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Desent Path Unachievable

55 posts in this topic

11 minutes ago, 787WannabePilot said:

Thankfully this thread was created, cause I had a lot of trouble descending into Newark (flight on Friday from Seattle).

I had to ride the speedbrake HARD on the way down. 50%, for a good while.  I finally had to go off course for a bit just to reduce my decent rate, thereby slowing the aircraft down.

I was cursing a bit and scratching my head as to why this was so difficult.

Challenges like that are fun.  Good for you that you got it done.

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On 9/1/2017 at 0:36 AM, zmak said:

Aivlasoft is great software that will give you what runway based on your weather program. 

Also gives you suggested sid, stars On a map whilst tracking your aircraft you can easily choose one 

It takes the confusion out. 

Is it compatible with PFRX?

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13 hours ago, 787WannabePilot said:

I finally had to go off course for a bit just to reduce my decent rate, thereby slowing the aircraft down.

You went off course to reduce your descent rate? How does that technique work?

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On 03/09/2017 at 11:53 PM, Spin737 said:

You went off course to reduce your descent rate? How does that technique work?

I think he means he vectored himself off the programed FMC route until he adjusted he decent rate and reached the appropriate altitude, then vector back on FMC route. At least that's how I use to do it when I first started until I got more experienced better at flying it.

I don't think that's in any manual lol

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9 hours ago, branks737 said:

I think he means he vectored himself off the programed FMC route until he adjusted he decent rate and reached the appropriate altitude, then vector back on FMC route. At least that's how I use to do it when I first started until I got more experienced better at flying it.

I don't think that's in any manual lol

This.

Sorry for the delayed response, holiday weekend and all.

And its definitely not in any manual. lol

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On 9/1/2017 at 0:06 AM, Bluestar said:

The NGX comes down just fine, just need to stay on top of energy management.  Some things to consider if having trouble getting the aircraft down are 1) make sure the A/T is disco'd  and the engines are at Flight Idle 2) Use Vert Speed to keep a good rate of descent when decreasing the A/S 3) get the spoilers out early 4) below 10,000 use FLCH. and the most important 5) as soon as it is apparent the aircraft is going to make the upcoming speed/altitude restriction start setting it up for the fix after that. Get ahead of the aircraft.  If all else fails disco the A/P and hand fly it.  

I just tried this approach and didn't have any problems making the speed/crossing restrictions.   

blaustern

Could you explain your second point?

 

I would like to try your method.. I am finding I am coming in way to fast and riding the speed brakes down on the majority of my descents. 

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40 minutes ago, 787WannabePilot said:

coming in way to fast and riding the speed brakes down on the majority of my descents

One of the 737 line pilots that frequently posts here has commented that the real thing needs speedbrakes about half the descents.  I have found that it is normal to use them in the NGX about anytime you don't have a headwind, and you really have to pay attention if the altimeter is high.  The key point is to manage your energy.  I am not a fan of V/S mode, it is much safer to use LVL CH and speedbrakes and get used to speed controlling pitch and drag controlling rate of descent.  You can trade thrust for drag to decrease descent and you have speed protection all the way.

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Are you at idle? What is your planned descent speed? Does it differ from your cruise speed? Do you have winds in the descent page? Are you having problems the whole way down?

Remember - LVL CHG, V/S, and VNAV don't change how the physics works - idle is going to give you the same results in VNAV SPD as it will in LVL CHG and the equivalent V/S. There's no magic mode that gets rid of energy any quicker than another.

High speeds creates more drag, so you can use that to your advantage if you're high and far from the runway. Speed brakes help. Gear helps a lot if needed.

When I'm flying a STAR, I leave it in VNAV and dial the bottom of the STAR. If I need to fix anything, it can be done with SPD INT and SPD BRK, 99% of the time. The most common problem is ATC, not the plane, not the weather. If you can't comply, (RW, of course) you tell ATC and ask for relief or vectors (going off-route).

 

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1 hour ago, downscc said:

One of the 737 line pilots that frequently posts here has commented that the real thing needs speedbrakes about half the descents.  I have found that it is normal to use them in the NGX about anytime you don't have a headwind, and you really have to pay attention if the altimeter is high.  The key point is to manage your energy.  I am not a fan of V/S mode, it is much safer to use LVL CH and speedbrakes and get used to speed controlling pitch and drag controlling rate of descent.  You can trade thrust for drag to decrease descent and you have speed protection all the way.

How normal is it in leave the speed brakes extended (not past the 50% mark) for awhile in descents?

I did try the LVL CH earlier in a flight to NYC, but I found I was hitting the speedbrakes quite often to keep the descent path bubble near the middle.

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4 minutes ago, Spin737 said:

Are you at idle? What is your planned descent speed? Does it differ from your cruise speed? Do you have winds in the descent page? Are you having problems the whole way down?

Remember - LVL CHG, V/S, and VNAV don't change how the physics works - idle is going to give you the same results in VNAV SPD as it will in LVL CHG and the equivalent V/S. There's no magic mode that gets rid of energy any quicker than another.

High speeds creates more drag, so you can use that to your advantage if you're high and far from the runway. Speed brakes help. Gear helps a lot if needed.

When I'm flying a STAR, I leave it in VNAV and dial the bottom of the STAR. If I need to fix anything, it can be done with SPD INT and SPD BRK, 99% of the time. The most common problem is ATC, not the plane, not the weather. If you can't comply, (RW, of course) you tell ATC and ask for relief or vectors (going off-route).

 

1) I am at idle.  Once the plane starts to dip, I put the joystock throttle all the way to 0. I hit F1 once I am under 30k. (I have hit F1 earlier in the past, but my speed drops too quickly causing other problems)

2) .79 is the descent speed, not sure about the cruise speed off the top of my head.

3) I put the winds in the descent page when I reach cruising attitude. I get these winds from the print out from PFRX (w/ active sky).

4) The problem seems to happen once I am under 20k. Sometimes its closer to 10k.  And the problem is I am going to fast, which I either have to ride the speedbrake all the way down, or try not to descent as quick which leads to a domino effect.

 

What do you mean by "Dial the bottom of the STAR" ? 

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25 minutes ago, 787WannabePilot said:

4) The problem seems to happen once I am under 20k. Sometimes its closer to 10k.  And the problem is I am going to fast, which I either have to ride the speedbrake all the way down, or try not to descent as quick which leads to a domino effect.

 

What do you mean by "Dial the bottom of the STAR" ? 

And you're on path, but the speed increases below 20 or 10k? Have you rechecked that you're at idle? What is your N2 and N1?

The bottom is just last lowest altitude for the STAR and transition you're flying. Some operators change the MCP ALT for each step down. I don't. Once I'm given a clearance to "descend via," the bottom altitude is set unless I'm forced to exit VNAV.

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12 minutes ago, Spin737 said:

And you're on path, but the speed increases below 20 or 10k? Have you rechecked that you're at idle? What is your N2 and N1?

The bottom is just last lowest altitude for the STAR and transition you're flying. Some operators change the MCP ALT for each step down. I don't. Once I'm given a clearance to "descend via," the bottom altitude is set unless I'm forced to exit VNAV.

I am on the path till I have to adjust my pitch due to my speed becoming excessive. Then I will hit the speedbrake hard, but sometimes it works.. sometimes it doesn't.

The problems with speed start sometime under 20k. I am generally ok until then.  I hit the F1 key under 30k,  and I don't notice any increase (throttle wise) while descending.   I don't recall my N2 / N1. If this is something I am going to have to re create and take notes I will.

Frankly, because I don't use the ATC I just dial by MCP ALT to 1000 and just cruise on down. By the time I reach that altitude I am already on approach and it doesn't matter.

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5 minutes ago, 787WannabePilot said:

I am on the path till I have to adjust my pitch due to my speed becoming excessive. Then I will hit the speedbrake hard, but sometimes it works.. sometimes it doesn't.

Not much information to go one here... but I would guess your target descent speed is less than 280?  Try using 280 or higher.  Also don't ignore FMS when it calls for drag at the 10 kt above target speed,  the more excess speed you carry the harder it is to shed it later. Are you using only keyboard or do you have a throttle controller?  Like I've said before, using speedbrakes is normal about half the time and you don't want to wait to react to variance.  Sometimes I've got things working such that about a quarter speedbrake freezes the speed until I get down into thicker air where less additional drag is required.

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Just now, downscc said:

Not much information to go one here... but I would guess your target descent speed is less than 280?  Try using 280 or higher.  Also don't ignore FMS when it calls for drag at the 10 kt above target speed,  the more excess speed you carry the harder it is to shed it later. Are you using only keyboard or do you have a throttle controller?  Like I've said before, using speedbrakes is normal about half the time and you don't want to wait to react to variance.  Sometimes I've got things working such that about a quarter speedbrake freezes the speed until I get down into thicker air where less additional drag is required.

Decent speed is at 279 or .79.  How high should I go?

Joystick w/throttle and keyboard.  Is it 'normal' to extend them for minutes at a time? I am guessing yes in this case.

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42 minutes ago, 787WannabePilot said:

Decent speed is at 279 or .79.  How high should I go?

Joystick w/throttle and keyboard.  Is it 'normal' to extend them for minutes at a time? I am guessing yes in this case.

It is indeed normal to deploy speedbrakes for minutes at a time.  Set the option ON to always show your throttle position, and in your descent give your throttle and little nudge up and down watching the N1 gauges.  You'll be able to tell if the aircraft throttle is close by comparing it to the blue indication of your controller position.  The only NGX I've noticed not always keeping to idle is the B736 but haven't really figured out why that happens.  279 is okay but usually there is a 280 constraint somewhere so I select that to avoid the annoying "unable 280 at" messages.  I usually use 280, although sometimes I will hear Houston using 310.  Just depends on location and controller.

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