Northbeach,
I think you are right about a button on the control column to turn the HUD off. Having to take your hands off the controls to move the HUD isnt ideal, but I guess I am used to doing it. I think your idea makes more sense, and it would be easy to have a button for it. On my type there is already a button on the yoke that brings up a PFD on the HDD, though this doesnt turn the HUD off.
Cyclone,
I think you are probably right re cost. Its cheapest to not have a HUD, next cheapest is 1 HUD, 2 HUD most expensive.
As for different scans, surely if you are only using the HUD for the approach you are having to use a different scan all the time? Wouldnt it be better to only use the HUD and therefore the 1 scan?
On my type a HUD failure doesnt ground the aircraft. 1 failure means the other pilot flies with their HUD while the pilot with the failed HUD goes back to the old HDD PFD. Both HUDs failing just means both pilots use their HDD PFD like they would in a normal aircraft.
Interesting what you say re ideas coming down from the military, this has typically been the way things have happened. With regard to the use of a HUD I think this is still the case, but in terms of technology I think it is the civ manufacturers that are leading the way, with Gulfstream and its EVS being a prime example. They are doing stuff now that is really advancing aviation at a fast rate. Allowing a DH to be reduced using internal visual aids is pretty impressive.
Cheers for the replies so far guys. Interested to hear from any of the guys flying with EVS if possible?