Page 26 - July24

Since the pitot cowl of the 300 negates any oil cooling worry, the reason has nothing to do with the oil cooler’s effectiveness. Rather, it comes from wanting to ensure proper takeoff performance. When there is no need for ice protection, why subject the engine to the slight power loss that goes hand-in-hand with ice vane deployment? The “Minimum Takeoff Power” numbers – from the graph in the Performance section of the POH – are based on the assumption that ice vanes will not be deployed during takeoff when unneeded.
In a similar manner, this helps explain the 300-series’ POH statement that, on first reading, makes no sense: “For takeoff, Generator Load must not exceed 30% with air conditioning on, nor 50% with air conditioning off.” Since the condenser blower operates whenever AC is operating with the nose gear extended, and since this blower uses about 50 amps, it seems that the generator load would be higher, not lower, with AC on. Right? Yes, that is correct ... but it’s not what the restriction is addressing.
The engine is subject to three things that can cause available takeoff power to be less than optimal even though the engine itself is fine: (1) Cowling inefficiencies caused by ice vane deployment; (2) Compressor shaft load or drag caused by the need to drive the AC’s compressor (on the right engine); and (3) Compressor shaft load caused by generator load (on both engines). If we have
little electrical load – no electric heater or windshield heat in use – then we can abide by the AC drag and still have sufficient power available to the propeller to meet takeoff power design criteria. However, if the generators are working their guts out, then we don’t have enough “leftover” power to load up the compressor with the AC’s compressor drag.
To summarize then, the 300’s requirement to not use engine anti-ice for takeoff when OAT is above +10°C is based not on oil cooling concerns but instead is based on eliminating the cowling inefficiencies that could lead to the inability to meet the Minimum Takeoff Power target torque.
For all of the other King Air models – 90-series, 100-series – you, like the 300-series, have no tie-in between ice vane deployment and oil cooling. If you have a three-blade propeller, especially if it’s combined with the original “Chin” style of cowling, there is no concern about FOD due to ground debris even with the ice vanes retracted. On the other hand, four-blade props combined with the pitot cowl – F90-1s, C90As and after – have enough FOD potential that engine anti-ice ON while on the ground is strongly recommended.
But consider this: Leaving the ice vanes up on a four- blade 200 or any member of the 300-series is asking for FOD ... leading to a very expensive repair. But having the ice vanes down on your B90 causes no problems whatsoever. If you, like many pilots, fly a variety of King Air models, then there is absolutely nothing wrong with making “ice vanes down for all ground ops” your SOP (Standard Operating Practice). Are ITTs affected? Is engine starting affected? No! The only negative associated with this procedure is forgetting to retract them when taking the runway and hence being unable to attain your target minimum takeoff power.
I’ll leave you with this thought, readers: Forgetting to retract the ice vanes for takeoff may not be as bad as you think. Why? Because the ram air loss at takeoff speed – 100 knots? – is much less than what you are used to seeing when you pull those ice vane handles out (or activate the switches) before entering that cloud deck below you while in a descent going 200-plus knots. KA
King Air expert Tom Clements has been flying and instructing in King Airs for over 50 years and is the author of “The King Air Book” and “The King Air Book II.” He is a Gold Seal CFI and has over 23,000 total hours with more than 15,000 in King Airs. For information on ordering his books, contact Tom direct at twcaz@msn.com. Tom is actively mentoring the instructors at King Air Academy in Phoenix.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at editor@blonigen.net.
24 • KING AIR MAGAZINE
JULY 2024