View Full Version : Cabin V/S up or down

10th Mar 2003, 08:52
You are flying along at FL410. Cabin altitude is 8000'. Delta P is 8.1 PSI.

You notice a crack in the windshield and consult the QRH.

It says
Max FL is FL230
Use Manual press. control as required to set

Delta P = 5 PSI & Cabin alt = 8000' (AT FL230)
Delta P = 5 PSI & Cabin alt = 6000' (AT FL200)
Delta P = 5 PSI & Cabin alt = 3000' (AT FL150)

Any ideas how you would handle this ?

10th Mar 2003, 09:26
Depending on the aeroplane, common sense says that you go to FL230 and make the cabin as high as possible to reduce the load on the windscreen pane.

Cross Check
10th Mar 2003, 23:00
Ditto ... window heat off (if a factor), set for a 10K' cabin, over to STBY and descend to reduce diff P (73 classics) ... no dramas, no great urgency, just keep an eye on it. Is it worth increasing the rate of ascent of the cab to relieve the pressure quicker? For 5PSID (-3psi) probably not, would only save a minute or so unless you really wanted to alarm the pax. For 2PSID (-6psi) might consider tweaking it up a little - depends on the window in question.

Would prefer not to turn the cabin into a rubber jungle, but if one wanted to be cautious, either (or both) could pop a mask on if the crack appeared to be spreading ... that or take the time to clean it first ... eeeww ... :suspect::hmm::ugh::yuk:

Having said that I'd probably finish my coffee, put the paper away and take the paperwork off the glareshield ... as much as one wants to, I hate losing paperwork. :uhoh::ouch:

11th Mar 2003, 03:05
Note that they recommend to maintain at maximum FL230. This is the first info you have to hold.
The second one is to maintain max 5 PSI. As 18-wheeler said, it's to avoid high pressure on the windshield.
The three options you've found in your QRH are advisory information. Depending on your minimum safety altitude, you can choose either. Or even descent to below FL100 and depressurize your acft.