Kingair question

[boofhead]

What is the best way to operate the E90 pressurization system for a flight at 15,000 feet? Do I need to set the altitude at that figure or can I set it higher, or lower? Do I need to move the rate selector at all? On descent can I leave the altitude at 15,000 and accept the loss of cabin pressure as the airplane descends, or should I set some altitude above the field or below the field altitude? I am looking for a simple way to teach it and to avoid unnecessary differential pressures. For example if I set 20,000 and leave it, the cabin alt goes up to less than max, and comes down again nicely with no negative pressure or pressure spikes, is there some aspect I am missing? .(such as pressure locks on doors, high cabin rates of descent etc). Another way would be to set, say, 1000 feet cruise alt, let the diff go to max and hold there. Does the airframe have any problem with fatigue caused by using high diff pressures?
I have seen several ways that people have operated the system, and there is nothing in the flight manual to cover this subject.

[mildly amused]

KA cabin

Just set it to 1000 feet above cruise level prior to take off

then set landing alt plus 500 feet at the tod

turn the knob slowly when setting the descent with ref to the cabin vsi

thats how we do !

[boofhead]

Thanks, that's simple enough.

[crochunter]

If you want to make things way simpler and impossible to forget to set the pressurization to airport elevation prior to descent, here's what I do-

Granted, it's not the ''proper'' way however the B100's I fly can't max the differential since they leak (age I guess) Check yours to see if you stay in the green before making a habit of it so you're not bouncing off the safety valve all time.

During climbout, after takeoff checks, in cruise, before descent....whenever doesn't really matter, Set destination airport (taking into account barometric pressure) + around 500' in the control panel. Don't bother setting 1000' above cruise if your plane won't maintain max diff.

For the climb, I set the rate knob fully closed (turn knob left) Before the descent I'll open it slowly to give me the rate of descent I need not exceeding 500FPM.

There you go.

easy, safe and simple.

[boofhead]

Does the pressure fluctuate when controlled by the safety valve?
I had thought of just setting the altitude 500 feet above the landing altitude for the entire flight and letting the outflow valve maintain the cabin pressure appropriate to the max diff. I see around 4.5 in normal operations so it must be a good cabin with no leaks. For flights around 15,000 that offers an easy way to do it, but are there any problems I have not considered?
Another consideration is the wear and tear on the airplane and it might be better to fly for minimum differential. Setting an altitude of, say, 24,000 feet would give, at maximum diff, a cabin altitude of 10,000 feet.
But I am not able to determine the pressurization schedule. Does the system go to maximum diff (or to the highest value needed for the cruise altitude selected) or is it proportional to the cruise altitude and actual altitude being flown? For example, if I set the cruise altitude to sea level and flew at around 1000 feet, would the cabin go to an altitude below sea level?
Is it always trying to go to max diff or is it more intelligent than that?

[crochunter]

it'll always go towards max diff if the controller is set at cruise alt or below (landing airport elevation)

To limit the differential, you can control it by turning the controller above the cruise alt.

I don't think there is anything wrong with running at max diff airframe wise. It's designed for it and makes planning you descent easier with a lower cabin descent rate as well (fpm)

[boofhead]

You are right. And if I try to fly with a higher cruise alt selected, all the flight below the associated cabin alt will be unpressurised, meaning I would still have to select a landing altitude before descent and when I do that the diff will increase anyway, so nothing will be gained.
Thanks for the information it is appreciated.

[boofhead]

had a chance to fly a couple of longer flights today, used the technique of setting the alt 1000 above cruise, and setting 500 feet above landing altitude on descent. It worked well, except that for flights above 24,000 feet, when setting, say, 25,000 on the press control, we got a cabin alt over 10,000 with an associated altitude warning light. Cabin holds 4.6 diff with no problem.

Another thing I have noticed is that we rarely get an auto feather arming on takeoff due to the low N1 (below 90 percent), even using 1300 tqe. In the summer the rpm easily exceeds 90, but in the winter it reaches only 88 percent, which means the auto feather will not be available in the event of an engine failure.

Interesting airplane. Nice to fly though. Got a sim check next month, hope I have learned enough by then..

[powerstall]

we also use the same technique when flying with 350's and B200's, 1,000 ft above the cruising altitude and 500 ft above the airport when descending.

normally when cruising at FL250 you wouldn't get the associated alt warning, have you logged the event? have it checked by your ground mechanic.

just my two-cents!

[boofhead]

At 240 I was able to send the cabin back below 10,000 and it put the light out, but at 250 we were already at the max diff and I could not get the cabin to go below 10,000 enough to re-set the warning. I will ask the pilots to set the cabin just below 10,000 in future. Luckily we don't have an aural warning of cabin altitude.