McDonnell Douglas A-4E Skyhawk, Руководство пользователя

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7. Sensors
AN/APG-53A Radar System
TERRAIN CLEARANCE - PROFILE MODE
The LONG-SHORT range switch provides either
20- or 10-mile ranges for sufficient detail under
various conditions. Vertical marks on the horizontal
zero-degree elevation line divide the display into 2-
or 4-mile segments according to the range in use.
A flag-type marker in the aircraft silhouette at the
left of the scope shows which range is in use.
A solid line representing an imaginary plane 1000
feet below the antenna zero-degree elevation line
is electronically displayed on the indicator as an aid
to low level navigation. This is the terrain clearance
scribe line (see figure 1-20) and is synchronized
with the elevation sweep. The zero-degree
elevation line of the indicator reticle represents the
instantaneous forward projection of the aircraft
flight or armament datum line depending on the
position of the angle-of-attack switch. Since the
vertical calibration is in degrees of antenna
depression angle rather than in feet of altitude, the
resulting expansion of the conical radiation pattern
into a rectangular display causes the 1000-foot
marker and radar target return to curve downward
at the low range end of the indicator. (See diagram
later)