Our mission this morning was to photograph some enemy activity areas northwest of Saigon. But now we were cruising at 27,000 feet in the crisp cool air. Outside air temperature was -20 degrees, though at ground level down below it was approaching 90.
"There's the fork in the river, Bill," I exclaimed. "Over there at 2:00 o'clock. That's the lineup point for our first pass. Time to begin the letdown. Photo altitude is 1000 feet above ground level (AGL)."
"Got it," Bill responded. "Checklist."
I began to read the pertinent checklist items for our rapid descent into the target area. Bill responded as each action was completed. Everything was going smoothly as we came on down in a spiraling turn.
"We want to cross over that fork in the river on a heading of 345 degrees," I reminded. I'll start the clock as we cross the shoreline."
15,000 feet, 10,000 feet and our descent was right on line. But as we passed through 3000 feet, suddenly everything disappeared. The inside of the Plexiglas canopy quickly clouded up with a fog that totally obscured the outside world.
"Damn, " Bill muttered. "Full cabin heat and windshield de-fog."
It took almost a minute to clear the canopy of that interior fog obscuring our view. We hadn't thought about the atmospheric conditions that combined to create our instant canopy fog. We had been comfortably cruising for an hour in that cold air aloft. Our aircraft was thoroughly cold-soaked, including the thick Plexiglas canopy. But as we brought that plane rapidly down into the warm moisture-laden air on the deck, we experienced instant condensation. The warm cabin air immediately deposited its moisture on the inside surface of the cold plastic.
"Level off at 1500 feet, Bill, " I cautioned. "Take up heading 345 now. I've got the river fork on the radar. We're okay."
Just about the time we passed the river fork and continued down to 1000 feet AGL, the canopy cleared, but there was another problem. There we were down in the 90 degree moist air with cabin heat turned up full. My god were we sweating. Perspiration poured down my forehead, like a shower coming from under my helmet. Only the cool air/oxygen mixture through the facemasks provided any relief.
"Enough already. Turn down the heat, Bill. I'm drowning in sweat. Cameras on in 10 seconds."
"Yeah, yeah .. I know. But I don't want us to fog up again down here in the weeds. I'll turn it down gradually and let's see what happens."
Mercifully, the drop in hot airflow through the cabin didn't cause the canopy to fog up again. We could now bring in some cooler air and feel comfortable again.
That's just one minor complication of flying low level photo recon in the tropics. There were others, including an enemy taking pot shots as we flew by.