GeographyFlyer
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Descent in a holding pattern - Boeing 777

Sat Apr 20, 2019 12:37 pm

Hey guys,

What mode (FLCH,VNAV,V/S) do you use when you are given a clearance to descent in a holding pattern? Or do you program it into the FMC? (B777)

Thank you very much in advance, GeographyFlyer.
 
FlyHossD
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Re: Descent in a holding pattern - Boeing 777

Sat Apr 20, 2019 3:47 pm

Quite often, descents in a holding pattern are given 1,000' feet at a time. So depending on workload, I'd either use VNAV (low workload) or Vertical Speed (high workload).
My statements do not represent my former employer or my current employer and are my opinions only.
 
26point2
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Re: Descent in a holding pattern - Boeing 777

Sat Apr 20, 2019 4:10 pm

VS. Likely there’s another dude 1000’ below you also in holding. Modulating VS to a reasonably low descent rate will ensure no TAs or RAs.
 
DGVT
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Re: Descent in a holding pattern - Boeing 777

Sat Apr 20, 2019 9:04 pm

FlyHossD wrote:
Quite often, descents in a holding pattern are given 1,000' feet at a time. So depending on workload, I'd either use VNAV (low workload) or Vertical Speed (high workload).


Can you elaborate why VNAV is used when you have low workload? I would have thought VNAV is more straightforward than VS...
 
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Starlionblue
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Re: Descent in a holding pattern - Boeing 777

Sun Apr 21, 2019 12:42 am

DGVT wrote:
FlyHossD wrote:
Quite often, descents in a holding pattern are given 1,000' feet at a time. So depending on workload, I'd either use VNAV (low workload) or Vertical Speed (high workload).


Can you elaborate why VNAV is used when you have low workload? I would have thought VNAV is more straightforward than VS...


I think he meant that VNAV is lower workload than VS.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
mmo
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Re: Descent in a holding pattern - Boeing 777

Sun Apr 21, 2019 11:08 am

Personally, I use V/S and about 300 FPM descent. That provides a nice pitch change, a descent rate which won't trigger an RA if there is traffic below and best of all, the thrust reduction won't be so much the HP bleeds open.
If we weren't all crazy we'd all go insane!
 
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zeke
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Re: Descent in a holding pattern - Boeing 777

Sun Apr 21, 2019 1:29 pm

mmo wrote:
Personally, I use V/S and about 300 FPM descent. That provides a nice pitch change, a descent rate which won't trigger an RA if there is traffic below and best of all, the thrust reduction won't be so much the HP bleeds open.


Except the standard rate ATC expects in a hold is 1000 fpm. V/S is the only way to do it safely.

The reason the want 1000 fpm is so everything is predictable when your stacked.

You have one aircraft doing 300 fpm and another a higher rate, you can end up having wake problems. Not something I enjoy when sitting in a hold below 4 A380s trying to get into DXB.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
mmo
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Re: Descent in a holding pattern - Boeing 777

Sun Apr 21, 2019 4:38 pm

In theory, you are correct. However, if you turn the thumbwheel to -1000' it begins to descent and almost goes to capture the selected altitude.

Zeke, you might want to read a few documents, for example, the UK AIP FOR London is 500 FPM while the FAA expects 500-1500 fpm descent rate. One size does not fit all.
If we weren't all crazy we'd all go insane!
 
FlyHossD
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Re: Descent in a holding pattern - Boeing 777

Sun Apr 21, 2019 5:22 pm

Starlionblue wrote:
DGVT wrote:
FlyHossD wrote:
Quite often, descents in a holding pattern are given 1,000' feet at a time. So depending on workload, I'd either use VNAV (low workload) or Vertical Speed (high workload).


Can you elaborate why VNAV is used when you have low workload? I would have thought VNAV is more straightforward than VS...


I think he meant that VNAV is lower workload than VS.


No. I meant I would use VNAV when otherwise the workload was low and VS if the other workload was high. Why? To my way of thinking, setting the new altitude in the MCP and then setting the new altitude in the FMC requires more keystrokes than setting the new altitude in the MCP, then selecting VS and rolling in the desired rate of descent (generally 1,000 fpm). That is, I could do the second method more quickly.
My statements do not represent my former employer or my current employer and are my opinions only.
 
Redbellyguppy
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Re: Descent in a holding pattern - Boeing 777

Sun Apr 21, 2019 6:47 pm

Why would I use vnav in my 737? Because why not. Set the altitude and press altitude intervene. Box figures out LRC or holding speed for new altitude, everything is cues up for further descent later. There are many ways to skin the cat, but, the folks who designed an integrated cockpit presume you will utilize the integration.
 
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Starlionblue
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Re: Descent in a holding pattern - Boeing 777

Sun Apr 21, 2019 9:41 pm

FlyHossD wrote:
Starlionblue wrote:
DGVT wrote:

Can you elaborate why VNAV is used when you have low workload? I would have thought VNAV is more straightforward than VS...


I think he meant that VNAV is lower workload than VS.


No. I meant I would use VNAV when otherwise the workload was low and VS if the other workload was high. Why? To my way of thinking, setting the new altitude in the MCP and then setting the new altitude in the FMC requires more keystrokes than setting the new altitude in the MCP, then selecting VS and rolling in the desired rate of descent (generally 1,000 fpm). That is, I could do the second method more quickly.


Understood.

I was thinking Airbus. We don't need to set the new altitude in the FM. It will be set automagically, so you could just set the altitude in the FCU (MCP) and push for a managed (VNAV) descent. One less twist compared to VS.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Tartarus
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Re: Descent in a holding pattern - Boeing 777

Mon Apr 22, 2019 5:13 pm

It's our 777 SOP to only use Basic Modes (FLCH or V/S) while in the hold.
This was due to a few incidents where upon engaging VNAV, the aircraft actually pitched up due to the TGT ALT in the VNAV descent page.
 
Tartarus
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Re: Descent in a holding pattern - Boeing 777

Mon Apr 22, 2019 5:16 pm

mmo wrote:
In theory, you are correct. However, if you turn the thumbwheel to -1000' it begins to descent and almost goes to capture the selected altitude.

I've spent longer in holds than I'd ever have liked too, and I've never seen a 1000fpm descent rate capture quickly. The logic will give an ALT capture at about 150 feet to go with that kind of rate.
 
mmo
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Re: Descent in a holding pattern - Boeing 777

Mon Apr 22, 2019 8:45 pm

Tartarus wrote:
mmo wrote:
In theory, you are correct. However, if you turn the thumbwheel to -1000' it begins to descent and almost goes to capture the selected altitude.

I've spent longer in holds than I'd ever have liked too, and I've never seen a 1000fpm descent rate capture quickly. The logic will give an ALT capture at about 150 feet to go with that kind of rate.


I would assume you are in a slower aircraft. I held at higher altitudes with a .8 IMN holding speed (assigned) and I assure you, it would have happened. I suppose we could talk technique vs. procedure but as the saying goes, 'everyone has one and they all stink'.
If we weren't all crazy we'd all go insane!
 
BoeingGuy
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Re: Descent in a holding pattern - Boeing 777

Mon Apr 22, 2019 11:40 pm

26point2 wrote:
VS. Likely there’s another dude 1000’ below you also in holding. Modulating VS to a reasonably low descent rate will ensure no TAs or RAs.


In your scenario, FLCH will give you about a 500 fpm descent rate on average. FLCH tries to do the climb or descent in 2 minutes, if able.

I'm assuming in the various pilot responses here about using V/S vs VNAV, your roll mode will be LNAV.

I didn't think that V/S was used much in actual service; I expected that FLCH is almost always used if you aren't in VNAV since it provides stall or overspeed protection and V/S does not. The only procedures I'm aware of that call for it are engine failure at takeoff or in heavy turbulance (because FLCH is a speed-through-elevators mode and airspeed will be jumping around).

I'm being educated that my understanding was not correct. Apparently you guys do use V/S a lot more than I thought.
 
BoeingGuy
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Re: Descent in a holding pattern - Boeing 777

Mon Apr 22, 2019 11:44 pm

Tartarus wrote:
mmo wrote:
In theory, you are correct. However, if you turn the thumbwheel to -1000' it begins to descent and almost goes to capture the selected altitude.

I've spent longer in holds than I'd ever have liked too, and I've never seen a 1000fpm descent rate capture quickly. The logic will give an ALT capture at about 150 feet to go with that kind of rate.


There is specific control logic as to when ALT captures. It's based on closer rate and a few other things. You're correct. At a 1000 fpm descent rate, ALT certainly won't capture if you are 1000 feet away from your MCP target. 150 feet sounds about in the ballpark.
 
FlyHossD
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Re: Descent in a holding pattern - Boeing 777

Tue Apr 23, 2019 12:23 am

BoeingGuy wrote:
...I didn't think that V/S was used much in actual service; I expected that FLCH is almost always used if you aren't in VNAV since it provides stall or overspeed protection and V/S does not...

...I'm being educated that my understanding was not correct. Apparently you guys do use V/S a lot more than I thought.


You've made a very good point about stall protection. However, in my view, that's not much of a concern in a descent. And I can't remember ever climbing in a holding pattern - in that case, I would have likely used either VNAV or FLCH depending on the situation.
My statements do not represent my former employer or my current employer and are my opinions only.
 
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Starlionblue
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Re: Descent in a holding pattern - Boeing 777

Tue Apr 23, 2019 1:47 am

As FlyHossD says, low speed protection is not that big a concern in a descent. On the 'bus, VS is used frequently in the descent, for example to reach an altitude at a waypoint, but rarely in the climb, especially at high altitude where margins are slim.

VS can be used to "neatly" intercept the glideslope. No point descending far below the GS before intercepting. Neater to use a low VS to give a constant descent instead of descending, leveling off, capturing the GS and then descending again.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
FlyHossD
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Re: Descent in a holding pattern - Boeing 777

Wed Apr 24, 2019 10:53 pm

Starlionblue wrote:
VS can be used to "neatly" intercept the glideslope. No point descending far below the GS before intercepting. Neater to use a low VS to give a constant descent instead of descending, leveling off, capturing the GS and then descending again.


Thumbs up. To me that's a mark of a craftsman; an aviator rather than a systems or flight manager. In intercepting an ILS glideslope, I'd often use 400-500 feet per minute to join a glideslope (often around 800-900 fpm once established on the GS). That is, I tried to fly "softly" - like my grandmother was onboard every flight. She was terribly afraid of flying.
My statements do not represent my former employer or my current employer and are my opinions only.

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