Descent management

[easymxp]

Good evening guys, i would like your opinion. On A319 I rarely fly managed descent, of course in empty and free airspace i can use but in most of european airspaces I never use. I generally use either des or open des until maximum the reduction to 250kts then I usually go for V/S and follow heightx3 + 1 to Decel down to Sspeed +/- 1kt for each 10kts of headwind. It works quite good then at20nm, or 2000ft above platform altitude i start decelerating and try to perform a continuos descent. Using Des mode down to platform altitude I think is a bit too conservative because I level off for a few miles, then in airspaces such as london is quite impossible using. How do you usually perform descent? Differently or almost in the same way as me. Some colleagues love following managed des all the way down some others no

[JeroenC]

I fly Boeing, but VNAV equates to managed mode. The trick is anticipation. If I strongly expect (from clearanes to other AC or experience or just hoping) a shortcut I'll create a hard (lower) altitude at a relevant waypoint. When you realise you're not getting it, VS mode straight away. And of course using your rules to back it up all the time. If, when in managed or not, you get an unexpected shortcut it's again your rules (and speedbrake;)) to calculate if you can accept or not.

[BARKINGMAD]

I'm an ex-Boeing driver, but does your flight manual have such a thing as Performance Inflight figures/tables? This is a good place to start before you go on to get your own maths answer.

Mr B provides the makers figures for various weights from various heights in this section of the FCOM, then it's to you to acquire from LTCs or TRIs what are the 'bus corrections for head/tailwind and keep that going til the electronic glide or VNAV approach starts driving the 'frame.

Never put all your faith in the FMGC, garbage in-garbage out, and that includes actual winds differing from forecast and not just honest errors pre-loaded or mod'd by the operating crew.

Ask all the grumpy old pharts with whom you fly how do THEY do it, then distil your own figures, with which you feel comfortable, in order to stay out of rushed approach situations and undesired level flight portions.

Good luck, this question crops up far too often and I wonder what our TRTOs are doing by not addressing a fundamental but challenging path control problem. :ugh:

[flyboyike]

Relax, BARKINGMAD, he flies Microsoft, if that.

[easymxp]

Why do u say that?

[Going_Manual]

Quite simple really, if you are above the profile then no hurry to get down, just use a VNAV des mode 1,000 fpm, only time V/S is required, for me anyway is if I have a small climb or des of say 3,000 ft or less. as a general rule I like to use LNAV AND VNAV together, and HDG SEL AND level change together, don't forget if your leveling off and want to reduce the rate of descent, dont go straight for V/S!! reduce the A/S on MCP and this will pitch the nose up and give you a reduced ROD as you approach your new ALT, it will also wash off your A/S and when a further descent is given just increase the A/S and you will get a good ROD again. everybody wins.


Caution must be known however, and that will come with experience, for example if you are following a STAR and you think you are on profile because you profile indicator says so, it does not mean ATC will cut your route short and then you are suddenly way above the profile!! as I say this comes with experience. the best thing is to get down as quickly as possible with your own situational awareness of what you think may happen.


if its radar vectors then you will be in HDG SEL, so use your MCP speed and LVL change, if its a star, VNAV will do all the work and planning for you. just anticipate what will happen at restrictive way points, but be disciplined!! if you think VNAV is not behaving don't go staring for a selective mode! VNAV like to leave things right to the last and just when you think its not going to reduce the A/S or is not going to make the Next ALT!! it will!!! trust me I'm a doctor, I know its scary and you think you will bust your limit on the STAR but VNAV knows what its doing and does things right on schedule not 5-10 miles before its suppose to happen.


so in summary, have situational awareness, think where you are in relation to the profile! check your track miles to touch down! remember the X3 RULE? but don't forget to add your elevation to that figure!!! don't be in a hurry to reduce your airspeed to 250 KTS as you approach 10,000ft!! it will kill your ROD as you reduce and then you are playing catch up! it will take an aircraft 30 secs to decelerate from say 300kts to 250kts so chill out!! but obviously make sure you maintain 250kts at 10,000ft!!


if you are past your TOD point then you are already playing catch up, get down quick to try and regain your profile, if you get a message on the FMS saying reset MCP ALT and ATC has not given you descent yet, immediately reduce your A/S to the minimum available to you for the current weight, then when your cleared for descent, set a nice speed of say 310 kts if your have the balls, use your speed brake and your gonna get 5-6k fpm, once you regain the profile don't touch the A/S but put away your SB, you don't need it now until later, if possible try and get about 1500 below the profile and the start reducing A/S to say 260 kts your ROD will wash right off but as the profile bar starts to come up when you reach 260kts you will start to get 1500 fpm again and be perfectly on the profile.


when you get down wind start reducing to a lower A/S and start to take flaps, the you are good to go for the rest.