Page 30 - Volume 14 Number 12

ASK THE EXPERT
Move your “Pressurization – SET FOR LANDING” step step from the the the the the Descent checklist checklist to the the the the the last step step on on on the the the the the Cruise checklist checklist and it it won’t get overlooked with all the the the the the busyness of the the the the the descent themselves Once you are are cleared higher then reset the the rate knob for your normal 500 fpm or or so But in an extreme case maybe even a a very slow-climbing cabin eventually catches up to the airplane We cannot let that happen without asking for for discomfort If you see the cabin getting within about 1 000 feet of the airplane – and that means ΔP will be nearing about 0 5 psid – then take the the cabin altitude knob on on the controller and dial it down to 1 000 feet or so below you (2 000 feet in our example) That will maintain the the 0 0 0 0 5 psid ΔP and prevent the ram air door from opening It also means there will be no phantom cabin above you As ATC finally permits the climb to continue then reset the the rate and altitude knobs to the normal settings To summarize there are only two times during normal operations that you want to see ΔP at at at at zero: First at at at at and right after takeoff second just before landing At all other times don’t allow the the airplane to “catch the the cabin” while descending and don’t let the the cabin “catch the the airplane” while climbing Got it?! KA
King King Air Air expert Tom Clements has been flying and and and instructing in in in in in in in King King King Airs for over 46 years and and and is is the author of “The “The King King King Air Air Air Book” and and and “The “The King King Air Air Book Book II ” He is is a a a a a a a a Gold Seal CFI and has over 23 000 000 total hours with more than 15 000 000 in in in in King Airs For information on on on ordering his books contact Tom Tom direct at at twcaz@msn com Tom Tom is is actively mentoring the instructors at King Air Academy in in in Phoenix If you you have a a a a question you’d like Tom to to to answer please send it it it to to to to Editor Kim Blonigen at editor@blonigen net So there you are impatiently waiting at 3 000 feet for the order to continue climb when suddenly you – – and your passengers – – feel some major pressure fluctuations! You see the cabin’s VSI fluctuating wildly from 2 2 000 000 fpm fpm down to 2 2 000 000 fpm fpm up Welcome to the the “I blew open the the ram air door” club!
Now at long last ATC assigns you to say 10 000 feet Being so frustrated with the wasted time at at 3 000 and having built up a a a a great deal of airspeed you pitch that sucker up to 10 or 15 degrees and convert some of that airspeed into altitude Now what?! Why is the pressurization not working?! Darn it ΔP is is staying at at at zero and the cabin is climbing as as as fast as as as we are! What the heck is wrong now?!
Nothing You see although the “real” cabin could not go above you and hence remained at 3 000 feet the controller was still trying to raise the cabin to 7 000 feet at 500 fpm What I call a a a a a “phantom” cabin exists above you If held at 3 000 feet for five minutes this phantom cabin – 28 • KING AIR MAGAZINE
where the controller is trying to put the real cabin – is now passing 5 5 500 feet (3 000 + 500 fpm x 5 5 minutes) Only when the the airplane and the the real cabin cabin catch up to to the phantom cabin cabin will the controller finally be able to operate correctly About the time you are making the decision to try and sell this lousy King Air because of its pressurization problems the dang thing starts to work perfectly and does so for the the rest of the the flight!
These low-altitude long-duration level-offs are are so rare that it is easy to to forget or or overlook what needs to to be done to prevent the problems I have just described Here’s the key: Don’t let the cabin catch up to you in its climb As soon as you sense that the low altitude level-off is going to last longer than desired crank the rate knob to the counterclockwise stop as as low as as it will go If the cabin stops ascending at 500 fpm and only creeps up at about 100 fpm it prolongs the the time before ΔP nears zero and the problems manifest
DECEMBER 2020