(Kirk Stant) wrote in message

And it seems the military and airlines agree - all big
glass displays and HUDs use ditigal displays, with perhaps a dial for
trend only. I think those studies were all done in pre-digital days,
when the options were a lot more limited.

The CRT and LCD displays used in modern transport aircraft cockpits
allow the display of data in almost any format. Engineer's creativity
is usually limited by conservative certification authorities. In
almost all cases the primary flight display presents altitude and
airspeed as moving vertical tapes with a digital readout included in
the index. Glass cockpit 737 displays software provides an option to
display all instruments as conventional "steam guages". Only one 737
customer bought that option and it was to maintain commonality with
old 737's. Business jet and transport aircraft Head up Displays also
show airspeed and altitude as vertical tapes but may have a declutter
mode that removes the tapes and leaves only the precision digital
index.

Engine indications on most systems I have worked on are round dials
with a digital readout in the center. Vertical tape engine indicators
were selected by a small number of customers.

Round dials with pointers give a good indication that a parameter has
fallen outside a narrow allowed operating range but that is not
applicable to altitude and airspeed that have very large normal
operating ranges.

I have a 57mm winter altimeter and a 302. I look at the 302 altitude
first and back it up with the Winter which is harder to read.

Andy (GY)