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DH747

Drag Required

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Good morning,

 

don't know if it's a bug, but during the descent to Hamburg I often got the FMC msg 'Drag Required', although the engines were running above idle (around 50-60% N1). The AP and VNAV/LNAV were activated. Maybe it was caused by turbulences?

 

Best regards

Daniel Harms

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Sometimes the aircraft is maintaining its speed but got to descent more to follow the glide path. So its asking for more drag to help to maintain the speed and descent at a greater fps 

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If you aren't using wind data, the fmc has no way of prediting a proper descent path, so it will often find itself going too fast to reach a constraint. This message is telling you to add drag like flaps or spoiler to help slow it down.

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In other word apply spoiler and when the spoiler is no longer needed FMC msg will just disappear and then retract the spolier.

Just do what you are told !  :ph34r:  :P

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Thanks yours, but I'm actually wondering to get this msg although the engines are running at 50% N1. From my logical point of view, first the engines should go to idle and if that's not sufficient, then asking for more drag

 

Best regards

Daniel Harms

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Thanks yours, but I'm actually wondering to get this msg although the engines are running at 50% N1. From my logical point of view, first the engines should go to idle and if that's not sufficient, then asking for more drag

 

Best regards

Daniel Harms

Yes that is correct.

 

make sure AT is engaged.

make sure you have setup your thrust leavers in the CDU/setup menu correctly (otherwise it could be that your throttle quadrant (if you are using one) is overriding what the AT wants.

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Thanks yours, but I'm actually wondering to get this msg although the engines are running at 50% N1. From my logical point of view, first the engines should go to idle and if that's not sufficient, then asking for more drag

 

Best regards

Daniel Harms

 

See that high n1 rate IS idle... at high speeds the fans will spin on their own. So that is the lowest number possible at that speed and altitude.

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More then Likely THR HOLD is active hence why your throttle is commanding 50% As Rob pointed out check your actual throttle position.

See that high n1 rate IS idle... at high speeds the fans will spin on their own. So that is the lowest number possible at that speed and altitude.

No

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Read your FMAs.... aloud to yourself.... You might get some strange looks from your trolley dolly, but you will know what AFDS is doing. Also, do calibrate your throttles (and all your axis' for that matter). TAKE YOUR TIME- most people do that way to fast. Set appropriate end points so you have null zones. Set your preference of A/T interaction in the CDU PMDG/OPTIONS menu.

 

All that done- AFDS and VNAV still require the chap betwixt the glareshield and the headrest to FLY. We (simmers) have gotten all to used to unrealistic simulations that follow the magenta line and VFP like Dorothy on the yellow brick road. The NGX taught simmers this was not so in IRL. The 777 continues our education. Boeing decided long ago that all the automatics would NEVER replace the pilot- I agree.

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I also got this message while I was descending to land... so whenever you see this message appear, all you need to do is extend your spoilers? Is that the same as extending the flaps?

 

I notice as I am getting close to the approach that my speed is about 230kts, but on the FMC is shows like 170. I have AT actived so why isn't the FMC automatically taking it down to that speed? 

 

I am using ASN for wind data, thats being loaded into the FMC, and also des wind data as well.

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I also got this message while I was descending to land... so whenever you see this message appear, all you need to do is extend your spoilers? Is that the same as extending the flaps?

 

I notice as I am getting close to the approach that my speed is about 230kts, but on the FMC is shows like 170. I have AT actived so why isn't the FMC automatically taking it down to that speed? 

 

I am using ASN for wind data, thats being loaded into the FMC, and also des wind data as well.

 

Do some reading up on the difference between VNAV PATH and VNAV SPEED.

 

Spoilers are not the same as flaps, if you need to reduce speed use spoilers. If you need to reduce speed and expect to maintain a speed below "flaps up speed", then extend the appropriate flaps too.

 

There is a thing called physics at work here. If your decent PATH is such that even at idle power your aircraft will not slow down to your required/expected speed, there is nothing the A/P or VNAV or FMC can do (indeed VNAV may disconnect as UNABLE). It is your job as pilot to take the necessary steps to achieve correct speed.

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I have had this issue when my hardware thrust levers were left above idle, and I did not have my PMDG thrust lever override set correctly. The power might only roll back to 50% or so based on the hardware lever setting. Double check your power lever(s) are right back to idle on descent.

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I also got this message while I was descending to land... so whenever you see this message appear, all you need to do is extend your spoilers? Is that the same as extending the flaps?

 

I notice as I am getting close to the approach that my speed is about 230kts, but on the FMC is shows like 170. I have AT actived so why isn't the FMC automatically taking it down to that speed? 

 

 

You need to do Tutorial 1. Speed Control for the T7 is explained in that document.

 

If you don't know the difference between flaps and spoilers, you might want to search the Internet for documents pertaining to basic airmanship.

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One of the differences is that spoilers kill lift while flaps increase it.

Spoilers distrupt the high speed - low pressure airflow over the top of the wing. During descent, it helps to achieve steeper descents for the same airspeeds or slower speeds for the same descent rate. On rollout, it helps the aircraft to stay on the runway by killing lift on the wings and it also helps to increase the efficiency of the wheelbrakes (less lift yields more weight on the mains resulting higher friction between the wheels and the runway).

 

Or at least that's how I know.. :)

 

Cheers,

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One of the differences is that spoilers kill lift while flaps increase it.

Spoilers distrupt the high speed - low pressure airflow over the top of the wing. During descent, it helps to achieve steeper descents for the same airspeeds or slower speeds for the same descent rate. On rollout, it helps the aircraft to stay on the runway by killing lift on the wings and it also helps to increase the efficiency of the wheelbrakes (less lift yields more weight on the mains resulting higher friction between the wheels and the runway).

 

Or at least that's how I know.. :)

 

Cheers,

 

You are only partially correct, any device that increases lift, will also increase drag to an extent, and certainly flap settings of more then 20 are adding quite a bit of drag than lift at that point. (give or take).

 

Spoilers, are pretty much as you have described them. They also benefit from not usually having a maximum extension speed limit, and can be used right the way from TOD if need be. Unlike Flaps. (or gear)

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