Page 16 - August 2015 Volume 9, Number 8

Figure 4: Notice what’s wrong in the above picture? Someone has erroneously swapped the knobs on the ends of the cables. The parking brake should be silver; the firewall shut-off should be red.
What if we encounter “real” smoke in the airplane while flying? Maybe our Roots Blower developed a leak that allowed oil to mix with the air. How do we terminate the cabin air inflow when we need to?
On the pilot’s left subpanel is another push-pull knob, labeled “Press Air – Firewall Shut-Off Pull,” just to the left of the control wheel. When the knob is pulled, a mechanical shut-off valve located on the left engine
compartment firewall stops the flow of air heading toward the Flow Control Valve and instead dumps the air back into the engine compartment through a hole in the firewall, where it can escape harmlessly overboard through a vent on the left side of the nacelle.
While conducting flight training in these “mature” King Airs, I have found – more often than I’d like – that this firewall shut-off valve cannot be closed by the push-pull control. The lack-of-use combined with some corrosion probably has provided too much resistance. If you operate one of these old birds, please make sure you and/or your maintenance providers exercise this control with some degree of regularity to ensure its freedom.
However, what if we encounter environmental smoke in flight, try the knob, and find it’s stuck? Is there a workaround? Of course. Locate the “Press Cont” CB on the copilot’s left subpanel and pull it. Doing so will de-energize the Flow Control Valve and stop cabin air inflow, dumping the air into the wing where it can leak overboard. This method is not as desirable as use of the push-pull control since it allows the air to pass through the firewall and enter the wing. In most cases, that will be no big deal since typically the smoke comes from a minor supercharger oil leak. On the other hand, were there an actual fire ... hmmm, I hope that doesn’t happen and also that your push-pull control is not stuck.
Most of our readers will never have the opportunity to fly one of these old King Airs equipped with a supercharger. But for those who are flying one now or who will be flying one at some time in the future, I hope you’ve found this history lesson worthwhile. KA
About the Author: King Air expert Tom Clements has been flying and instructing in King Airs for over 43 years, and is the author of “The King Air Book.” 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 book, go to www. flightreview.net. 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 kblonigen@ cox.net.
14 • KING AIR MAGAZINE
OCTOBER 2015