A-6 Redar Display?

Nick,

Got back my copy of FOTI this weekend and turned to the segment you mention.

From Coonts' narrative, the route sounds a bunch like the OB-16 route.
IIRC, OB-16 started in northern Oregon and ended at the B-16 nuclear
bullseye at NAS Fallon, NV. The early legs of this route took one into the
canyons of the John Day River system, including one particular canyon that
runs almost exactly N-S. After watching canyon walls go by for about 20 nm,
the terrain begins to broaden and you change course to roughly SSE for a ~70
nm leg to Harney Lake. The few charts I saved of this area confirm the
existence of some low hills and shallow valleys along this otherwise
flattening route. I would guess these are the hills Coonts was visualizing
as threats to Jake and Morg when he wrote this segment.

(For those among you who are limited to the likes of a Rand-McNally road
atlas, the route starts at a little burg named Kimberly which is about 60 nm
SSW of Umatilla, OR.)

There's no specific thing that Coonts mentions in his narrative that would
cause Morg to scream for a pull-up. Morg has just put his head back into
the hood, so he is not looking at the pilot's VDI. (Neither apparently is
Jake, since he is not maintaining the 1,000 feet of clearance he has cranked
into the VDI's offset impact bar.) Since Jake is viewing SRTC on the VDI,
Morg is limited to a PPI display on his DVI. Morg may have noted a
way-too-strong radar return too close-in for comfort. Or maybe things just
"didn't look right" to him, the sound of that little voice we all carry
within us. Or maybe this was just some artistic license taken by Coonts.

Night or IMC conditions are absolutely the most demanding environment for
low-level flight. Jake clearly has let his scan deteriorate away from the
SRTC info and (as the narrative states) dwell too much upon other things
like engine instruments and fuel state. Unless you're heading directly for
a canyon wall, your radar altimeter readings do not deteriorate from 1,000
feet to 100 feet in only an instant.

Coonts' narrative is one of many good examples of the value of having two
pairs of eyeballs sitting side by side for attack work. For low-level, all
wx ops this was the gold standard of that era. The
situational awareness such an arrangement facilitates - and demands - of
both pilot and B/N undoubtedly saved many a mission, bird and crew.

--
Mike Kanze

"It was like being a rat living under a bowling alley."

- Willem Dafoe, commenting on what it was like to sleep in a compartment
just below the flight deck of an aircraft carrier.



"Nick Coleman" wrote in message
...
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
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