Off Schedule Descent Light

[Guest MSMITH6]

Hey Guys-I will get an "Air Conditioning" warning light. When I look at the overhead panel I see the "Off Schedule Descent" light illuminated. My questions are:1. How do I turn the light off?2. Why does it come on in the first place? This happens when ATC brings me down lower before I have reached cruise altitude, so I presume that is the literal meaning of the warning.3. Why even have this warning as long as your settings for cruise and landing for pressurization purposes are within your operating parameters? I am running pressurization with the Auto setting.Thanks

[Qavion 19]

"1. How do I turn the light off?"Reset the Flight Altitude on the pressurization panel to below your current altitude"2. Why does it come on in the first place? This happens when ATC brings me down lower before I have reached cruise altitude, so I presume that is the literal meaning of the warning."Correct."3. Why even have this warning as long as your settings for cruise and landing for pressurization purposes are within your operating parameters? I am running pressurization with the Auto setting."Setting these values enables the controller to build a smooth pressurization ascent/descent profile.... for the comfort of the passengers and the integrity of the hull.Hope this helps.Cheers.Ian.

[Guest Lenny Zaman]

1) the light cannot be turned of normally, and alternate way is to reduce the cruise altitude to the current altitude2) no need to worry about the lightit indicates you're not reaching your cruise altitude set in the crz alt window.this is how it worksnormally, around takeoff the outflow valve closes and the aircraft is pressurised to a level of 200ft below the departure aerodrome altitude. then as you takeoff the outflow valve calmly opens and starts climbing to the cabin altitude(calculated automatically by the pressurisation compution) when you reach your cruise altitude the controller will keep the cabin altitude constant even if you make slight altitude changes, if you make a serious climb(i though 500ft or more) it will start climbing again to keep the differential pressure below limits. when you reach TOD and effectively start descending it will generate a smooth descent and make sure you're abour 300ft below arrival altitude when landing, this is done a bit early to make the approach more comfy. when touching down the aircraft automatically depressurises, no pilot input needed.If however you do not reach your cruize altitude the system will want to announce that the final cabin altitude is not reached. and the system will continue to keep the cabin altitude relative to the present aircraft altitude.note: when diverting to ALTN, reset the landing altitude to the ALTN altitude.

[Guest MSMITH6]

Thanks guys! A thorough explanation!

[Guest rcarlson123]

I've only done two flights with the 800, but in both of them, this light has come on, along with the "Air Cond" annunciation on the warning panel. However, in both flights, I reached cruise altitude and was at cruise for about an hour or so. (They were short flights.)What might I be doing wrong? Perhaps I didn't have the cruise altitude set in the FMC correctly?

[miguelpp 25]

Same here.Miquel Egea.

[Guest wkzzo]

set the cruise altitude on your pressurization panel to the same cruise altitude on your FMC.

[Guest rcarlson123]

Thanks! I have only done these two test flights and have yet to thoroughly read the manual. (I've only read the TCAS part so far.) I guess this wasn't modelled in the 600/700 since I never bothered with setting the pressurization altitude. One more thing for my checklist. :) (The more the better!)

[rdb 44]

I've encountered same problem when i left my crusing altitude using VS (not VNAV as usual) about 10 nm before TOD. The light won't go out even after landing and during whole next flight. The altitude controller and FMC were set properly for both flights.It finally go out when i restarted FS for third flight.Radek Bochenek