747-400 PFD Airspeed & Mach Indications

[NSEU]

I know this is one of those annoying "what if's" that flightsim programmers sometimes ask, but...

According to my manuals, the 747-400 ADC limits are as follows:

"Airspeed Range 30~450kts
Mach range 0.1 to 1.0
True airspeed (computed from Mach and SAT) 100 to 599 kts
SAT -99 to +60C
.... etc"

What happens when the airspeed and mach parameters are exceeded? For example, if the ADC airspeed limit is exceeded: Does the airspeed tape blank (and the SPD flag appear) or does the tape just hold at 450kts? If the tape blanks, is the mach also removed at this point?

If the ADC Mach limit (i.e. not the Mmo) is exceeded, but not the airspeed, does the digital mach readout disappear (to be replaced with a MACH flag), or does the (optional) Groundspeed display take its place.

The manuals don't specify if the ADC limits are computational limits or ADC databus output limits.

The manuals do say that the SPD flag inhibits the MACH (and other flags), complicating the issue.

Hopefully someone has seen one or more of these scenarios in a sim session.

Thanks.

Cheers
NSEU

[john_tullamarine]

What happens when the airspeed and mach parameters are exceeded?

Somehow I think that my concerns would be elsewhere... rather than worrying about what the gauge does ....

[Long Haul]

Looking at the low end of the scale, when on the ground and not moving the airspeed tape reads 30 without any red lights or flashing. Maybe it does the same at the high end.