I have always wondered why the FMC pop ups a " Drag Required " warning .I assume it's cause of the wind changing but even if it was like that I guess the real time reaction of the FMC should allow immediately to auto-reset the remaining vertical route accordingly to the wind changing, just like the LNAV does when lateral wings injects.The LNAV does not ask to the pilot to turn a few degrees to correct the wind intervention so why the VNAV does that instead ?Thx

When in VNAV the descend will be done by default using descend path.This path must be done by remaining in a certain speed limits, FMC will calculate the path with aerodynamics of the plane and standard air, but in case of tail wind for example, to mantain the path the aircraft will receive less drag from the plane itself, so it means that the aircraft accelerates.The airplane itself has no way to slow down in path mode.The aircraft vertical speed is locked to remain in path, the throttles are in idle for the descend, so the only thing it can do is to warn you that it is unable to mantain speed, and if you want to do manually you need to brake manually (speed brakes are manual in flight)There is a way to let the aircraft do a descend without using speed brakes: using SPD DES, with this the aircraft will descend like in Level Change mode, disregarding the descend path but following speed and altitude restrictions.However, if the aircraft is unable to slow down you risk to not be able to reach the next altitude on the flight plan, the aircraft to slow down will reduce the descend rate. So, you cannot reach for example the approach altitudes. Also remember that SPD mode is less economical than path mode.To prevent problems you need to fill the des forecast page, in tis way the aircraft BEFORE DESCENDING have an idea on what winds will encounter, it will adjust the TOD and the path to reduce or eliminate the use of the drag (that is less economical)

To prevent problems you need to fill the des forecast page, in tis way the aircraft BEFORE DESCENDING have an idea on what winds will encounter, it will adjust the TOD and the path to reduce or eliminate the use of the drag (that is less economical)

I will follow your suggestion but a question surfaces, why does the forecast does not auto fill itself and the VNAV path as well f.i. 30 nm before the T/D ?

Because the aircraft is not yet equipped with this things of automatic update. Same for most of the real one. There are projects on the real one to give the possibility to update costantly the forecasts, but is a project as far as I know.If you want to be sure to limit the drag required, without knowing the wind information, try to put a fictional tail wind on the forecast, it will help you, also if winds are not present.

I have always wondered why the FMC pop ups a " Drag Required " warning .I assume it's cause of the wind changing but even if it was like that I guess the real time reaction of the FMC should allow immediately to auto-reset the remaining vertical route accordingly to the wind changing, just like the LNAV does when lateral wings injects.The LNAV does not ask to the pilot to turn a few degrees to correct the wind intervention so why the VNAV does that instead ?Thx

Because the systems don't allow to deploy spoilers (or gear) automatically.

The FMS has no knowledge of winds en route or forecast during the descent phase. With an ACARS system in place, one might be able to upload weather data from a source such as ASE, but you would be required to have an accurate flight plan in ASE with the respective wind data at altitudes at each waypoint. I imagine programming some sort of ACARS would be a mammoth task, and it would require simconnect or FSUIPC or something. I do not have the knowledge or expertise to say whether this is possible or not. Cool it would be, some sort of data uplink. But if you have ASE or similar, it is not much of a deal to enter a few lines of forecast data on the descent forecast page via the CDU. Andrew

If you want to be sure to limit the drag required, without knowing the wind information, try to put a fictional tail wind on the forecast, it will help you, also if winds are not present.

This is a great trick indeed, 10-15 kts of wind would be enough ?Anyway a consideration, if also in the reality it works like that, why in the reality ( at least in my 50 flights I have done as passenger in my life ) it is not so common to apply speed brakes ?When I run 737 NGX pretty much each flight I am forced to apply 4-5 times the speed brakes while in the reality I see it happens only every 2-3 flights instead.

You can try it.What you need to know is that if you put winds that will be not present, the flight will lose its economy, the descend is calculated to use less thrust as possible, if you put tail winds, and winds will not be present, the aircraft will need to use thrust to mnatain the path.So, if you need to save fuel, use correct data, if you want to spend more (FS fuel is free) use any value you want in the forecast page.

This is a great trick indeed, 10-15 kts of wind would be enough ?Anyway a consideration, if also in the reality it works like that, why in the reality ( at least in my 50 flights I have done as passenger in my life ) it is not so common to apply speed brakes ?When I run 737 NGX pretty much each flight I am forced to apply 4-5 times the speed brakes while in the reality I see it happens only every 2-3 flights instead.

"why in the reality ( at least in my 50 flights I have done as passenger in my life ) it is not so common to apply speed brakes ?"During a flight ATC will tell you what to do and when to start doing it. For separation etc. various reasons. In some cases it (drag) is required to comply with ATC.Slow down, plan this .. expedite descent (drag) at requested speed (drop like a rock but do not increase speed), advise if unable.And you are listening to ATC vectoring aircraft ahead of you ... so you kinda know what's next up for you!

In VNAV the A/P will maintan the vertical profile. If while doing this, the SPEED increases (I think it's 10kts) above bugged speed, you'll get the drag required message.If you're having trouble slowing down, check this out: http://forum.avsim.net/topic/344559-do-you-really-need-speedbrakes-video-part-2/

You must remember there are few passenger airplanes out there with wings as efficient as the NG. It behaves as a big glider. So you will indeed often see spoilers being deployed to aid in descent. In my country, some of the STARs are very poorly planned by the aviation agency, and it is very common to see spoilers being deployed for a good portion of the descent. There is one descent into Rio de Janeiro that dives so steeply into the final approach segment that you will see 737s deploying the landing gear, flaps, ans spoilers as high as 8000' to comply with the restrictions.

There is one descent into Rio de Janeiro that dives so steeply into the final approach segment that you will see 737s deploying the landing gear, flaps, ans spoilers as high as 8000' to comply with the restrictions.

Gear at 8000 ? Is that a rollercoaster STAR ?

Gear at 8000 ? Is that a rollercoaster STAR ?

Pretty much. Check it out. http://www.aisweb.ae...wy-15-star-.pdfIn a certain Brazilian company´s SOP for the NG series they recommend all approaches coming in from the North to fly with gears down, spoilers in flight detent and at 220k (or less if able) from 7000' down and only retract spoilers with flaps 5 or lower. Previous to this recommendation lots of crews were reporting unstabilized approaches resulting in go-arounds. Planes were coming in high and hot. Try it and you´ll see what I mean. With FS9´s NG I had enough trouble flying this star, with the NGX it´s a real challenge to say the least!

Pretty much. Check it out. http://www.aisweb.ae...wy-15-star-.pdfIn a certain Brazilian company´s SOP for the NG series they recommend all approaches coming in from the North to fly with gears down, spoilers in flight detent and at 220k (or less if able) from 7000' down and only retract spoilers with flaps 5 or lower. Previous to this recommendation lots of crews were reporting unstabilized approaches resulting in go-arounds. Planes were coming in high and hot. Try it and you´ll see what I mean. With FS9´s NG I had enough trouble flying this star, with the NGX it´s a real challenge to say the least!

Yes I see and I now understand, it reminds me the Innsbruck LOWI approach, pretty much a downhill slope over mountains like the one you showed plus an off set of the runway.http://www.vacc-aust...tlist&icao=LOWI - Cheers

Anyway a consideration, if also in the reality it works like that, why in the reality ( at least in my 50 flights I have done as passenger in my life ) it is not so common to apply speed brakes ?When I run 737 NGX pretty much each flight I am forced to apply 4-5 times the speed brakes while in the reality I see it happens only every 2-3 flights instead.

As harsh as it sounds, the girls/guys up front are qualified ATPL/MPL holders with current type ratings to fly the aircraft. We, on the other hand, do not in general possess this vital quality. :)Sorry for the flippant remark. It takes time and planning with the correct forecast information to nail vnav descents without drag required warnings and the like. I know I will need a good few hours more to get on top of this simulation. But hey, that is all the fun of it, isn't it?Andrew