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The LNRS was present in SEA by early 1971 on 5 HH53Cs of the 40th ARRSq, then at Udorn RTAFB in Thailand. I received training in this equipment at Eglin in early 1971. It was truly a limited system, as will be explained below, but it did provide a useful night operation capability. The one successful mission that I flew out of NKP, though it was in the benign environment of Thailand, proved the value of the system. More on that later, after a description of the system.
The system consisted of:
1) a low light level camera (LLLTV) mounted externally on the left front of the helicopter, controlled by the pilot or copilot
2) monitors in the instrument panel directly in front of the pilot and copilot
3) a doppler navigation radar with fore/aft and side to side mileage readouts
4) a radar altimeter
5) a program for automatic letdown and hover, working thru the AFCS (automatic flight control system)
6) night vision goggles (army issue) were available to the flight crew
The operation envisioned was
1) to pass over the survivor, zeroing out the mileage readout
2) fly a square pattern,
3) on final inbound to the survivor, engage the automatic letdown program
4) the program would fly the HH53 at about 70 kt IAS, 500 fpm descent, to a 200 foot hover over the survivor's position (0/0 on the mileage readout)
Equipment limitations. Note that this was a USAF in-house (WPAFB) program with notable financial and development time constraints
1) The camera had no side-to-side scan, only fore-aft. With any wind the helicopter had to be oriented either directly into the wind, or downwind, to avoid the bank angle required for a crosswind hover even in the characteristically light winds of SEA
2) There was no way to control the camera aperture. Excessive light would cause the monitor screen to "bloom", blurring or wiping out the image..
3) Was the radar altimeter reading 200 feet to the ground or to the top of foliage? There were many trees in the SEA jungles that rose to more than 200 feet from the ground.
4) The night vision goggles were not helpful to the pilot while using the LLLTV, though they were essential to the FE and PJs. They focussed either at about two feet or at infinity. This meant that the instrument panel and monitors were always blurred. These "first generation" goggles were not good enough to really define the tree-top foliage. More on this later.
5) The automatic approach was not all that reliable, so approach to a hover, so far as I was concerned, was manual.
The successful mission I mentioned took place on 4 Oct 1971, to a US Army Signal Site on Phu Mu, a mountain 85 miles south of NKP. It was a medevac for a soldier that had gone off the side of a hill in his jeep; he was in very bad shape. Since we always had at least one night bird on alert at NKP, we scrambled immediately. As I came into a hover over the site, the mass of bright lights nearly blanked out the monitor's view of the area where the folks on the ground had gathered. We deployed the PJ via the penetrator, then lowered the litter. They could be seen on the monitor as they went to the ground. It was possible to hold the hover with no other reference than what could be seen in the monitor. The soldier was on board in 20 minutes and we took him to Ubon. The only thing that would have made the hover easier would have been less light on the ground but a call for less might have led to turning ALL the lights off - not a good situation.
The second opportunity for me to use the LNRS was much more serious. Two FACs were on the ground in Laos near the Catcher's Mitt and it was very late in the day - the sun had already set. Sandy led me in as his compatriots beat up gun positions not too far distant. It got real dark as we let down so the LLLTV camera was brought on line as we closed with the trees. With the camera pointed ahead I could get only a rough idea of the treeline; pointed down it gave no definition of nearby tree tops. The monitor was reacting unfavorably to the light from all the tracers as well. The question comes to mind - what about the night vision goggles? - and at this late date I can't say for sure. We did not have them on as we went in, probably depending on the LLTV to do the job.
The ground fire was not coming all that close, but with the visibility constraints concerning the treetops I decided that a hover for pickup was not practical. Rotating the helicopter about to find a horizon unmarred by tracers, I found a dark area and went for it. Fortunately there were no trees or hills in the way.
The story has a happy ending - next morning Ken Ernst made an unopposed pickup. The sequel at NKP is another story.
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