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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. KA
King Air expert Tom Clements has been flying and instructing in King Airs for over 46 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.
SEPTEMBER 2021
KING AIR MAGAZINE • 23