Page 20 - October 2022

“Tip: Should you ever see a sudden split in the ITT gauges for no apparent reason, this could signal a flow pack failure. The cooler engine has the dead pack.”
However, the scenario with a rising cabin altitude during descent was a fairly common complaint among King Air owners. It prompted Beech to switch to electronic flow packs which are not susceptible to clogging. Unfortunately they are a great deal more expensive to repair or replace in the event of failure.
Testing Flow Pack Efficiency
To test the efficiency of your flow packs, operate them one at a time while observing the cabin rate of climb.
Start with both packs going. To test the left pack, turn the right pack off and watch the cabin climb rate; it should go up briefly while the left pack adjusts to the change in flow, then it should come back down.
A strong flow pack can pressurize the cabin by itself. If the cabin climb rate goes up to 500 feet/minute, then that left pack is getting weak. Turn the right pack back on, allow for adjustment of flow, then turn the left pack off to test the right pack. If the cabin climb rate were to go to 1,000 feet/minute or more on such a test, you may have a dead pack and/or you have an excessive cabin leak rate that is throwing off the true results of this flow pack test ... more on that later.
Tip: Should you ever see a sudden split in the ITT gauges for no apparent reason, this could signal a flow pack failure. The cooler engine has the dead pack.
Identifying the Cabin Leak Rate
In troubleshooting a pressurization problem, identifying the cabin leak rate is essential. A leak rate of 2,500 feet/minute is considered ideal. The factory shoots for this on newly built aircraft. On a test flight, you want to get the cabin to maximum differential as shown on your cabin differential/cabin altitude gauge, OR you want
to get the cabin differential gauge as high as it will go without triggering the cabin altitude warning. Turn off both packs at this point. Observe
Finding Cabin Leaks
9 The only way to find leaks in the
the cabin rate of climb – that is 17 pressurization cart). Without one
your cabin leak rate. you are pouring money down the If you cannot bring your King 30 drain. You could spend a week
Air to maximum differential then you already know you have a major pressurization problem, but which one? Flow pack(s)? Cabin leaks? Both?
Even if you can bring your King Air to max differential, you should still test your cabin leak rate. I find the electronic flow packs can camouflage a high leak rate. If this
is the case in your King Air, and 9
sealing antennas and drains and barely gain a negligible improvement in the leak rate. With a huffer, the leaks are identified very quickly; then you can choose which leaks are the most cost-effective to fix.
Example: A B200 with electronic flow packs had a leak rate of 5,800 feet/minute. One pack was bad and was exchanged with an overhauled unit. Next, using the huffer, I found
pressure vessel is with a huffer (a
you suddenly have a flow pack 17 leaks at a number of screw holes failure, the remaining pack would with no screws. They were hidden
not be able to sustain the cabin 30 pressurization against the leaking cabin. Your cabin altitude would suddenly go up and you would have
to take appropriate measures very quickly.
beneath farings and I never would have found them without a huffer. I sealed those, plus a few more leaks that weren’t too hard to reach. Lo and behold, the leak rate came down to 3,100 feet/minute. There were
18 • KING AIR MAGAZINE
OCTOBER 2022