Page 25 - Dec 2022

The King Air model 200 was the first of the King Airs to have both an automatic and manual mode of propeller de-ice. All previous King Air models offered only the automatic system. The purpose of this article is to describe the system differences and to provide some insight into their use.
blocks and associated slip rings (two in the hot prop system which will be explained later) that are mounted on the backside of the propeller spinner’s bulkhead. To conserve electric power, the inboard and outboard heating elements work separately, not simultaneously. Each heating element uses about 5 amps of current and they are connected in parallel not in series. That means that about 15 amps total is required to heat either the inboard or outboard elements on a three-blade propeller and 20 amps is required for a four-blade prop.
The system is activated by turning on a single Prop Heat switch located on the pilot’s right subpanel. This is a circuit breaker type of switch that will trip itself to the off or down position if excessive current is encountered. On the pilot’s left subpanel, originally, and then on
All King Air models have been approved for icing flight and were standardly equipped with multiple anti-ice and de-ice equipment. This included, for most models, engine auto-ignition, engine anti- ice (inertial separators), windshield heat, pitot heat, fuel vent heat, stall warning heat, engine lip boot heat (for the original cowling design) and propeller heat.
Regarding the propeller heat system, up until about 1981 this system had both an inboard and
outboard electric heating element embedded in a rubber boot that extended from the propeller hub out to about one-third of the propeller blade length. Beyond that boot, there is enough centripetal force and blade flex that ice is not an issue. But near the hub, there is less velocity through the relative wind and less flex since the blade has not yet tapered from its “baseball bat” shape into an airfoil.
The heating elements are fed electric power via three brush
DECEMBER 2022
KING AIR MAGAZINE • 23