Last month in my article regarding how to configure your King Air for in-flight icing encounters, I started reviewing the number of switches or push-pull controls that must be activated in icing conditions according to your POM/POH.
To review, 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.
As we continue counting the switches on the right side of the pilot’s control wheel, we come to the ones that use significantly more electric power than all of the Hot Five combined: Windshield Heat, Prop Heat and Lip Boot Heat (if applicable). In fact, for the C90-, E90-, F90- and 100-series, these switches constitute the “lock-out” items. Since the electric heater is only a comfort item – not a safety-of-flight item like ice protection – the designers never wanted the less-important components to rob power from the more-important components. Whenever any one of these lock-out item switches are on, all grids of electric heat become inoperative. Let’s discuss each of these anti-ice items individually.
First, Windshield Heat. Until the 200 model appeared, all previous King Airs had a single Windshield Heat switch with three positions: Up, labeled “Both,” to heat both pilot and copilot windshields; Center, the Off position; and Down, to heat only the pilot’s side. The down position is virtually never used. It would only be considered when one generator were inoperative causing total electric capacity to be half of what it normally would be. Be careful when moving the switch to Off from the Both position. Push down too hard and you will put it in Pilot Only. That increases the chance of blowing a current limiter during your next start.
For the 200-, F90-, C90A- and 300-series, there are separate switches for left and right windshields. Again, three positions exist: Up for Normal heat; Center for Off; and Down for High heat. Unlike the windshield on the other earlier King Airs, now nearly the entire windshield’s surface is heated, not just a horizontal strip across the lower third. Additionally, the heating elements embedded in the inner windshield layer run vertically, not horizontally as before. Surprisingly, when high heat is selected, the windshield’s thermostat control does not reset to a higher value. It still tries to keep the windshield’s middle ply at about 100°F. What changes is that about a 6-inch piece closest to the cockpit center post no longer receives any heat at all. By concentrating the available heat energy in a lesser size surface area there is an increased chance that the 100°F may be reached.
Whereas the switch on the earlier models was a simple three-position switch that required only one finger to operate, the switches on the later King Air models have the same appearance as the Auto-Ignition or Starter switches: a Lever-Lock design. The knob on the end of the switch allows it to be grasped so that it can be pulled out over the “lock” that prevents inadvertent activation. But wait! In truth, that is only correct when it is desired to move it down to the High Heat position. No pulling is required to go from Off to Normal or vice versa. I strongly encourage you NOT to use the grasping action you use on the starter switch. Instead, by using one finger only, you will avoid the mistake of leaving the switch in High when you meant to turn it Off. Again, you are asking for a blown current limiter when starting with the switches in High.
The Prop Heat switch, like Windshield Heat, may be one or two switches depending on the King Air model. When the 100-series appeared, they had both a Normal and a Standby Prop Heat switch. The weaker link in the Prop Heat system is the timer that directs the electric current to be applied to the different heating elements in sequence. The Normal and Standby systems use different timers. Similar to inverter usage, I suggest you use each system half of the time. There is no advantage of sticking with Normal over Standby.
In the 200- and 300-series, the Automatic Prop Heat switch – the one that uses the timer to direct where the current will flow – is accompanied by a Manual Prop Heat switch beside it. This switch is spring-loaded to the center, off-position and can be held up or down to activate the inner or the outer propeller blade heating elements. When the “Hot Prop” B.F. Goodrich design came out with only a single heating element per blade replacing the inner and outer elements, this manual switch became a two-position switch, spring-loaded to the down position and held up against spring tension to the manual position which heated both left and right props simultaneously. Remember that the current being used by the manual system – either the earlier inner/outer type or the later manual type – is more than can be displayed on the Prop Heat ammeter. Thus, the ammeter, in addition to the timer, is bypassed when the backup heat mode is used. Instead, a significant increase on the generator’s loadmeters verifies that current is flowing.
The original engine cowling on King Airs – generally called the “Chin-type Cowl” or just “Chin Cowl” – uses a rubber boot with an electric element inside to prevent ice formation on the cowling’s inlet lip by melting any ice that tries to form. Good airflow is necessary to transport that heat energy away to prevent the rubber from becoming so hot as to melt. If the heating boots were operated on the ground for any significant length of time, kiss the system goodbye. To eliminate this possibility, the Lip Boot heating circuit is wired through one of the landing gear “Squat switches” (also known as a WOW switch; Weight On Wheels). Not until the airplane lifts off does the circuit allow operation. It cannot be tested on the ground.
Every time the lower, forward cowling is removed for maintenance, the wiring to the Lip Boot must be disconnected. A quick-disconnect fitting is installed to make the job easier. Obviously, it is important that the disconnect be hooked back up correctly when the cowling is reinstalled. The mechanic, however, cannot verify operation on the ground. As the pilot, remember to turn on the Lip Boot heat switches when airborne on the first flight after maintenance. Then verify that each side, individually, causes a rise on the loadmeters – each boot pulls about 20 amps. The 100 and A100 models have a switch labeled Left and Right (although it operates Up and Down) that allows getting an actual readout of the current going to the respective lip boot. Instead of adding another dedicated ammeter gauge in the cockpit, however, they “Rob Peter to Pay Paul” and use the Prop Heat ammeter instead. The meter’s face is marked with separate green arcs for Prop and Lip Boot current, one on top of the meter’s white arc line and one on the bottom. Similarly, the F90 model has a voltmeter/ammeter selector position that allows lip boot current to be read on the overhead ammeter.
Probably more important than any other ice protection item are the engine Ice Vanes. I referred briefly to these when I stated that some models had four instead of two Ice Protection switches on the pilot’s left, not right, subpanel: Engine Anti-Ice. That is the “modern” name for ice vanes. No King Air is still in production that requires or allows manual Ice Vane operation. Yet from the mid-A90 production up through the B90, C90, C90-1 E90, F90, 100, and A100 the ice vanes were operated manually. T-handles are located beneath the pilot’s subpanel. When pulled, they extend the ice vane (there was only one movable part per side for many years, no bypass door existed) and an over-center action locked it in the extended, down position.
I used the following “laugh line” hundreds of times in the old days: “You can tell a new King Air pilot from the blood on his knuckles. You can tell a high-time King Air pilot by the fact his fingers are shorter than most.”
The “blood on the knuckles” comes from having difficulty in pushing hard enough to get the ice vane linkage to break back to the other side of center. In frustration, the pilot makes the big no-no of pushing harder on the T-handle while having his palm facing to the floor, not up to the overhead. Suddenly the mechanism releases, the handle slams forward, and a layer of skin from the pilot’s knuckles is now decorating the bottom metal edge of the subpanel. Ouch! Palm up is the only way to go!
(As for the shorter fingers? That follows all of the tapping we must do to get proper readings … on fuel gauges, loadmeters, prop ammeters, etc. Why are you nodding in agreement?!)
I have written entire articles in the past concerning the criticality of ice vane usage. Yes, many pilots have not yet been convinced of their importance and they are reluctant to extend them until ice starts forming on the wing. But I believe strongly that technique is misguided and is asking for an expensive repair to the ice-damaged PT6 compressor. I’m a lucky guy but I won’t tempt fate when it comes to engine ice vanes. “When in doubt, get ‘em out!”
Let’s review and count the various anti-ice protection items on your King Air:
- Auto-Ignition switches 2
- Engine Anti-Ice switches or Ice Vane handles 2
- Pitot Heat switch 2
- Fuel Vent Heat switch 2 (or none)
- Stall Warning Heat switch (if installed) 1
- Windshield Heat switch 1 or 2
- Prop Heat switch 1 (at a time)
- Lip Boot Heat switches (if installed) 2
This adds up to a total number of switches/handles ranging from 10 to 13, depending on the exact King Air model. In fact, some early long-range navigators included a heated probe as part of their air data system and a switch was placed on the pilot’s left subpanel labeled “Probe Heat.” Including that one, our count can reach 14.
“Wait a minute, Tom! You left out a couple that are on my King Air. I have left and right Fuel Control Heat switches, too.”
Of course, you are correct. Incorrectly, many pilots think these switches heat fuel. No, they’re not Fuel Heat switches but are Fuel Control Heat switches. They send current to heat the P3 air being supplied to the Honeywell (nee Bendix) Fuel Control Unit (FCU). Originally, the Beechcraft and Pratt & Whitney engineers believed that obstructing this line with ice would only be a possibility when flying in cold visible moisture. Hence, they located the switches on the pilot’s right subpanel right along with all of the other ice protection switches. However, it was found that, somewhat akin to carburetor ice, the blockage could occur even in clear air. When this occurred, the engine would lose all useful power as the fuel flow rolled back to Minimum Flow. Not good! The POM/POH procedure was amended to have these switches always on whenever the PT6s were running.
When the 200 made its appearance – and realizing that Fuel Control Heat should always be on when the engine was running – they were located inside the power quadrant activated by moving the Condition Lever from Fuel Cutoff to Low Idle. This became the norm for later models: F90-series and C90A and after series. (The Woodward FCUs on the 300-series, as well as on the PT6A-52 and -61 found on some 200s have no heating jackets on their P3 lines.)
A common question I am asked by pilots of earlier models that still have the switches is, “Why not just leave them on all the time?” The problem with this technique is that the heating element has been known to burn out when operated for too long without the flow of P3 air through the tube. This would be most likely during prolonged use of a ground power unit (GPU).
The majority of newer King Airs have 12 anti-ice items. Whenever I encounter “visible moisture with OAT at 5°C or below” then I count out the number of switches that I have activated. If I cannot find a dozen switches, I’ve missed something.
It is obvious that ice vane extension leads to a significant loss of engine power. When going into and out of icy clouds, my procedure is to immediately retract the ice vanes and turn off Prop Heat when in the clear (if it looks like we’ll stay in the clear for a few minutes) and re-extend them before penetrating the next cloud. Why kill only Prop Heat, not Windshield Heat also since they use similar amounts of current? My belief is that once the windshield has reached its proper internal operating temperature it is asking for trouble to allow it to cool and then reheat it again. A lot of windshields have cracked or shattered when heat is first applied. In fact, I always try to turn the windshield heat on before the OAT drops below freezing. Required? No. A good technique? I think so.
To conclude, be very conscientious and faithful about activating all of your ice protection items when in icing conditions. Failure to do so makes you noncompliant with the POH’s procedures. More importantly, however, it exposes you to needless risk.