The two alpha
Mach indicators are located next to the attitude director indicators
on panels F6 and F8. The AMIs consists of four tape meters displaying
angle of attack ( alpha ), vehicle acceleration (accel), vehicle
velocity ( M/vel ) and equivalent airspeed ( EAS ). The two units
are driven independently but can have the same data source.
vehicle angle of attack, defined as the angle between the vehicle
plus X axis and the wind-relative velocity vector (negative wind
vector). Alpha is displayed by a combination moving scale and moving
pointer. For angles between minus 4 degrees and plus 28 degrees,
the scale remains stationary and the pointer moves to the correct
reading. For angles less than minus 4 degrees or greater than plus
28 degrees, the pointer stops (at minus 4 or plus 28 degrees) and
the scale moves so that the correct reading is adjacent to the pointer.
The alpha tape ranges from minus 18 to plus 60 degrees with no scale
changes. The negative scale numbers (below zero) have no minus signs;
the actual tape has black markings on a white background on the
negative side and white markings on a black background on the positive
The accel scale
displays vehicle drag acceleration, which is the deceleration along
the flight path. This is a moving tape upon which acceleration is
read at the fixed lubber line. The tape range is minus 50 to plus
100 with a scale change at zero feet per second squared. Minus signs
are assumed on the accel scale also; the negative region has a black
background and the positive side has a white background.
The M/vel scale
displays Mach number or relative velocity. Mach number is the ratio
of vehicle airspeed to the speed of sound in the same medium. Relative
velocity in this case is the vehicle airspeed. The actual parameter
displayed is always Mach number; the tape is simply rescaled above
Mach 4 to read relative velocity in thousands of feet per second
(above 2,000 feet per second, Mach number = V REL /1,000). The M/vel
scale is a moving tape from which Mach/velocity is read at the fixed
lubber line. The scale ranges from zero to 27 with a scale change
at Mach 4.
The EAS scale
is used to display equivalent airspeed. On the moving-tape scale,
equivalent airspeed is read at the fixed lubber line. The tape range
is zero to 500 knots, and scaling is 1 inch per 10 knots.
on the AMI displays an off flag if the indicator malfunctions, invalid
data are received at the DDU or a power failure occurs (all flags
The air data
source select switch on panel F6 for the commander and panel F8
for the pilot determines the source of data for the AMI and altitude/vertical
velocity indicator. The nav position of the air data switch ensures
that the alpha , Mach and EAS on the AMI are the same parameters
sent to guidance, flight control, navigation and other software
users; accel comes from navigation software.
The left, right
position of the air data switch selects predetermined data from
the left or right air data probe assembly after deployment of the
left and right air data probes at Mach 3 for alpha, M/vel and EAS
display. Accel is always derived from navigation software during
entry. It is driven to zero during terminal area energy management
and approach and landing.