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tonymerry

737 Overspeed on descent

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The 737 is impossible to keep to a set speed, i.e. 250 knots, if the rate of descent is anything much above 1600 fpm. This is with the spoilers up & pressing F1 to ensure throttles are fully back. I am sure that the real 737 is not that slippery, as on Flight radar you can see them descending at up to 2000+ fpm. Does anyone else suffer from this problem or am I not doing something right?

Tony merry

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 or am I not doing something right?

 

It's more likely that you're not doing something right. As far as I'm aware, the sites you're citing do not give you aircraft configuration data, so you're not seeing how they've managed their energy, and how they're using drag to assist them in the descent.

 

Can you be more specific about what you're expecting, and how you're operating the aircraft?

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The 737 is impossible to keep to a set speed, i.e. 250 knots, if the rate of descent is anything much above 1600 fpm. This is with the spoilers up & pressing F1 to ensure throttles are fully back. I am sure that the real 737 is not that slippery, as on Flight radar you can see them descending at up to 2000+ fpm. Does anyone else suffer from this problem or am I not doing something right?

Tony merry

 

I encountered same issues so I'm beginning my descent about 30nm from TOD manually adjusting V/S to match FMC rate. At around 15000 I start slowing down which allows me to get 1400/1200 fpm before I hit 10000 which at that point is easy as I'm cruising at around 245 and speed is easly controlled by flaps/spoilers/gear.

 

Dunno if it is the right way lol but works for me :)

 

Paul Grochowski

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As far as I am aware I am operating more or less by the book. Using the FMC to control the descent. But to give you an example, try the flight from ENBR to ENTC, the final approach is via TULDA at 12000ftA then 9 miles to UMSEG at 6000ftA then  to ETUTU at 5000ft and 11 miles to the runway 01 at 77ft. During all of that descent the spoilers were fully deployed, but it was impossible to keep the speed below 250 knots under 10000ft. and impossible to get the speed down to 150kts for landing. That is the sort of thing I am referring to.

Your comment will be appreciated.

Tonymerry

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Welcome Tony.

 

What was the wind speed and velocity on your approach?

 

I seem to remember two independent real world pilots for two seperate airlines rated on the 737NG saying that the NGX seems to be more 'slippery' than its real world counterpart. That's more a simulator thing and not the NGX's fault I think but that is besides the point as from my experience you can easily meet height and speed restrictions with proper descent planning and careful manipulation of the different modes of autopilot/FMC.

 

I'm confident you will eventually be able to manage energy throughout the descent with more practice. I suggest becoming familiar with VNAV, LVL CHG and VERT SPEED. YouTube, an AVSIM search and Google are also good sources for information on descent management techniques.

 

PS

I guess some pilots accept the speed increase that comes with a 2000+ sink rate with the forward view of having a 'level segment' or similar planned somewhere along the way where they can throw the Speedbrakes up and bleed the speed off. That would be one of many techniques that could've been in use on the flight you're referencing in your first post.

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I think it all comes down to planning.

Sand in the gears is when you don't know the runway you're going to land on with calm winds - and you can't get ATIS until after descent has begun... and find that the runway that's active should had you descending earlier... so you're going to have to get into a holding loop or something to get down.

 

But perhaps if I've planned better and assumed the tight approach that wouldn't of happened.

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 That particular transition on the AMIMO7W star does hold you up much higher than the others. That being said, it also gives you plenty of time to slow to cross UMSEG at 220kts or less even. It all comes down to the planning, and having to chase your speed on an already steep approach (I recall seeing 3.7-4 degrees) will often lead to practice for the go around.

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I know the 800, and maybe the 900 to some extent, are more slippery than the 700 and 600. Or at least as far as

the PMDG sim.. I fly the 700 the most, and it seems normal to me. And if I switch to the 800, I do notice I have to plan

for a little extra slipperyness in comparison.  But the real worlders generally say the same thing when comparing the 700

and 800. The 600 is the least slippery of all, and is easy to get slowed down. I'm sure part of that is the lack of winglets..

I've never tried any of the longer model non winglet versions. To me, the 600 feels like a 500 with a glass cockpit.

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A B737 rated pilot who contributes here has mentioned that speedbrakes are required on about half of his descents.  My opinion on the deceleration to 240 and descents is that drag is required at any descent above 900 fpm so plan the speed decrease at 10000 such that the green banana is couple of miles before the 10000 constraint. This is what VNAV does if you watch it.

 

Agree with the 800 being slippery compared to the 700, and now that SWA has a few I've started spending a lot more time in it and am enjoying it.

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The 737 is impossible to keep to a set speed, i.e. 250 knots, if the rate of descent is anything much above 1600 fpm. This is with the spoilers up & pressing F1 to ensure throttles are fully back. I am sure that the real 737 is not that slippery, as on Flight radar you can see them descending at up to 2000+ fpm. Does anyone else suffer from this problem or am I not doing something right?

Tony merry

 

Out of interest which descent mode are you using for example VNAV, maybe V/S or even FL change?  If it is VNAV do the speeds on the legs page look like the STAR descent profile?

 

I found in the past having the anti ice on didn't help.

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Some time ago another pilot posted a video (youtube) and used to speed instead of slowing with speed brake.

He was from Canada and is used to operate the NG this way.

At the top of descent it start to accelerate the descent using 300-310 IAS with speed INT, once near  the 10000 ft it start to slow down, by set speed below 250.

The important thing is to be below the vertical flight path computed by the FMC , you can always check in the ND where the arc will bring you by setting your desired FL.

This is the only way even using antiice which is problematic to slow down the 737.

ATC want that you do your homework before and not in crossing FL100.

In some approach you could also have 220 IAS restriction .

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The NGX is pretty accurately modelled and is very slippery in real life, especially if you need to” go down and slow down”. Again this is based on my own companies SOP’s and different operators have different ways, this is only guidance.

Descent as is with any commercial aircraft is primarily about one thing, energy management and getting the aircraft safely configured at the correct speed for landing and the planning for that starts from TOD. Here’s the basics from TOD.

Firstly work out your expected track miles to landing, approximately x3 your altitude works out really well. Eg 30,000ft = 90nm.

Allow extra distance to reduce to approximately 200kts 10nm from landing, (add 1nm for every 10kts of deceleration). For every 10kts of Tailwind also add 1nm.

 

Some time ago another pilot posted a video (youtube) and used to speed instead of slowing with speed brake.


During the initial phase of descent (above 10,000ft) by far the most effective way to regain profile is to increase IAS, right up to 330kts. You can either recapture the profile at your planned speed in the FMC or update the new descent speed in the FMC to recalculate a new descent profile. If this still leaves you high then use speedbrake. 300kts + speedbrake gives you a pretty impressive descent rate. Especially when accelerating to that speed and it’s not uncommon to see -4000fpm or more!

In real life there are so many variables thrown in. Weather, ATC, shortcuts and traffic to name a few, you have to plan around that. There are very few descents where we’re sat on our hands watching the aircraft descending on the FMC’s planned profile at the correct speed!

 

As I've also mentioned on a post here previously we do not use just LNAV and VNAV, treat the MCP as a toolbox, use whatever mode you need to get the job done!

 

That particular transition on the AMIMO7W star does hold you up much higher than the others. That being said, it also gives you plenty of time to slow to cross UMSEG at 220kts or less even.

 

Exactly how it’s done, a large proportion of restrictions on STAR’s will leave you high and the most effective way to deal with it is to remove energy from the aircraft by reducing speed. If you do nothing about it VNAV will show you’re on profile (based on the restriction) and once passing it you’ll see the VNAV profile somewhere 4000ft below you, FMC drag required etc. A great way during planning is to temporarily delete the ALT restriction in the FMC. This will show the ALT at which the aircraft would like to be at if the restriction wasn’t there.

Once below FL100 you are limited to 250kts so initially speedbrake should be used initially to increase your ROD.

If you still need more drag the next effective configuration is to reduce to 220kts, use Flap 5 w/speedbrake. (2300fpm ROD)

If you’re still looking high and getting close to the point you need to reduce speed for landing reduce to 180kts, use flap 10 w/speedbrake (1500fpm ROD or roughly 500ft/nm)

After that consider a hold or in real life we could request extended vectors.

The final phase of approach regarding descent management is governed by very strict criteria regarding stabilised approaches by our landing gate (500ft VMC, 1000ft IMC) and a go-around is mandatory if not correctly configured at the correct speed.

We use the 3,2,1 rule at 10nm = 3000ft AGL, 200kts and Flap 1 (our SOP’s states we must have at least F1 by 10nm) If this criteria isn’t closely met you’re going to have a hard time configuring the aircraft for landing.

I hope this information helped and as I always stress, is based on my operators SOP’s and taught during line training.

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Don't forget the winds during descent !! if you do not adjust them in the FMC they will prevent the FMC from carrying out its plans. Sometimes during descent there is unaccounted for 50 kt tailwinds and they will eat terrain quickly for you. You can intervene the speed to 330 kias if need be or use LVL CHG (idle power descent) and set the speed in the MCP.

 

Lastly, make sure that you are at idle power indeed. Controllers have to be well calibrated. Sometimes the throttles don't quite get you there.

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