Nick,

I've loaned out my copy of FOTI so I can't immediately refer to it in trying
to answer your question. Try I will, though.

First, the setting for FOTI is the later years of the VN conflict. This is
important because the A-6A was the current Intruder model at that time. The
A-6E had not yet entered fleet service and some of the whistles and bells of
the A system were eliminated or very greatly changed in the E system -
including a couple of terrain-clearance toys that Coonts likely describes in
FOTI.

Second, one must remember that the A-6A was the "first" of its kind - the
first aircraft with full integration of its various sensors into a digital
(not analog, like the Norden bombsight) computer. In this respect it was
also very much "bleeding edge." The personal computing dictum about being
especially wary of Version 1 of anything could as well have been written by
those of us in the A-6A.

Search Radar Terrain Clearance

One terrain clearance toy was a feature called Search Radar Terrain
Clearance (SRTC). As its name implies, SRTC used the A's AN/APQ-92 search
radar to generate a synthetic terrain display on the pilot's Vertical
Display Indicator (VDI), the very large cathode ray tube (CRT) display in
the center of the pilot's console, right under the gunsight. The synthetic
display showed vertical terrain development in a 53 degree by 26 degree
window about the projected flight path. For example, if the Intruder was
heading for a valley between two hills, the pilot would see return generally
in the shape of two hills (one on either side of the display), with a
curving "V" notch in the center between them. (This is somewhat difficult
to describe without a graphic.) The return would slide "down" toward the
bottom of the VDI as the flight progressed and radar return for these
terrain features was processed.

The B/N would not normally monitor the VDI, unless he happened to look over
at the pilot's console. Instead the same radar return was presented on the
B/N's Direct View Indicator (DVI), the CRT in the center of the B/N's
console as a Plan Position Indicator (PPI) information covering an arc of
about 50 degrees and a range of about 27 miles. (A PPI display looks like a
slice of pie whose point is at the bottom of the DVI. The "point" of the
pie slice is where your aircraft is now and the 50 degree arc covers the
terrain ahead of the projected flight path.) PPI information does not give
the crew any indication of terrain elevation so its use alone for terrain
clearance monitoring was not conducive to mission prosecution or crew
longevity. g

By the time I completed type training in the A-6 (1972), we were not using
or receiving significant training with SRTC. The primary reason for this
was
SRTC's inability to detect smaller man-made features - like cables that the
bad guys could suspend across a valley. Every now and then, though, we'd
light up SRTC especially if we were flying a training route like Whidbey's
OB-16 whose features were well-known and for which both crew would establish
a mutually agreeable safety margin. (Humorous example: "300 additional
feet of clearance for each wife, plus 100 additional feet for each kid.")

Elevation Scan

Another feature in the A was Elevation Scan (E-scan). With E-scan the A's
AN/APQ-112 track radar was used to generate vertical terrain development on
the Pilot's Horizontal Display (PHD) the CRT immediately below the VDI on
the pilot's side. The pilot read vertical development "left to right" on
the PHD, with obstructions closer to the aircraft appearing on the left side
of the PHD and those at greater range lying more to the right. (Again, I
apologize. This is hard to describe without a graphic.) E-scan return
would gradually slide from right side of the display (farther away) to the
left (closer) as the flight progressed and new return for the same terrain
was processed. The information displayed on the PHD in E-scan also included
a flight path line and a clearance line. The pilot would scan both the VDI
and the PHD while flying in E-scan mode, performing the necessary spatial
interpretation gymnastics to deduce how close the A was to a possible prang.

The B/N could not observe E-scan on his DVI. His viewing pleasure was
limited to search radar input, usually shown as PPI information while the A
was in E-scan mode.

Like SRTC, E-scan's day had passed by the time I reached type training - if
in fact it ever had a "day" to enjoy. Aside from being a clumsy way of
figuring out how close to pranging you might be, E-scan was further limited
by the track radar's relatively poor reliability.

Hope this helps.

--
Mike Kanze

"Owl", B/N
A-6A, A-6B (PAT ARM), KA-6D


"Nick Coleman" wrote in message
...

Just started re-reading Coont's Flight of the Intruder, and his
description of the capabilities of the terrain radar is interesting.

Early in the book he describes a training flight through canyons and
valleys in IMC, using the radar for avoidance.

I'm curious what the BN would actually see in his scope? Would it be a
like a line drawing of the terrain (quite visual and not needing much
interpretation) or would it be more like a staticy TV with 'blobs' that
needed skill to interpret what they represented? Or something else
completely, like an oscilloscope type of display?

Thanks in advance. Tried googling, but didn't really know what to
search for.

Nick