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Lseatflyr

MD-11 Step-descents/Pressurization/Metric Cruise Alts

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Guys,I have a question that I'm having a hard time thinking of how to describe, so I'll start with a story of what I do and what results:Cruise Step-descents.Often found in Eurocontrol. It doesn't appear to be programmable in advance, 330/350/340, so I'm left with executing it in the air. My question is, how do I do that? My first few attempts have been to simply dial the new altitude on the autopilot panel and use a low v/s to descend. However, this causes the aircraft to go into descent mode, and the pressurization starts it's slow descent towards the airport. If I dial in the new cruise altitude on the INIT page of the FMC, the cabin altitude plummets and cabin rate warnings start popping up.I'm sure I'm just going about it the wrong way. I've searched through the manuals, and the FMC section explains the procedure the way I'm executing it, from what I can tell.Hopefully someone can show me the error of my ways.The next question will be about how to program metric cruise levels into the FMC, after I learn how to step down. Needless to say my flight from Leipzig to Bishkek is being flown in all the wrong modes for the last stretch after having to step down from FL350 to 10100m(FL331). Thanks in advance for any guidance anyone can give me!Tony Fiore

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I had a similar problem with some poor cruise level planning. After failing to reach FL360 due to it being way too high for my weight, I came back down to FL300. After a minute or so I got the cabin altitude alert, so switched the system to manual and controlled the outflow valve to get the cabin altitude back to the normal setting. For the next few minutes, I kept on switching the system back to auto, but it kept wanting to reduce the cabin altitiude. After a few minutes though, the auto mode eventually stayed at the current altitude.Conclusion - it seems it might take a few minutes of not descending further for the pressurisation system to realise you're not actually continuing descent and so switch back to cruise mode.

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I had to give it a try to see... I was enroute over Ohio from KIND to KEWR at FL330 and decided to descend to FL310. I change the glare shield altimeter window to 31000 (don't pull or press the knob), then set 310 on INIT page and it started a smooth 800 fpm descent and cabin altitude didn't change, and thrust stayed on CRZ. Using V/S mode means the FMS can no longer anticipate the path ahead, I suggest you keep it in PROF mode for step descents and that should keep the customer's ears happy.

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Phil/DanThank you both for the quick replies and insight. I'll keep in mind the fact that the aircraft may revert to a cruise mode after a few minutes of staying level after a step descent. If I have no luck with anything else, I'll just wait and try again.I think perhaps the sequence of Glareshield then FMC then (altitude change mode) have *a lot* to do with the pressurization and telling the airplane exactly what you're about to do *before* you do it. PROF probably plays a big role too, keeping the FMC in charge.Thank you both very much for the tips and ideas!Side note:Dan - I notice your test flight was a big FedEx route. If you're interested, here's a fun FedEx MD-11 flight... repo down to WRI, then run KWRI-EDDP-ORAA-EDDP-KWRI and repo back to wherever you want. (Step climbs based on a pax-configured MD-11, probably much lighter - so leave the steps up to your own discretion, except KABAN is the entry/exit point of Iraqi airspace)EDDP-ORAAN0476F330 TORPU Z21 OMELO UL620 RILAS/N0470F350 UL620 RIVOS UL851 KUGOS UT33 CRM UT34 SRT UR21 KABAN/N0475F370 R784 RAMPI L417 ALVIS/N0490F240 L417 SOGUM L126 PUSTO ORAA-EDDPN0490F240 PUSTO L126 SOGUM L417 ALVIS/N0477F350 L417 RAMPI R784 KABAN/N0476F360 UR21 SRT UG8 EZS UW710 SIV UW72 CRM UW86 SIN UT33 KUGOS UL851 ADINA UL624 ESATU/N0472F380 UL624 HDO/N0495F240 UM748 ESLOR M748 RENDO Q230 BEBEX T235 MITNI-Tony

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