Page 16 - Volume 15 Number 8

There are two or four switches to the left of the pilot’s control wheel: Two Engine Auto-Ignition switches and, for the later models, two Engine Anti-Ice switches. On the subpanel to the right of the control wheel we find a bunch more: Two Pitot Heat switches, two Fuel Vent Heat switches and a single Stall Warning Heat switch make up five of the switches on the right subpanel. These five switches have become known as the “Hot Five” and many King Air pilots operate them all the time when airborne, turning them on at “Runway Lineup” and off in the “After Landing” procedure. I have no complaint whatsoever with this process. However, I personally don’t do it. It’s not a POH procedure but rather comes from FlightSafety and U.S. Army training tradition. Wrong? No way! Maybe it’s because I have resided in Arizona for the last 34 years, but I just don’t see the need for running the Hot Five when it’s warm and clear, so typical of the United States’ southwestern states. My technique isn’t more “right” than running the Hot Five always, it’s just my habit/preference.
Another piece of historical trivia before I finish counting out the remainder of the ice protection switches: It’s impossible to turn on the Hot Five in a King Air 100 (the original “Straight” 100 made from 1969 to 1971, not the A100 nor the B100). The 100 model has no fuel vent heat! Although most of us think that the heated “standpipe” vent tube is a backup for the recessed vent (and that it is!) that’s not why it’s there. As you know, fuel vents serve two purposes. First, they allow air to enter the tank as fuel is consumed to prevent a vacuum from being created which could collapse a bladder tank. Second, they provide an overboard path for fuel when it expands, usually due to heat buildup, causing thermal expansion.
Apparently, both Beech and the Federal Aviation Administration (FAA) agreed that the recessed fuel vent on each side of a King Air, by its recessed nature, was not prone to becoming blocked by ice. Hence, no backup was necessary. In the model 100 only, enough expansion space exists in its tanks that thermal expansion causing the fuel to overflow the tank is not possible. The 100’s fuel system, although similar to the A90, B90 and C90 system has some significant changes. One of these is that its maximum capacity is 370 gallons, not the 384 of the others. No other King Air fuel system is exactly like it.
All the other King Air models, however, are capable
of thermal expansion causing the need to vent fuel overboard. If this fuel were to come out of the recessed fuel vent in flight, it would flow back along the bottom wing skin. A concern arises about the potential for fire caused by this fuel on the wing. Hence, the real reason for the standpipe vent is to expel the expanding fuel far enough away from the wing skin such that it blows away free and clear, posing no increased fire hazard. But, since this standpipe vent is indeed a ready collector of › ice, it has to be heated. That’s why all King Air models
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14 • KING AIR MAGAZINE
AUGUST 2021