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B-29s in the latter days of World War II. The company that designed and manufactured that system was Garrett AiResearch. So even today, most of us say it is an AiResearch control system.
The system is mechanical, using springs and vacuum. Electricity plays a minor role. In the King Air, the system uses electric power primarily for dumping: Opening a normally-closed solenoid valve that permits vacuum to suck open the safety valve and thereby create an opening (hole) so large that cabin pressure quickly equalizes with ambient pressure. In fact, the reason that a total loss of electric power in flight always leads to a lack of pressurization is not because the control system fails. No, it is because the inflow of air ceases. (Electric power is needed to keep the flow packs open.)
Somewhat surprisingly, since it is rather complex, the AiResearch control system is quite reliable. The problem with an airplane that cannot maintain the cabin altitude selected is very rarely due to a bad controller. Instead, it almost always is caused by too little inflow or too much outflow or a combination.
Troubleshooting Pressurization Problems
You have discovered that your pressurization is not working as it should. For example, you cannot reach 6.4-6.6 psid ∆P, or you see the cabin starting to climb even though the power levers have been only slightly reduced. How can you find what’s wrong? How can you help your mechanic reduce his troubleshooting time? Here are some ideas that pilots can do in flight. Mechanics have their own and, sometimes, more accurate procedures to use.
First, you can make sure the controller is functioning properly in this manner: In level flight, set the controller’s cabin altitude for 3,000 or 4,000 feet below you. For example, fly at 10,500 feet with the cabin set for 7,000 feet. Now zoom up to 11,500
MARCH 2024
and then dive down to 9,500 without changing engine power. Does the cabin stay level as it should? Next, back in level flight, dial the cabin up to, say, 9,000 feet. Does it start climbing? Twist the rate knob to the minimum setting. Does the cabin rate of climb decrease to almost nothing? Now spin the rate knob to maximum. Does the cabin climb like a homesick angel? Next, dial
the cabin down to a lower altitude and check the rate control again as it descends. In almost all cases, you will find that the controller is working perfectly. As I wrote above, it is a surprisingly robust piece of gear. By doing this test with a small difference between airplane and cabin altitude, ∆P is very low and thus the effect of excessive leaks or weak inflow will also be low.
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Main wheel & brake/ Rodas e freios principais
Kit P/N 199-90
Together, we can support all your King Air braking needs, one landing at a time.
Juntos podemos apoiar todas as suas necessidades de freio King Air, um pouso de cada vez.
The following King Air 90 models are now certified under European approval EASA #10039114 and Brazilian approval ANAC #9210-04:
Os seguintes modelos King Air 90 são agora certificados sob aprovação europeia EASA No10039114 e aprovação brasileira ANAC No9210-04:
• 65-90 • B90 • C90-1 • C90B • C90GTi • 65-A90 • C90 • C90A • C90GT • C90GTx
1-800-BRAKING (1-800-272-5464) Visit our website to see our full list of King Air conversion kits and more
www.kaman.com/cleveland www.clevelandwheelsandbrakes.com
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