircraft.
For God's sake........SELL the shares!