Colyn,
I’ve not commented on this before, but for the Lancair
IV-P using the TSIO-550/turbo to pressurize the cabin (and this may not apply
to other configurations), it is not possible to maintain cabin pressure when
the engine is not producing power, or is off. The cabin is connected to the engine
intake system by a 1 ½” duct/controller that can only be turned off by
dumping it to the ambient atmosphere. The result is that the cabin very quickly
goes to engine intake or ambient pressure when power is reduced sufficiently to
spool down the turbos. You can test this for yourself by pulling power to idle
when pressurized and timing how long it takes to “back-flow” the
cabin air through the intake system…there is not a one-way valve in this
system. In my experience, the time required to reach ambient outside pressure
is a few seconds; certainly less than a minute at the max pressure differential
of 5.5 PSI.
Again, other aircraft/setups may work differently, but for the
IV-P with a TSIO-550 built to plans, I can’t see any way for the cabin to
be pressurized after landing. Other comments?
Bob
Paul
pointed out the obvious: a door with even 1 psi behind it is
dangerous. (1 psi times 600 or so? I don't have the
measurements)
So
I do buy the argument that at low throttle settings, and under normal
circumstances, you aren't going to have much residual pressure in the
cabin. But there are lots of possible failure modes here: a)
pressure controller malfunction b) pressure controller set way below landing altitude
c) exhaust valve is not operating correctly - not enough cabin exchange
rate. These may argue for the pressure switch
The
suggestion I like the best is "check cabin pressure before opening the
door".