Archived

This topic is now archived and is closed to further replies.

JSACKS

777: Cabin Alt emergency at FL410 - Incomplete procedure !

Recommended Posts

Still experimenting and learning this bird in MCP mode during early days:At FL400, all is well and on the EICAS I see cabin altitude is 8400 and the rate is zero. DP is 8.3 or 8.4, and Mach speed is 0.836. Pressurization on the overhead is in AUTO mode. All well and good.As the FMC tells me I can climb to OPT FL 429, I wind up the MCP ALT to 410 and hit FLCH. Initially, cabin alt FALLS all the way up but suddenly at 40,900', cabin alt reduction rate reverses and rises at +200-+300 fpm and then cabin alt busts 8500, I get red CABIN ALT on EICAS, siren blowing, DP rises above amber 8.5, N1 falls to 84-85%, FLCH levels me off below commanded alt, and speed bleeds off very gently down the Mach scale.I have experimented with putting pressurization into Manual mode and that works to re-balance cabin alt and DP to some extent in this situation, but I am unable to find an equilibrium level in manual mode and left fiddling up and down the scale all the time. And meantime, N1 remains in the 80s, falling gently, while Mach speed bleeds off further and I am stuck at 40,900'. Pitch rises to 3-4 deg and keeps rising slowly.I know pressurization was covered before in a thread, but I never saw anything conclusive about the procedure and about how to confirm and lock-in a recalibration of cabin alt, DP, and a solution for the N1 reduction and speed bleed.I don't think I've seen this covered in the manuals. Can anybody assist with this item?Thanks again!JS

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

I think I've solved this partially. It seems that this is related to weather and atmospheric pressure in some way too. I changed the weather from major thunderstorms below me to a fair westerly winds theme and lo and behold, cabin altitude fell dramatically in the process and I was then able to raise my MCP ALT and climb because I had enough of a margin of cabin alt and delta pressure. I "topped out" with cabin alt pressure of 8478 and DP of 8.3 at FL425 and was a happy camper. JS

Share this post


Link to post
Share on other sites