Many thanks for this very detailed explanation, Mike. I can visualise
exactly what you are saying when reading the book.

(The episode I mentioned is on p 33 of the hardback edition, where Jake
is remembering a training flight in which Morgan is giving a running
commentary from his scope and then saves their lives by looking into
his scope* and screaming, "Pull up" after Jake had relaxed and
forgotten his scan. Sounds like Coonts may have used a bit of poetic
licence in giving the BN's scope elevation info.)

Thanks again,
Nick

* Coonts' terminology


Mike Kanze wrote:

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.


--
Nick
Mandrake 9.2
KDE 3.1.3