Airspeed warning systems

From: (Robert Dorsett)
Date:         20 Jan 93 02:39:35 PST
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The following may be useful to those interested in maximum operating
airspeeds of civil airliners.  The data is derived from published
straight-line performance graphs for the 727-200, and follows the form:
    V = mh + b

where V = Velocity-maximum operating, VMO, in indicated airspeed.
      h = indicated pressure altitude,
      b = translational offset.
The airspeed warning system has two considerations: airspeed and
structural limitations.  

The airspeed warning system has two user-selectable modes, A and B, to 
handle the structural limitation.  Mode B is used when the airplane weighs
more than 172,000 lbs, or has a zero-fuel weight of more than 136,000
lbs.  Mode A is used, otherwise.  In both cases, structural speed limits
are significantly less than airspeed limits.

The 727's airspeed limitations are defined by mach, at 0.88 to 
0.90, depending on configuration.  Airspeed limitations become the 
limiting factor for Mode B over 25,000'.  For Mode A, 20,000'.

When the airplane exceeds VMO, a clacker sounds, until speed is
reduced under VMO again.

Granted, this is just arcane knowledge, but those of you with 
programmable calculators might have some fun with it.

    For Mode A:
        h =[0,10000)
            m = 0.0016
            b = 380
        h = [10000,21000)
            m = 0.0012727
            b = 383.273
        h = [21000,41000]
            m = -0.00675
            b = 538.75
    For Mode B:
        h = [0,25000)
            m = 0.0008
            b = 350.0
        h = [25000,41000]
            m = -0.00675
            b = 538.75

Robert Dorsett