Unsafe Cabin Pressure

[Guest Eagle]

I have recently flown the Hawker and whenever I get above 7,000 ft. I ge the alarm of "unsafe cabin pressure".The Dump Valve is closed. After departure I turn on the right and left Main Air Valve.I don't have this problem in the other aircraft. So what am I doing wrong?

[Roger Mazengarb 0]

G'day Wayne,You also must set a selected cabin altitude and cabin rate of change on the auto controller. From memory also the right and left main bleed air valve operations are reversed. So leave the valves closed and I think you will find the pressurisation sytem will then work perfectly.Cheers,Roger @YSSY

[Guest Eagle]

Thanks, Roger, for the suggestion. It didn't work as I keep getting the warning. May be something with the installation of the file for the plane, but I am not about to reinstall Fly!!

[Roger Mazengarb 0]

G'day Wayne,Don't even contemplate reinstalling Fly! II. !!!!I have just been testing but unfortunately I cannot reproduce your problem. On my computer the bleed air switches have absolutely no effect. Both bleed air valves are permanently frozen in the open position.Try deleting the history file *.hst (C-goss.hst)for the hawker. It's not uncommon for that to get corrupted and cause all sorts of problems. Since other aircraft air working fine then that would be my best guess. "unsafe cabin pressure" (grey with white text) is a generic Fly! II caution NOT a specific aircraft warning."Cabin altitude" {in the annuciator panel on the Hawker} comes on at 10,000 ft cabin altitude.If just deleting the Hawker *.hst file doesn't solve your problem then try deleting all hst files in your aircraft folder(just in case it's an hst from another aircraft that is causing the problem.Just another thought: What is your startup aircraft? Try making either the Cessna or Kodiac your startup aircraft and see if that helps.Don't reinstall Fly! II. Get back to the forum if none of this helps.Cheers,Roger @YSSY

[RandallR 449]

Wayne & Roger,I have had no problem with pressurization in the Hawker (sure wish that was the case with the Malibu, but I believe it was broken in the conversion to Fly!2 and was on the "fix list" at the time of Rich's death).Here's the procedure I use:1. Dump Valve open2. Set Climb Rate and target Pressure Altitude3. Shortly after takeoff...both Main Air Valves to Open - that's two mouse clicks on each. One click will only take you halfway to LP On - take them all the way to Open (I double-click 'em).4. Close the Dump ValveI've had no problems with this procedure - you may be doing the same thing - just checking.

[Roger Mazengarb 0]

G'day Randall,Procedurally your list is perfect.Please check this for me. Eliminate step 3 from your list and see if it still works. I don't have to open the main air valves and the aircraft still pressurises normally. - just curious, I always thought that this was just a bug with fly! II but now you got me wondering if it's just my installation. :-) Cheers,Roger @YSSY

[Guest Fly II Pilot]

Randall,I just took a quick look at the Malibu's AMP and PNL files. I made some changes and I think now the Pressurization system is working properly. Could you give it a try?The problem in the AMP file was that there was no differential pressure set. The problem in the overhead PNL file was that the switch was reversed. The normal position should be CABIN PRESSURE and the abnormal should be DUMP.Regards,http://www.avsim.com/hangar/fly/dfdg/banneraa.jpg

[RandallR 449]

Alejandro,If you've fixed this old wart, you deserve a medal! I received the files - I'll give 'em a try tomorrow night, as it's now past my bed time.

[RandallR 449]

Hi Roger,Be happy to try it - be back with a report in about 24 hours.

[Guest Eagle]

Randall, I did everything according to your steps above and all is OK. No more warnings!! I used only one click for the Main Air Valves instead of two, but you are correct that the Dump Valve should be open as that is the condition it should be in when landing.Thanks

[Guest cord]

Can you upload the fixes you made for the Malibu and maybe to the Hawker ?Thanks in advance.Cord

[Roger Mazengarb 0]

G'day Randall,Nope! My procedure is totally different. Maybe not technically correct for this aircraft but it works 100% for me. I have just finished an exhaustive test of the Hawker pressurisation system.At the terminal gate :-)1. shut the dump valve2. set selected cabin altitude and rate of change.Start engines.3. Main air valves (can be left off or on - makes no difference)taxi out and take off.climb out at 3000 ft per min.Too busy on the radio and setting up the autopilot to have time to be fiddling about with the pressurisation controller. I don't have a copilot- :-)Anyway using the above procedure I checked out1. selected rate of change mode.- works with both ascending and descending selected cabin altitudes.2. isobaric mode. - maintains selected cabin altitude irrespective of aircraft altitude within the confines of differential limits. 3. differential mode. - maintaining a constant cabin/ambient differential once max diff is reached.4. negative relief. This appear to be a little dodgy as it appears that pressures only equalise at selected rate of change instead of flooding in."Cabin Altitude" warning comes on at 10000 ft cabin altitude and I must admit to being quite impressed with what TRI have done with the pressurisation system, especially since 90 % is transparent to the user.As for the dump valve - some aircraft use an air/ground safety relay operated by a switch on the MLG scissor links to operate the saftey valve AS WELL AS a panel switch. Such MAY be the case of the Hawker as if you leave the dump valve closed and then land with a slight differential you can see the cabin pressurisation gauge needles all snap to zero as you touch down.A big "Thumbs up" for the Hawker pressurisation system. :-)Cheers,Roger @YSSY

[Guest Fly II Pilot]

Randall,Did it work?Keep in mind that the file I sent you is the original Malibu's AMP and PNL files. If there have been any fixes to either of these files then I'll have to incorporate these changes to those newer files so I don't end up breaking something that had been fixed.Take care,Alexhttp://www.avsim.com/hangar/fly/dfdg/banneraa.jpg

[Roger Mazengarb 0]

G'day Alejandro, Tri have modelled the Malibu incorrectly. there should only be one dump valve control in the cockpit and that is the rocker switch on the O/H panel. There is also a switch on the MLG (in parallel with the cockpit switch) that also controls the dump valve. whenever the aircraft is on the ground the dump valve is commanded open irrespective of the cockpit switch position. The cockpit rocker is just for emergency depressurisation whilst airborne. The knob on the main panel is NOT a control for the dump valve. It is the emergency landing gear extension control. I'm hoping to get confirmation as to whether the main bleed air valves on the Hawker overhead function. As far as I can determine they do nothing and the bleed air valves are always open.attachments are pages from Course notes.Cheers,Roger @YSSY

[RandallR 449]

Alex,Yes, they worked!! Sorry about the delay - a change in my work schedule didn't allow me to fly until today. There are a few items that probably need adjustment, but I can verify that indeed the Malibu now pressurizes correctly!When I entered the aircraft, I noted that the Pressurization switch was ON and the Dump switch was set to the pressurize position. Isn't this backwards? Wouldn't a pilot leave the pressure system in the dumped and off positions when shutting down the aircraft? Regardless, I turned the pressure system off and set the Dump switch to dump before I started the aircraft.First test:- I wanted to see how it would handle a matched altitude pressurize, so I set the climb rate to 500 and the pressure altitude to 5000- I took off, noting that the pressure indicator represented the change rate properly and showed the cabin altitude increasing with the outside pressure.- at 5000 MSL I threw the Dump switch to pressurize and turned on the cabin pressure system. The internal pressure indicator remained at 5000 and the indicated pressure climb rate dropped to 0 - well done! I continued climbing through 12,000 with no warnings or decrease in cabin pressure.Second test:- This time I used a more standard approach. before takeoff, I set the climb rate to 500 and the pressure altitude to +500 of the field altitude.- I took off, noting proper change rate. The cabin altitude held at 2000, my initial setting.- After turning on course, I increased the setting to 5000. The indicator showed an increase rate of 500 and cabin pressure climbed to 5000 and held. Worked beautifully! I continued the climb to 15,000 to check out the indicator. The indicator showed an altitude of 4,000 for external pressure, so it's way off - everything else was on the money!So, here are the only issues as I see them:1. Pressure dial indicates improper outside pressure2. Cabin pressure set to ON at startup3. Dump set to pressurize at startupThanks so much for this!