Page 22 - Volume 15 Number 9

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
20 • KING AIR MAGAZINE
SEPTEMBER 2021