Hi,

 

Just looking for some quick pointers on how to manage a desent in a stacked hold for the MD-11.

 

I have figured out how to enter the hold and exit using the FMC . Is the altitude controlled manually via the MCP or is there a way to manage this via the FMC?

 

thx

Mark

Is the altitude controlled manually via the MCP or is there a way to manage this via the FMC?

 

Don't be a slave to the automagic - descend on the MCP. I'm sure there's a way to get the FMC to do it, but it's simple enough to do on your own. It's not like you need to be in an economic descent mode for that 1000-2000'. In fact, I'm sure the controller is looking for ASAP, and not a lot of messing around with the automagic.

Use Vertical Speed. In the time it takes you to figure out how to do it nicely, you'll be half way to your new altitude.

 

Paul

Yep! I tried this out and it seems to work.

 

I entered the hold by having the altitude at the initial entry point into the Hold at the higher altitude, then program the Hold altitude in the FMC to the lower ALT. Once entering the Hold, you can descend using Vertical speed descending a 1000ft at a time for example and then finally exit the hold at the lower altitude. The only thing I notice is a CDU message indicating a discrepancy in the altitude which is expected but the procedure works perfectly well.

 

Thx for the tips.

 

Cheers

Mark

I would not advocate using the FMC in this situation, because when in holds, you are usually stepped down by ATC, and there is no way to pre-program the FMC to cope with that, also, there is no need to try since the alternate procedure is so simple. I would also recommend against using V/S as it could make speed control something of an issue, and that is not a situation you want ot get into in a crowded hold pattern. Easiest and smoothest way to manage a hold is to just dial in the next level you are cleared to and then pull the knob when you are ready to descend. The AP will back off the throttles, and pitch down to maintain speed, (which means you wont overshoot the turns etc.) and throttle back up as you get close to your target. All nice and smooth. And if ATC changes their mind in the middle, no problem, just dial in your new cleared alt and pull the knob again. When you are ready to exit the hold, just hit PROF to return altitude control to the FMC.

The FMS is for flight planned navigation. A holding pattern is not planned (it is planned for in fuel, yes, but you don't know that ATC will clear you to FL110 at 8:26 and 22 seconds local time, or when you will be vectored or tracked out of the hold before it actually happens). These are immediate clearances. When ATC clears you to decend to 9000ft, they want you to start decent to 9000ft within a few seconds.

 

There's no profile to follow in a hold. There's no decent angle that gets you to any point on your flightplan at a certain flight level when your holding pattern never passes that point, and you could reach the point after the holding pattern in 3 minutes if you left the hold now, but ATC won't let you leave the hold till the other 5 aircraft below you have already left. The FMC wants exacts. It wants to know that you will arrive at a waypoint in exactly 8 minutes and 22 seconds at 280 knots with wind blowing from 170 at 30 knots. It doesn't work when it thinks you will arrive at a waypoint in "When ATC tells you sometime within 1 hour from now otherwise we will have to divert and go somewhere else" minutes.

 

IN a holding stack ATC have aircraft stacked (hence the name) flying circles all in the same place, They want them 1000ft or 2000ft apart. If you get told to decend from 9000ft to 7000ft, they want you to be below 8000ft as fast as possible so the guy at 11,000ft can go down to 9000ft. If you take 5 minutes to start decending, you are making it harder for the ATC to accomodate aircraft above you.

Bingo.