Heavy use of speedbrakes and their effectiveness

[Lek767 37]

Ok, but with thrust at idle and speedbrakes fully extended is a 1000-1200 ft/min descent rate realistic?

 

Well, that's very much dependent on your airspeed,of course. The lack of that bit of information makes answering your question rather difficult...

[Spin737 102]

Ok, but with thrust at idle and speedbrakes fully extended is a 1000-1200 ft/min descent rate realistic?

That or more for a minimum.

[WebMaximus 372]

Mostly I find myself in a situation where I'm having trouble slowing down when descending below 10k where you're normally have a speed restriction of 250 knots and flying in VNAV mode the FMC wants me to be even at 240 or less and to keep below this speed my decent rate at idle thrust and with fully extended speed brakes is approx 1200 feet/min often resulting in coming in too high.

 

Guess I'll have to start planning more myself rather than trust the FMC and the VNAV mode.

[ctdesing 5]

Speed Brakes are not Required if you are flying within VNAV PATH as it is calculated with speed brakes down. But when ALT Restriction are so closed that the current drag is not enough to comply with the restriction the Speed Brakes will be needed.The descent rate with speed brakes up will depend on aircraft Gross Weight. The best way to descent when ATC doesn't give your descent clearance at T/D (i haven't seen this on fsx) is to select DES NOW on VNAV DES page if you are before T/D (it will descent at 1000ft/m to intercept VNAV PATH. If ATC request you to expedite your descent this is not an option) or Descent as fastest as you can go (no need to use speed brakes) if you are after T/D until intercepting VNAV PATH.

[NM5K 1]

I don't see that problem too much even VNAV.. Every once in a while, but not very often.

There should be a decel point before you start getting too close. It's usually at a point

where you have plenty of time to get it slowed down by the time you get to the airport.

And if following the normal flaps sked, the FMC should keep reducing the speed as you

go along.

Only when I get a FMC plan that is whacked for some reason, have I ever had a problem

with that. But I do descend semi manually most of the time. I'll run LNAV/VNAV until I get

close to the FMC planned TOD, and right before that, I switch to MCP speed and ALT.

And the rest is pretty much dialing in what I want manually, according to what ATC tells me.

 

The ATC TOD will usually be slightly different from what the FMC wants to do.

So from that point, VNAV is a goner.. I keep running LNAV until ATC starts steering me,

and then it's off too.

I usually start most of my descents at about 2200 fpm, and I gradually shallow up a

bit as I get closer to dirt. I'll usually be descending at about 1200-1400 fpm when passing

through 10k, and even shallower as I approach the ILS.

But.. I'm sure I'm not exactly following any specific airline, and I don't have anyone

telling me how to fly. So I get to make my own rules.. I'm so used to the ATC routes I

use, I know what fits the best. lol..

 

But I can set it up and fly LNAV/VNAV from 400 ft, all the way to an autoland, and usually

don't have any trouble.

Course, I'm usually playing Southwest buoy, and they don't do autolands. Pretty HGS

driven.. I can land in fog so dense you can't see the runway lights just using the HGS

and flying by hand.

[skyhawker22 1]

Make sure you are inputting descent winds into the FMC, so it can adjust TOD for headwind/tailwind, also what makes a great difference is whether you have to have eng anti-ice on during the descent. Input those values and see how it works out. You will still need to use speedbrakes for fine tuning, unforecasted conditions, etc...

[ctdesing 5]

Make sure you are inputting descent winds into the FMC, so it can adjust TOD for headwind/tailwind, also what makes a great difference is whether you have to have eng anti-ice on during the descent. Input those values and see how it works out. You will still need to use speedbrakes for fine tuning, unforecasted conditions, etc...

 

You are right, i have seen that when i'm descending with tailwind, the aircraft go off path and i have to apply speed brakes to go back on path.

[WebMaximus 372]

Thanks again guys for lots of great input and tips, I'll take all good advice with me and hopefully that will help me lessen the use of speedbrakes.

[Spin737 102]

240 or less and to keep below this speed my decent rate at idle thrust and with fully extended speed brakes is approx 1200 feet/min often resulting in coming in too high.

You should be closer to 2200fpm at 240knots with S/B and clean.

 

The NG can overspeed/go to VNAV SPD at the TOD above FL350.

[WebMaximus 372]

Exactly and that's what makes me wonder why my NGX most of the times won't do more than approx 1200 ft/min regardless of head or tailwind. One thing though is of course the use of TAI on most flights this time of year in Europe where I do most flying.

[Lek767 37]

One thing though is of course the use of TAI on most flights this time of year in Europe where I do most flying.

 

Something I noticed when using engine anti-ice is that when switching it off again (for example when breaking through the clouds or when outside temperatures are high enough), engine thrust does not return to flight idle, but stays at the slightly increased level associated with the use of TAI. Only when I tap F1 or wiggle my physical throttle a bit (that sounds wrong, I know), and then fully close it again, does the N1 thrust return to its normal value. This might be affecting your flights as well, possibly.

[FirstOfficera320 1]

Hi Richard,

 

I just did a test flight from LAX to SFO using the 738WL, the most slippery of them all. I flew 20nm past the T/D at FL390. 115 track miles I started the decend. No speed brakes and I used V/S -3000fpm. No trouble all the way down, although I remained from 1500 to 2500 feet above the VNAV profile. Despite this I was still stable at 1800AGL on the ILS.

 

I find VNAV leaves me conservativly low. Still, with proper energy management (Kinetic (speed), Potential (Altitude) and Chemical (fuel)) it's not that hard to manage. Just stay ahead of the aircraft and meet the gates. Plan to be at FL100 and 250kts at 40 track miles to the runway. 15 Track miles should be 3000 agl. and slowing towards Vapp.

[WebMaximus 372]

 

Something I noticed when using engine anti-ice is that when switching it off again (for example when breaking through the clouds or when outside temperatures are high enough), engine thrust does not return to flight idle, but stays at the slightly increased level associated with the use of TAI. Only when I tap F1 or wiggle my physical throttle a bit (that sounds wrong, I know), and then fully close it again, does the N1 thrust return to its normal value. This might be affecting your flights as well, possibly.

 

Very interesting you mention this because I've noticed that too and on occasions this fact has tempted me not to use TAI especially when it still won't do any real difference in FSX where no icing conditions are simulated at least not with the NGX but trying to fly as close to real world ops as possible it still feels wrong not using TAI flying in conditions where you would IRL.

 

This can't be totally correct or is it like this in the real bird too?

 

Hi Richard,

 

I just did a test flight from LAX to SFO using the 738WL, the most slippery of them all. I flew 20nm past the T/D at FL390. 115 track miles I started the decend. No speed brakes and I used V/S -3000fpm. No trouble all the way down, although I remained from 1500 to 2500 feet above the VNAV profile. Despite this I was still stable at 1800AGL on the ILS.

 

I find VNAV leaves me conservativly low. Still, with proper energy management (Kinetic (speed), Potential (Altitude) and Chemical (fuel)) it's not that hard to manage. Just stay ahead of the aircraft and meet the gates. Plan to be at FL100 and 250kts at 40 track miles to the runway. 15 Track miles should be 3000 agl. and slowing towards Vapp.

 

Thanks for your tips and interesting feedback!

 

When you say you used V/S descending @ 3000 ft/min were you also able to do that below 10k keeping the speed below 250 knots?

 

I heard before the 800WL is the most slippery one and I do all my flying in that model so guess that's adding to my problems coming in too hot on many approaches.

[WebMaximus 372]

 

Something I noticed when using engine anti-ice is that when switching it off again (for example when breaking through the clouds or when outside temperatures are high enough), engine thrust does not return to flight idle, but stays at the slightly increased level associated with the use of TAI. Only when I tap F1 or wiggle my physical throttle a bit (that sounds wrong, I know), and then fully close it again, does the N1 thrust return to its normal value. This might be affecting your flights as well, possibly.

 

Just replied but looks like it was never published so forgive me if this will end up as a double post.

 

Interesting you mention this because I've seen the same thing and this has in fact on some occasions almost had me skip using TAI although I've been in conditions requiring it to avoid having this extra thrust even after turning TAI OFF especially knowing icing isn't modelled in FSX/NGX but it still feels wrong when trying to fly the NGX as close to real world ops as possible.

 

Not sure if my memory serves me right now but I think I read somewhere once an explanation to this behavior, can't remember though if the explanation was why it is like this in only the NGX or also in the real aircraft.

[Vagabondo 23]

NGX seems to be a bit inconsistent. It seems OK to me, but judging by these forums others seem to have very shallow rates of descent.

 

A buddy of mine who flies the NG in real life told me once that his company even flies almost whole descends and approaches with ILDE thrust, from FL380 down to the runway.

That is absolutely normal or any and every airline flying any kind of jet airliner. Most airlines SOP say that one just have to be stable by 1000 (or 500 VMC). By stable, that means configured with normal thrust on the normal flight path with a normal speed.

 

Ok, but with thrust at idle and speedbrakes fully extended is a 1000-1200 ft/min descent rate realistic?

Only for clean speed.