Correct Go Around Procedure

[threexgreen 3,139]

On 11/12/2018 at 3:28 AM, trisho0 said:

Thanks Niklas good advice. I had again the same FMC message Des Path Unachievable" and I armed speedbrake. The 737NG started descending and when I was around the Altitude according to FMC on the actual waypoint I disarmed Speedbrake. I didn't have "Drag Required" message. So, from FMC I saw the T/D close to 10NM I started preparing Flaps 1, speedbrake, Flaps 2, etc I was be able to land (ILS).

I will try with 747 or T7 and see if I get the same DPU message from FMC. Maybe the 737NG is more sensitive (lol).

That message shouldn't pop up so much. It happens sometimes but usually it's following the path just fine. What's your descent profile and do you edit the speeds and altitudes for the route yourself? Do you fill out the descent forecast page?

[trisho0 23]

51 minutes ago, threegreen said:

That message shouldn't pop up so much. It happens sometimes but usually it's following the path just fine. What's your descent profile and do you edit the speeds and altitudes for the route yourself? Do you fill out the descent forecast page?

From FMC I don't change legs info but adding and or removing waypoints accordingly and usually following some from Simbrief flight plan. I don't edit speed/altitude from legs. Never touched forecast, don't know how it works.

[threexgreen 3,139]

23 hours ago, trisho0 said:

Never touched forecast, don't know how it works

There you go. This is most probably what's causing most of the DPU messages. Most crucial on that page is the descent wind data. This is one of the factors involved in calculating the descent path. If you don't fill that out winds cannot be put into the mix for descent path calculation and DPU messages are likely to pop up because the descent path doesn't account for winds that are affecting the aircraft's performance on descent.

There is also an entry for the altitudes at which you plan to use engine anti-ice during descent since anti-ice affects the engine's performance. You can also enter the ISA deviation (ISA is 15°C at ground level) and the pressure at your arrival airfield.

[trisho0 23]

1 hour ago, threegreen said:

There you go. This is most probably what's causing most of the DPU messages. Most crucial on that page is the descent wind data. This is one of the factors involved in calculating the descent path. If you don't fill that out winds cannot be put into the mix for descent path calculation and DPU messages are likely to pop up because the descent path doesn't account for winds that are affecting the aircraft's performance on descent.

There is also an entry for the altitudes at which you plan to use engine anti-ice during descent since anti-ice affects the engine's performance. You can also enter the ISA deviation (ISA is 15°C at ground level) and the pressure at your arrival airfield.

How can I work with that? It has to be an advanced setup for the FMC. I will need to find the data info to enter accordingly I guess ….

[vhufo 35]

14 hours ago, threegreen said:

There you go. This is most probably what's causing most of the DPU messages. Most crucial on that page is the descent wind data. This is one of the factors involved in calculating the descent path. If you don't fill that out winds cannot be put into the mix for descent path calculation and DPU messages are likely to pop up because the descent path doesn't account for winds that are affecting the aircraft's performance on descent.

There is also an entry for the altitudes at which you plan to use engine anti-ice during descent since anti-ice affects the engine's performance. You can also enter the ISA deviation (ISA is 15°C at ground level) and the pressure at your arrival airfield.

Funny this has come up because i have been studying this a bit over the last month.

 

The 737 is a beast to slow down, and I've been trying to find a method which results in a smooth descent using minimal, if no speed-brake at all.

 

Using the exact method as described above i found has had minimal impact on the aircraft's behaviour. I have input the wind data, then as the aircraft has passed through those altitudes have recorded the input data against the actual wind direction and speed. On most occasions the data has been very close, yet the aircraft cannot maintain airspeed, it will always over-speed past the FMC descent speed, and this is no matter whether the aircraft is light or heavy.

 

The method i have ended up using is applying all the data as required, ie, descent forecasts, speeds etc. but starting the descent 15 to 20 miles early using LVLCHG, that's of course there are no altitude restrictions on descent, of which mostly occur at lower levels. The aircraft descends nicely maintaining the descent forecast speed without a problem. You have to be careful though at the start of the descent. If the IAS is lower than the programmed descent speed in the FMC, using LVLCHG the aircraft wants to dive, so i just slowly increase the speed in the autopilot until it matches the programmed descent speed so it maintains a descent rate of around 2500ft per minute.

 

Usually the VNAV Path catches up near 10000ft, of which by that time I've got the aircraft established speed wise, whether it be for a near or far side approach, and switch to VNAV Path then to meet the altitude restrictions which are generally at the lower levels.

 

I just wanted to find a better way to manage the speed on descent because using the speed-brake continuously is not something the passengers would enjoy, and to find a better way to set the aircraft up for approach instead of fighting the speed all the way down. 

 

If anyone can let me know why the aircraft continues to speed up past the FMC programmed speed using VNAV Path i'm all ears. But I'm pretty sure I've got all the parameters covered, could be wrong though.

 

Andy Baird 

Edited November 15, 2018 by vhufo

[trisho0 23]

5 hours ago, vhufo said:

I have input the wind data

Where do you find the wind data for insertion into FMC?

[MarkJHarris 128]

Interesting. 

OK. Try these things. As a quick check, aim to be back to 210kts at about 11nm at the latest. If you are not slowing to reach 200kts by 10nm, 190 by 9, etc. then do something about it right away.

On a 737, the speedbrake is not a "stick of Shame" It's essential! So use it.

You should on an ECON pre-programmed descent, be able to wind down the MCP Alt and it should retard at TOD and glide all the way down to the approach. It should perform a CDA with little effort. You do need to make sure you program the FMC correctly though.

 

Usually a mid life aircraft will fall short on speed during the descent and need a bit of power. New ones, slightly less but again, often it will descend on profile and speed will fall a bit short. Flap 2 is a bit of an aberration. It's just not used in real life. Try to let the speed decay at least 20kts below limits to take 1, and 5. you can use speedbrake upto Flap 10, but NOT Flap 15 or more. Verboten! If you need to slow down, taking gear early is preferred, and works well.

Remember the FMC calculates vertical path back from the top of the approach up to TOD. It's a case of Rubbish in-Rubbish out usually. if it doesn't do what you thought, it's because you've done something to cause this. Enjoy!

[threexgreen 3,139]

20 hours ago, trisho0 said:

How can I work with that? It has to be an advanced setup for the FMC. I will need to find the data info to enter accordingly I guess ….

I use PFPX for flight planning and it gives me descent winds that I put into the FMC. Does simbrief not include descent winds or altitude winds?

8 hours ago, vhufo said:

Funny this has come up because i have been studying this a bit over the last month.

 

The 737 is a beast to slow down, and I've been trying to find a method which results in a smooth descent using minimal, if no speed-brake at all.

...

That's weird. I rarely ever get a DPU message and I also don't have to use speedbrakes so much. It usually works just fine. What's your typical descent profile and what are your typical altitude/speed restrictions on the STARs you fly?

Other than LVL CHG, you can also select 'Descend now' on the descent page before TOD and it will start to descend at 1000 fpm until capturing VNAV path.

1 hour ago, MarkJHarris said:

Usually a mid life aircraft will fall short on speed during the descent and need a bit of power. New ones, slightly less but again, often it will descend on profile and speed will fall a bit short.

Why do mid life aircraft behave differently than newer ones in that aspect?

[trisho0 23]

6 hours ago, MarkJHarris said:

OK. Try these things. As a quick check, aim to be back to 210kts at about 11nm at the latest. If you are not slowing to reach 200kts by 10nm, 190 by 9, etc. then do something about it right away.

On a 737, the speedbrake is not a "stick of Shame" It's essential! So use it.

I just learned that and it worked for me.

[trisho0 23]

6 hours ago, MarkJHarris said:

Usually a mid life aircraft will fall short on speed during the descent and need a bit of power. New ones, slightly less but again, often it will descend on profile and speed will fall a bit short.

Because of the engine age?

[trisho0 23]

6 hours ago, MarkJHarris said:

Try to let the speed decay at least 20kts below limits to take 1, and 5. you can use speedbrake upto Flap 10, but NOT Flap 15 or more. Verboten! If you need to slow down, taking gear early is preferred, and works well.

I didn't use flaps but speedbrake (SHIFT+/) or simply "/" until the Altitude becomes as expected. Am I wrong?

[downscc 1,327]

On 11/15/2018 at 6:34 PM, trisho0 said:

I didn't use flaps but speedbrake (SHIFT+/) or simply "/" until the Altitude becomes as expected. Am I wrong?

Context?  During descent on the arrival  or in the terminal area lining up for final?  Depends.  Once flaps and gear are hanging out in the wind you don't want to have to retract them... not problem retracting speedbrakes.  So,,,, it depends. 

[trisho0 23]

5 hours ago, downscc said:

Context?  During descent on the arrival  or in the terminal area lining up for final?  Depends.  Once flaps and gear are hanging out in the wind you don't want to have to retract them... not problem retracting speedbrakes.  So,,,, it depends. 

Yes, when just descends started if it doesn't going down the Altitude and only when the message FMC message Des Path Unachievable I apply speedbrakes

[MarkJHarris 128]

When a 737 is delivered new, the FMC has a fuel factor applied in one of the PERF pages to adjust it's economy and fuel burn performance. Invariably, it's 0.0.

As aircraft age, the company will monitor fuel burns and adjust this factor as the aircraft ages. Typical mid-life figures are 5.5-5.8.

Mid life is a quaint term. New Aircraft are either bought (you usually mortgage over a 17 year term) or leased (typically 10 years). Accountancy procedures for depreciating assets are the reason. (It's beyond me- I just fly them!!). Often, the folk buying the aircraft on finance then lease it so it's paid off over 10 years and they can then sell it for profit after it comes back or re-lease it, etc. My firm, (no guesses please) bought a load of brand new aircraft last couple of years, as no 10 year old ones were available. Now with MAX deliveries coming, there is an ample supply of 10 year old aircraft looking for new homes. 

Anyway, the point is that this fuel factor is a combination of increased fuel flow due to aging engines, and more draggy airframes. All aircraft get heavier as they get mods, damage repairs and layers of paint. Boeing paint is excellent, but you typically repaint after 5 years (adds weight) and at the end of the lease, strip it right back to primer and paint white. Second owner then has to paint it in their colours and it will be over the white and therefore heavier than new.

 

When the NG came out, GPS was only just becoming more common so some didn't have it. Many don't have HF, only one ADF and no ACARS. No tiller on the right either. Early ones didn't have armoured flight deck doors, nor TV screens for access. Winglets were also not standard. Things like sun screens were just unnecessary luxuries. Later aircraft may have all these and earlier ones have had many fitted as modifications.

Actually finding two the same is quite hard. We've now got 34 identical ones, the rest are real Bitsa's!

That's the explanation of the term Mid-Life.

However, they all have that factor in the FMC, so in practice, when you wind down the MCP ALT window, in LNAV/VNAV on a standard programmed arrival it should start down in idle and deliver you to the ILS on glideslope and speed. Without speed brake and any intervention. (I forgot- quite a few mid lifers don't have speed or Alt intervention either!).

 

 

 

[trisho0 23]

2 hours ago, MarkJHarris said:

When a 737 is delivered new, the FMC has a fuel factor applied in one of the PERF pages to adjust it's economy and fuel burn performance. Invariably, it's 0.0.

As aircraft age, the company will monitor fuel burns and adjust this factor as the aircraft ages. Typical mid-life figures are 5.5-5.8.

So, this is something we can adjust in the FMC right?