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Chu  Lai 
by Michael T. Martin



GCA radar screen

Not long after my possible extirpation in Marble Mountain, I was sent to help resolve a problem with the GCA at Chu Lai-a Marine fighter base on the coast south of Da Nang. Chu Lai was the first place Marines established a beachhead when sent to Vietnam. One peculiarity of that beachhead almost killed me stateside.

I enlisted in the Marines before the Vietnam War. I was first trained to work on medium range search radar used to acquire friendly aircraft for other radars to guide on bombing missions. Shortly after the Marines went into Chu Lai, I was living in a two-story barracks on a Marine air station in Southern California. As Christmas approached I was assigned to attach colorful lights to the roof of the barracks.

I went alone up to the barracks flat roof. I simply had to attach the string of lights to the edge of the roof. Except the lights in the box were completely tangled up. So I took them out of the box and began untangling them. As I walked backward on the roof stretching out the untangled lights, a distant sight startled me.

It was not unusual to see aircraft landing, but my attention was riveted to an aircraft plunging toward the runway. A C-130 transport plane, a large aircraft, descended nose first at about a 45 degree angle. The usual angle for landing is 3 degrees, so I fully expected a tragedy as this aircraft crashed in flames.

From 500 yards in the air the aircraft dove to within a few hundred feet of the ground. But at the last minute it suddenly flared into a flat landing on the runway. As I started breathing again, it dawned on me I was still walking backward untangling lights. I froze and looked behind me. There was nothing. I was standing on the edge of the barracks roof.

I found out later that this high angle landing was being taught to pilots for landings in Chu Lai. Normal low angle landings made them too vulnerable to being shot up, or shot down. Which is neither here nor there in regard to my now hitchhiking a flight to Chu Lai. I arrived safely and reported to the MATCU there. The officer in charge introduced me to their technicians and then showed me the problem.

It was a very unusual problem. The lines that were drawn as the glidepaths on the dual displays (elevation and azimuth) would suddenly shift across the screen unexpectedly. It didn't seem predictable or regular, it just happened frequently at unexpected times when an aircraft was being directed for landing. The radar operator would immediately abort the landing and have the pilot go around for another try. Meanwhile the lines on the display would just as suddenly return to their settings as if nothing had gone wrong.

I asked their technicians some questions about the problem. The officer in charge told me sternly not to stand around talking but open the radar and start troubleshooting. He then left us alone. I ignored him and continued talking to their technicians. The senior technician wanted to follow orders and started opening up the radar but I stopped him.

"This is a very peculiar problem," I said, "Why would a circuit suddenly shift voltages, moving the display, and then just as suddenly shift back?"

They didn't have an answer but I was reticent to begin troubleshooting because the lines had moved back to normal, so it was likely that all the circuits would have normal readings. That explained why their technicians had been unable to resolve the problem themselves.

"Something just doesn't seem right about this problem," I said to the technicians, "What would regularly turn on for a few minutes and then turn off?"

One of the technicians somewhat sheepishly told me that the air conditioning unit on a nearby repair hut was doing that, but it wasn't connected to the radar unit. His comment caught my attention, so I asked him some more questions.

It was hot in Vietnam. Electronic systems don't work well unless they are maintained at a constant cool temperature to keep them from overheating. The circuit boards with all the electronic parts were made of nonconductive resin or plastic. If they melted, electrical parts came into contact with conducting metals and short circuited, producing a puff of blue smoke.

A running joke told by technicians to the unsophisticated claimed that electronic circuits actually worked by pumping blue smoke through tiny pipes. The proof was that if the blue smoke escaped then the circuits did not work. We were 'blowing smoke' but it was true that running a radar system without air conditioning would produce a lot of blue smoke.

The technician who told me about the faulty air conditioning unit in the repair hut thought the air conditioner failure was an inconvenience but not crucial. It still kept the repair hut cool enough to work. However, I thought it might mean something else. I asked them for a voltage meter and plugged the meter leads into the wall socket of the radar hut. The wall socket was just a normal 110 volt wall socket like in an average home. The voltage meter showed that it had exactly that voltage. I told the technicians to wait a few minutes.

Soon, the background fan noise of the radar system changed tone. It did that whenever the glidepath lines were shifting on the radar displays. I pointed to the voltage meter, it now displayed well below 110 volts. That meant the electrical power being supplied to the radar unit was no longer 110 volts, which was why the circuits shifted. The air conditioning unit that went on and off was shorting out the power supplied to the repair hut, and that power came from the same generator that supplied the radar unit.

When we disconnected the faulty air conditioning unit in the repair hut 50 yards away from the radar system, the glidepath lines stopped shifting. There was really nothing wrong with the radar system. I told the officer in charge that their technician (who told me about the faulty air conditioning unit) had solved the problem. He really had, even though he didn't know it.

 

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