Page 16 - Volume 11 Number 8

Ask the Expert
The Crossover Duct ... and
Why it was Eliminated
by Tom Clements
“Out of sight, out of mind.” That can be one that there will be no repairs needed in this section
description of the topic for this month’s article:
The crossover duct. Take a look at the image below, showing the forward portion of a model 90’s environmental system.
Do you see that dark blue and light blue tube that crosses from left to right, on the most forward portion of the diagram? It sits forward in the nose section, just aft of the bulkhead that has the radar antenna bolted onto it. It is totally inaccessible without removing lots and lots of equipment and panels. I have heard more than one King Air mechanic opine that Beech creates the air conditioning (AC) system first, then builds the airplane around it! Well, not really, but gaining access to the environmental components – air conditioner and heater – in the nose area is indeed a labor-intensive and time-consuming task. Keep your fingers crossed
Up & Over
during your next Phase inspection!
The fan that circulates air through the environmental components goes by the name of Vent Blower. Personally, I don’t like the “vent” portion of this label since I believe “venting” tends to involve air exiting some location or container. “Let’s open the kitchen window to vent out the smell of those rancid eggs.” Or, “I’ll open the valve on the bottle to vent some oxygen out to keep the pressure from being excessive.” Yet this particular fan merely picks up cabin air to recirculate it across the cooling and heating components before it flows through the outlets back into the cabin to repeat the process again. So I’d vote for just labeling it “blower,” but the Beechcraft engineers decided to label it “vent blower” so that’s the name we’ll use.
Down & Aft
RADOME
A Nose Circulation drawing of a King Air E90 which shows the location of the crossover duct – the dark and light blue tube – far forward in the nose.
14 • KING AIR MAGAZINE AUGUST 2017