1 - The Black Vault

PRAETORIAN STARSHIP
of the command line receded and the bottom face
increased its slope angle (bulges on the E
square), the optimum flight vector could be exceeded
without causing target penetration of the
command line. Thus, a heavy aircraft, one weighing
135,000 pounds and whose optimum flight
vector was 3.8 degrees, would receive, if neces -
sary, a pitch command that could double the optimum
flight vector.
In a dive the command line would react in the
opposite direction. The front-face bulge would literally
drop out and down toward the bottom of the
E squared as if it were eager to meet new video.
Because the display was exponentially scaled, the
grass accelerated as it slid along the zero command
line toward the aircraft.
A satisfactory TFR would maintain terrain
clearances within + or – (10 percent of set clearance
+ 50 feet) over level terrain and at or above
70 percent of set clearance over hilly terrain.
Clearances were checked by radar altimeters, and
substandard performance could normally be identified
visually on the E squared presentation.
Over level terrain the grass would hug the bottom
face of the command line. Grass penetration of
the command line normally occurred during
lower-than-desired terrain clearances, whereas
grass/command line separation was indicative of
higher-than-programmed altitudes. The most
common cause of terrain clearance problems was
found in antenna stabilization. For this reason a
“dual-angle indicator” mounted on the navigator’s
panel was frequently monitored during level portions
of flight to determine the most reliable pitch
angle input.
Occasionally, the aircraft might encounter an
obstacle that it could not clear safely. For that
reason a distinct obstacle warning (OW) zone was
built into the TF template. Any obstacle that
penetrated its parameters would trigger a full fly
up and sound a beeping warning horn. This
would rarely occur on a well-planned route with
the aircraft flying a constant heading. The pilot,
who was monitoring his E squared presentation,
could see the obstacle penetrating the zero command
line prior to its reaching the OW zone.
Most frequent OW alarms were sounded by
other aircraft flying through the OW portion of
the TF scan or by hilly terrain that entered the
OW area sideways during turning maneuvers or
on-course corrections. Whenever an unplanned
OW occurred, an immediate climb command
was displayed on the ADI, and an immediate
corrective evasive action was initiated. Evasive
action included application of maximum climb
power, initiation of a climb, and a turn in the
direction of lower terrain or in the direction provided
by the navigator.
On occasions, TF flight was conducted over
water, snow, sand, and other surfaces that did
not reflect radio frequency energy, including
very smooth and level terrain. Under these con -
ditions radar echoes were of insufficient strength
to produce video and generate necessary climb
commands. To avoid a disastrous dive command
into earth’s surface, the system was programmed
to switch to radar altimeter operation whenever
the TFR commanded a dive below desired clearance
altitude, and there was no visible grass in
the two well-defined altimeter override inhibit
zones located within the template. While operating
on altimeter override, the system’s performance
tolerances were the same as for level
terrain.
The cross-scan mode of operation combined the
features of TA and TF and was the mode most
frequently employed during terrain-following
flights. In this mode the antenna alternated between
horizontal and vertical scans, providing
either TF or TA video to the pilot’s indicator
and TA video to the left navigator’s indicator.
Because of alternating scans, there was a pause
in the TF display during the TA antenna sweep
and visa versa. This video pause did not affect
continuous command input to the pitch bar. To
keep the time interval between successive TF
sweeps at a minimum, the horizontal-scan azimuth
was reduced to + or –20 degrees. Even
though this TA azimuth reduced the coverage of
the normal TA mode by more than one-half, the
compromise gave the left navigator sufficient
sector scan to monitor above flight-level obstacles
during terrain-following operations. TA monitoring
was also available to the pilot who could
select either E squared or TA video by flipping a
toggle switch (fig. 18).
During all TF turns, the scan pattern provided
climb and dive commands based on terrain
that passed laterally across the aircraft’s
nose. Those commands could change rapidly,
with changing terrain profile, from climb to dive
and back again until the aircraft was firmly established
on its new course. For this reason descending
turns were never made during terrain
following. A turn was made either level or
climbing, provided the pitch bar commanded a
climb. A dive command on the pitch bar would be
ignored even when flying over water on altimeter
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