Page 26 - Volume 14 Number 12

ASK THE EXPERT
Catching the Cabin and Vice Versa
A re re you familiar with the the the the the title’s term “Catching the Cabin?” It usually refers to the action in in a a a a descent of having the airplane’s altitude altitude match the cabin’s altitude altitude Why does this happen? Three reasons come to mind First the the pilot forgets to set the the cabin altitude properly for the landing condition Especially when flying as the sole pilot with no one cross-
24 • KING AIR MAGAZINE
checking your actions it is relatively easy to miss the the step on the the descent checklist of setting the pressurization for landing Instead the pressurization controller (remember it is merely a governor of cabin altitude) remains at at the setting used for cruise say at at maybe 7 000 feet If the controller is overlooked then the the cabin remains at 7 000 feet As the airplane descends the difference between inside and by Tom Clements
outside pressure decreases of course That is is Differential Pressure (ΔP) becomes less Since it is impossible to have a a a a a a a a negative value of ΔP that means the cabin can never be higher than the the airplane So when the the airplane reaches the 7 000 feet in this example ΔP becomes zero the the outflow and safety valves are pushed open outside air flows into the cabin and the cabin descends right along
DECEMBER 2020