Hi all,

 

Which is the usual or "correct" method of slowing down while descending:

- Slowing down by deploying flaps and letting the aircraft reach the respective speed targets, or

- slowing down by manually reducing the speed through the MCP.

 

Is either method subject to pilot preference or company policy?

 

Thanks,

Christos

Hi Christos,

 

Generally, you can't go down and slow down at the same time.

 

Especially true in the NGX.

 

I have many hours logged in 737NG and 777 full motion simulators and I've never deployed flaps to slow the airplane.

 

If I need to bleed off excess airspeed, I level off a bit and kick out the speed brakes. Just ensure they're stowed by the time you're ready to deploy your flaps and you should be in the slot without a problem. The airplane will slow fast when you're level, with idle thrust, and the speed brake out.

 

Cheers.

Hi all,

 

Which is the usual or "correct" method of slowing down while descending:

- Slowing down by deploying flaps and letting the aircraft reach the respective speed targets, or

- slowing down by manually reducing the speed through the MCP.

 

Is either method subject to pilot preference or company policy?

 

Thanks,

Christos

 

Well you would put the speed you want into the MCP, but then it's a matter of getting to that speed. If you level off and deploy speed brakes you can bleed off over 70kts in less than a minute. Below 250kts you could use flaps to help slow you down. The landing gear (sometimes referrred to as an anchor by pilots) is also a very efficient method for ldropping speed.

Slowing down can get hard in certain weather conditions. FL/CH and Speedbrakes are normally my best friends during descents. Sometimes it's up to you and your knowledge whether you need to take speed over altitude or altitude over speed. Takes getting used to the Aircraft and sure your descent plan is sufficient.

 

Say you're on a base leg and ATC ask you to reduce 180knts and you indicate around 200 then you can actually use flaps to slow down, as long as you are NOT above the flap limits - but this varies on your altitude goals and speed.

 

Get to know your aircraft, in different situations and you'll know when to use what :-)

I'd consider it poor technique in most situations to use the flaps to slow down. It could put you closer to the flap speed limits (which could cause damage if you bust them), and there's a noticeable balloon/pull that the passengers would feel.

I tend to level off a bit let speed bleed off and as the speed drops extend flaps (well below their limits and only done as nearing the airport), then when you continue to descend you can achieve a more rapid descent without gaining speed due to the flaps and get back on path. But really I let VNAV judge it most the time, I may make some adjustment if their is unexpected tail winds or long periods of anti ice but I usually don't have any issues and rarely need to use the speedbrakes.

 

If i am at higher alts and am off path I usually increase speed which increases descent rate, overshoot the VNAV path and bring back my speed, in the end I am back on path or even below it. This helps me bleed off even more speed if I wish without use of speed brakes or anything.

Indeed the 737 NGX, because of the wing design I believe and I stand to be corrected on this, is a very slippery airplane and the manual sugests "aggressive speed management".

 

I also use a combo of level flight and speed brakes to slow the aircraft down a bit. But again, this will depend on weather as a strong tail wind can seriously upset your vertical profile LOL!

 

Regards

What works best for me, is descent via FLCH (If I'm using ATC, which I usually do, else I use VNAV) at 287kts (Descent rate at CI of 40 on the NGX) down to FL200 then down to 270kts to 10000 , with or without spoilers, below that 220kts, 180 on final approach, at localizer capture 160kts down to VREF +5kts to touchdown.

Using the speedbrake to deccelerate is not a good practise, you spill valuable energy and stress the aircraft in the long term. At least this is what my best mate says who is a real world A330 pilot.

 

What I do is this: try to start my descent from climb flight level as late as possible. Cut the throttle to idle and start descending until 11000 Feet, which is where ATC usually instructs me to. After this, level off and let speed die to below 250, so that I can start descending below 10000ft. I try to use the flaps as late as possible too, around 3-4000ft, just before final.

 

My target is to try to descent from climb altitude to runway using no speedbrake, late flaps and as less throttle as possible. This is what good energy management is about according to this friend of mine

I also remember a real world 747 pilot who commented on the question about the up and down pitching of the 744X during descent, which did not happen on the FS9 version, that they had actually been taught to start their descent early on VS or the VNAV SPD mode and then catch the glide path on their way down.

 

An interesting thing about the the NG, and this is what I saw on a 737-700 cockpit video is that the initial descent from cruise level is VERY steep, somewhere in the region of 5500 fpm. I believe the video was taken from a Quatas flight.

 

Regards

Bear in mind that when using flaps you have to take note of minimum and maxiumum flap retraction speeds and extension speeds. Also there are usually altitude restrictions. The VC10 has flap isolate switches selected on the climb check and approach check specifically to prevent flaps deployment.

There was one a/c that did use flaps to slow down and that was early versions of the Caravelle. After they lost a few wings in flight everything changed!!

Using the speedbrake to deccelerate is not a good practise, you spill valuable energy and stress the aircraft in the long term. At least this is what my best mate says who is a real world A330 pilot.

 

I think this is more to pilot preference or company specific policy, most planes Ive been on has used spoilers at some point during descent.

StarSailor79, on 17 August 2012 - 11:28 AM, said:

Using the speedbrake to deccelerate is not a good practise, you spill valuable energy and stress the aircraft in the long term. At least this is what my best mate says who is a real world A330 pilot.

 

You are not correct here! Simply throttling back will slow the a/c down, but adding speed brakes will reduce speed much more quickly. Quite often ATC will require a rapid speed reduction.

Speed brakes are also a necessity in an emergency dive for example. Also where a large loss of height is needed very quickly. An example of that would be the approach to Torino where it is necessary to descend from FL220 to 4,000ft very quickly indeed. And no they don't stress the a/c. If the a/c does reach an overspeed condition in spite of speed brakes being deployed then they will blow back to say 25%.

What you don't do of course is to select speed brakes while under power. That's similar to your car braking and accelerating at the same time.

Your friend I would suggest needs a check-ride! If what your friend says were true then speed brakes would be so dangerous as to not have them fitted at all!!

You are not correct here! Simply throttling back will slow the a/c down, but adding speed brakes will reduce speed much more quickly. Quite often ATC will require a rapid speed reduction.

Speed brakes are also a necessity in an emergency dive for example. Also where a large loss of height is needed very quickly. An example of that would be the approach to Torino where it is necessary to descend from FL220 to 4,000ft very quickly indeed. And no they don't stress the a/c. If the a/c does reach an overspeed condition in spite of speed brakes being deployed then they will blow back to say 25%.

What you don't do of course is to select speed brakes while under power. That's similar to your car braking and accelerating at the same time.

Your friend I would suggest needs a check-ride! If what your friend says were true then speed brakes would be so dangerous as to not have them fitted at all!!

 

I think you're mis-understanding what he mean't, he clearly said "energy management" and didn't say they were dangerous. For the most part it is good not to use them for passsenger comfort if not really necessary. However, they are fitted to the aircraft to be used so if you need a rapid descent they can be used.

Hi Christos,

 

Generally, you can't go down and slow down at the same time.

 

Especially true in the NGX.

 

I have many hours logged in 737NG and 777 full motion simulators and I've never deployed flaps to slow the airplane.

 

If I need to bleed off excess airspeed, I level off a bit and kick out the speed brakes. Just ensure they're stowed by the time you're ready to deploy your flaps and you should be in the slot without a problem. The airplane will slow fast when you're level, with idle thrust, and the speed brake out.

 

Cheers.

 

In addition to this, I think it's possible to descend earlier with a much gentler glide slope, thus allowing better control of speed during descent. I may be wrong, though.