Page 4 - April24

CORRESPONDENCE
Correction to Pressurization article
Some of the text in Tom Clements’ “Pressurization Basics” article featured in the March 2024 issue of King Air magazine was mistakenly left out between pages 19-20. The text that was missing is below in red.
Our apologies to Mr. Clements and to the readers for any confusion this may have caused.
Inflow
The flow packs attempt to provide constant air mass flow regardless of altitude, outside air temperature or compressor speed (N1 or Ng). If compressor speed is too low, however, the flow cannot keep supplying the pounds of air that it should ... the air pump isn’t turning fast enough. A quick and unscientific check of your inflow and outflow is this: Can you maintain maximum ∆P with both power levers pulled back far enough to just trigger the landing gear warning horn? If the answer is no, then you can be sure that your air inflow is too low (weak or dead flow pack) or your air outflow is too high (excessive leaks) or a combination of both.
As you reduce power aggressively for a descent – either to comply with an ATC request or to keep the speed down due to turbulence – you may observe the cabin
starting to climb. In fact, I tend to watch the cabin’s vertical velocity indicator (VVI), more than torque or fuel flow, when I reduce power significantly. You may need to push the power levers back up a bit to keep supplying enough inflow to prevent the cabin from ascending. On the other hand, if you need to come down steeper, it’s time for landing gear extension and maybe, if it’s not overly turbulent, approach flaps too. Remember that the maximum allowable load factor limit is reduced when flaps are extended. KA
2 • KING AIR MAGAZINE
APRIL 2024