Glass (Re: A320 and a bit on the bloody DC-10)

From:         Robert Dorsett <>
Date:         10 Jul 93 02:01:36 PDT
References:   1 2 3 4
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In article <airliners.1993.503@ohare.Chicago.COM> inc@tc.fluke.COM (Gary Benson) writes:
>In article <airliners.1993.488@ohare.Chicago.COM> writes:

>>>thus far, pilots have been surprisingly good at working around the problems 
>>posed by glass (maybe it does have a benefit--at least in most glassy 
>>airplanes, it keeps 'em on their toes? :-))
>Please, for those among us who only lurk  - - - what is "glass" ?
>I`ve read this any number of times referring to some quality of an
>airliner's cockpit. What does this mean?

Conventional cockpits (since the late 50's) used something called "electro-
mechanical" instrumentation.  These were instruments which used mechanical
means to show information, but often got their source data in the form of
electrical signals sent by transducers in various parts of the airplane.  
There were only a few "conventional" flight instruments, of the form familiar 
to private pilots, with direct link-ups to the pitot/static system, for 
instance.  The only "direct linkup" flight instruments were the backup

In the late 70's, manufacturers began to replace these electromechanical
displays with color cathode ray tubes.  Initially, the CRT's were used for
artificial horizon and HSI information, with electromechanical instruments
"completing the T" (airspeed, altitude, vertical speed).  Then engine 
instrumentation was repaced by CRT's, Flight Management Systems (a new 
service) were integrated, etc.  With the FMS's came more sophisticated 
navigation displays, which could produce a plan view of the airplane's flight 
plan, in addition to a standard "HSI" format.  The 757/767/A310 generation 
were the first major transport aircraft to reach this level.

By the late 80's, there was pressure to eliminate the rest of the electro-
mechanical displays (which deriders referred to as "steam gauge" instruments).
So the airspeed, altitude, and vertical speed data was incorporated into the
artificial horizon CRT (usually called a "Primary Flight Display", also an
"integrated display") and the electromechanical displays were eliminated.
Voila, the current stage of flight instrumentation.

Along with all these changes came different philosophies in how pilots
should fly the airplane (the "manager-of-systems" concept became quite 

When I refer to glass, I'm usually referring to CRT/FMS-based airplanes
which reflect the changes in flight management introduced in the 1980's.
I think this is probably a fairly common interpretation: but it should
be noted that some airplanes, like the 737-200 and -300, have FMS's without 
the glass.  And the use of glass in other categories of airplanes can range
from the very simple (such as a small CRT simply "replacing" an artificial
horizon, with no additional services) to airliner-level complexity.

There were early concerns as to the mechanical reliability of CRT's, but 
these have been mostly groundless: CRT's have been very reliable.  Pilots 
like the "clear" displays, without parallax.  

Pending issues include display design formats, as well as the total inte-
gration qualities of glassy airplanes (i.e., flight displays + engine/system 
monitoring + FMS).  I've also wondered about over-reliance on the quality of 
instrumentation (losing track of the nuts & bolts physical basis for data in 
the face of nicely polished, pretty computer-based results), but I haven't
read anything on this.

Robert Dorsett!!rdd