Unsafe Cabin Pressure

[RandallR 446]

Wayne,Set Cabin Altitude to 5000' w/climb at 500 fpm. After takeoff, close the dump valve and climb right on up to 30,000+'Anything "bad" happen?

[Guest Eagle]

OK Randall, I did as you instructed and had no problems. The pressure remained good and no warnings. BUT!!When I switched to Ventral Tank I received a fuel warning. That has not happened before. There is fuel in the tanks.

[Roger Mazengarb 0]

G'day Wayne,Mate I'm not sure you are interpeting the cabin pressure gauge correctly.It is a compound gauge giving three readings.Cabin altitudeCabin altitude rate of changeCabin/ambient differential>Good evening, Roger. Like you I just hit the red button and>turn off the warning. I trust this is a reference to the master caution lights. ie. the blinking lights on both the pilot and copilot glareshields. You gan't turn OFF the "cabin Altitude" warning. The only way to extiguish that is to get the cabin back below 10,000 ft.>Looking at the Cabin Pressure dial the needle with the red>x-hatch is about number 4. Yes this is correct. The red checkered pointer is the cabin/ambient differential pointer and this is indicating that the cabin pressure is 4.0 PSI higher than the outside (flight altitude) pressure. This means the cabin is way below the aicrafts altitude.The white needle is at 1 1/2. The>white needle will drop to 0 and the warning light comes on.>The red x-hatch needle stays put.This is correct. The white pointer you are describing is the cabin rate of change pointer. It was reading 1500 (1 1/2 x 1000) feet per min. but as you reached your selected cabin altitude of 10,000 ft it drops back to zero. (9 O'clock position. ie horizontal) Everthing is fine so far BUTthere is a third pointer (white) with a triangle at the tip which is reading cabiin altitude. It should now be reading 10,000 ft. You haven't made mention of this pointer??Because 10,000 ft is the altitude at which the "cabin Altitude" warning light comes on the light now illuminates. The master caution lights now start flashing away to bring to the pilots attention that the "cabin Altitude" warning light is ON.>Hope this makes sense. I can live with the problem, just>thought if it could be corrected that would be great.I'm not sure that there is a problem. Everthing you have described so far is correct. :-)Do it again Wayne and specifically check what the cabin altitude pointer is reading and get back to us. Cheers,Roger @YSSY

[Roger Mazengarb 0]

G'day Wayne,>OK Randall, I did as you instructed and had no problems. The>pressure remained good and no warnings. BUT!!Now you are cheating. :-)when you were getting the warning previously - that was correct ; you should have been getting a warning as you had selected and ATTAINED a cabin altitude of 10,000ft. ( dangerous stuff - you're flirting with hypoxia :-) )Now that you have reset cabin altitude to only 5,000 ft you won't get a warning. You have eliminated the cause of the warning.( ie. eliminated 10,000 ft cabin altitude)>When I switched to Ventral Tank I received a fuel warning.>That has not happened before. There is fuel in the tanks.Don't know about the fuel error. I haven't had any problems in the past. Will look into it.Cheers,Roger

[Guest Eagle]

OK Roger, here is what I did.Set Cabin Pressure Altitude to 5000 ft.Cabin Pressure Rate at 500 fpmDump Valve ClosedClimbed to 14,000 ft. and leveled off with no warnings. Opened Dump Valve as plane was climbing.White Point with triangle moved up as the plane was climbing until leveling off at 14,000 ft. The pointer then moved back down and held at 5.The red checkered pointer climbed to 3 1/2 and remained there.The white pointer remained at 500. After leveling off at 14,000 ft. The white pointer remained at 500 for some time and then dropped to "0". I am not sure if this was caused by my switching to Ventral Tank as I did receive a fuel warning at that time.Hope this helps. Let me know if there is anything else you would like for me to do.Don't want to go to 30,000 ft. as I am afraid of heights.:-zhelp

[RandallR 446]

That's right, Wayne - you now have no warnings as you have pressurized the cabin to a safe level. It wouldn't be uncommon to set the cabin altitude from 6,000 to 7,000 for those high altitude flights in the 30,000+ area, though I've found that the Hawker handles a setting of 5000 up to 32,000+ - I normally increase the cabin altitude setting to 6,000 when heading for the 34,000-35,000' level.Smaller aircraft can't handle that level of pressurization - the Malibu does pretty well (with Alex's fix :-) ) at 5,000 cabin when cruising at 20,000. I've found the Pilatus needs to be set to 6,000 cabin when passing 24,000 - the Socata requires 6,000 or higher for the cabin when passing 24,000 - 7,000 cabin does it at 26,000 in the Socata. The Kingair takes all the guess-work out of it by giving you recommended settings on the pressure setting dial (not that the others don't, the details are just too small to read). I hope this helps.As far as the Fuel Warning is concerned, it's just warning you that you have something special going on related to the fuel system - this warning will illuminate and you'll get caution lights when you use the Ventral Tank Transfer Switch. I don't know if these lights come on in the real Hawker when you do this, but it's no problem. From what I can tell, here's what's happening:1. When you select the Ventral Tank, you are not getting fuel directly from the tank - you are transferring (pumping) fuel from the Ventral into the Mains. The Hawker's engines only get fuel from the main tanks, so by transferring you are moving fuel from the Ventral to where it can be accessed.2. The caution lights will begin to flash and the fuel warning light will appear on the annunciator panel - turn off the warning lights...the annunciator warning will stay illuminated as long as you are transferring.3. Place your cursor over the small Ventral Tank indicator window in the center of the panel - you will get a little countdown window showing the percentage of fuel remaining in the tank. The percentage will count down before you. As the ventral pumps out look at the main fuel gauges - you'll see the levels rising as this new fuel is pumped in.4. If you allow all of the Ventral tank contents to be pumped, the cursor indicator will eventually reach 0% - at that moment a barber pole flag will momentarily appear in the Ventral indicator, then disappear. Turn off the transfer feed and the warning light will distinguish.You now have all the fuel from the Ventral added to the mains and all is well in the world. :-)

[RandallR 446]

Alex,Check my test results posted in the new thread:http://forums.avsim.net/dcboard.php?az=sho..._id=23779&page=

[RandallR 446]

Roger,I've posted my findings in a new thread:http://forums.avsim.net/dcboard.php?az=sho..._id=23779&page=

[Roger Mazengarb 0]

G'day Wayne,I think you may be confused with the dump valve position. If you left the valve OPEN as you say then your observations don't make sense.>Set Cabin Pressure Altitude to 5000 ft.>Cabin Pressure Rate at 500 fpm>Dump Valve ClosedNo problem with any of the above.>Climbed to 14,000 ft. and leveled off with no warnings.correct.> Opened Dump Valve as plane was climbing.Why?? you are flying a pressurised aircraft and decided to dump cabin pressure. The dump valve should be CLOSED. Just for testing I hope. >White Point with triangle moved up as the plane was climbingcorrect. You are now flying unpressurised. Initally the cabin altitude pointer would have been increasing at 500 ft/min but as soon as you OPENED the dump valve cabin should equalise with ambient and the cabin altimeter would increase at the same rate as the aircraft altitude.>until leveling off at 14,000 ft. The pointer then moved back>down and held at 5.No way should this happen UNLESS you closed the dumped valve and didn't tell me. :-) If you left the dump valve open the cabin would have arrived at 14000 ft at the same time as the aircraft AND you would have had "cabin altitude" warning and it would have stayed there as you are flying unpressurised.If on the other hand you have closed the dump valve and just forgot to mention it :-) then YES as soon as you closed the dump valve the cabin altitude would have proceeded to go from whatever it was when you closed the dump valve to 5000 ft at the selected rate of change. (500 ft/min.)>The red checkered pointer climbed to 3 1/2 and remained>there.Yes that's about right. The difference in air pressures at 5000 ft and 14,000 ft is about 3.5 psi.>>The white pointer remained at 500. After leveling off at>14,000 ft. The white pointer remained at 500 for some time and>then dropped to "0".Correct. The aircraft got to 14,000 ft quite quickly, the cabin took a little longer to get to 5000 ft. I am not sure if this was caused by my>switching to Ventral Tank as I did receive a fuel warning at>that time.Nothing to do with you switching anything Wayne. If the aircraft climbs at 3000 ft per min then it takes just under 5 min to get to 14,000 ft.If the cabin climbs at 500 ft per min it takes 10 minutes to get to 5000 ft.>Hope this helps. Let me know if there is anything else you>would like for me to do.Wayne I don't think there is a problem. I think (hope) you just got confused with the dump valve position. Try the below and see how it goes.For your own peace of mind repeat the scenario leaving the dump valve closedCheers,Roger @YSSY

[Guest Eagle]

You see how one word can get you in a whole bunch of trouble.The Dump Valve was open while on the ground and in taxi. After taking off the Dump Valve was closed, I believe it reads shut on the valve. Good to hear everything is working as it should. My thoughts at the beginning of this conversation was that the cabin pressure had to be set at 10,000 ft. if the plane was going above 10,000 and the rate should be set at 1,500 or higher. Between you, Roger and Randall, I believe I have got it. At least everything is working great.