Dick, there is probably no better description of intake icing than that given by the famed aviation author Ernest Gann in "Fate Is The Hunter". He describes his experience as a youthful copilot in a DC-2 flying over a mountain range.
We have merely nodded to fear. Now we must shake its filthy hand.
Both engines are cutting out --- first one and then the other. For one awful moment they both subside together. And there is a silence which is not really a silence but a chilling diminuendo of all sound.
This is the way you die.
At three minutes past two in the morning.
And as, suddenly the engines regain themselves. We can feel the surge forward, but we have lost five hundred precious feet! We are below that peak, wherever it may be.
Something must be done about the engines. Nothing else is of any importance whatsoever.
Hughen has yanked on fun rich mixture to the carburetors. He switches back to the main fuel tank and works the wobble pump. All the while he struggles to keep the ship in a semblance of straight and level flight.
Again the engines grow feeble. They are stricken with a mysterious disease. We might, argue with our flying senses, but we cannot argue with a manifold pressure gauge. Both instruments show a slow and steady loss of power. This cannot be due to carburetor ice. We are certain of that because other instruments tell us the heaters are working.
We lose another two hundred feet. Hughen anxiously jockeys the throttles. He checks the magnetos. Perfect. He steems more perplexed than frightened and I cannot think of a way to help him.
We are much too low. We can only be flying in a valley, but it is impossible to determine which valley since there are several shown on the chart. Nor can we know when this convenient valley will come to an abrupt end. Hughen begins a slow circle. Flying so, we will at least use up less territory.
"Maybe I'd better go back and start heaving things overboard." We must, absolutely. must, have altitude.
"Wait. I may need you."
Hughen has switched on the landing lights again and yanked open his side window so he can see the left engine clearly. After a moment he hauls the window shut. Then to my horror he cuts off the fuel mixture to his engine. Starved of fuel, it backfires angrily. At once Hughen pulls the fuel lever to full rich again. The response is like a cheer. His engine is putting out full power once more. He repeats the action with the right engine controls. Again, after a moments startled regurgitation, a welcome return of power.
We are able to climb at fifty feet a minute!
"Air scoops . . . icing over. Watch them. Soon as the power falls off, cut the mixture until they backfire. Then. slam them on again."
I must lean forward to see past the accumulation of ice along the fringes of my side window. It is swelling rapidly and is easily three inches thick in places. Beyond it, in the ghostly light, I can see the engine, now grizzle-bearded in ice.
The carburetor air scoop is an oval-shaped metal mouth on top of the engine. Through it must pass the air, which is as important to any combustion engine as fuel. Without air the engine dies as surely as a drowning human being. Normally, the mouth is approximately four inches wide. Now the reason for our loss of. power becomes all too obvious. Even as I watch, the ice accumulates around the lips of the mouth. It builds upon itself, decreasing the size of the opening like a closing iris until it is merely a black hole hardly more than the size of a dollar. The same thing is happening on Hughen’s side. Our engines are simply suffocating. Something must remove the ice before it closes their mouths entirely.
Hughen has had the nerve and courage to find a way. By backfiring the engines a tongue of flame spurts from the air scoops. It is not the flame but the force of air from the bowels of the engine which knocks away the closing ice. Two hefty belches seem to do the job nicely. Then there is a wait of three or four minutes until the danger point is reached again. It is a terrible abuse of the engines, but not so bad as asking them to fly through a mountain. Gradually, Hughen is able to nurse the ship to 4,300 feet. But even at full power, that is all. He holds the course reasonably steady on southwest, the direction from which we have come.
Between backfirings I am heavily engaged with the loop antenna. With luck, our position will again become important.
I am able to plot a series of bearing fixes. They show without doubt that retreat might be our salvation.