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skwaL

Speed constraints issue.

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When I am on descent below 10000 flying -8, aircraft does not follow speed constraints, it just want to slow down to final approach speed. This was not the case with -400.

Any ideas what I could be doing wrong?

 

Thanks.

Konstantin

Edited by skwaL

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Correction to this. Airplane still want to go to approach speed below 10000ft the second I start using flaps. Does not follow constraints

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On 9/30/2018 at 12:12 AM, skwaL said:

This was not the case with -400.

This is correct. They're different aircraft, and behave differently. Use SPD INTV if you need to.

There's a reason there are still people up front. 😉

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18 hours ago, skwaL said:

Does not follow constraints

In addition to what Kyle suggests, be aware that the FMS treats speed constraints as AT OR BELOW so it is correct if it say for example slows to 210 rather than stay at 240 if there is a 210 constraint ahead and it will not be able to decelerate from 240... or even if it goes to 190 for similar reason.  Let the airplane show you how it works, unless you have ATC asking you to keep the speed up until 4 nm final then use SPD INTV.

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On 10/6/2018 at 12:31 PM, downscc said:

In addition to what Kyle suggests, be aware that the FMS treats speed constraints as AT OR BELOW so it is correct if it say for example slows to 210 rather than stay at 240 if there is a 210 constraint ahead and it will not be able to decelerate from 240... or even if it goes to 190 for similar reason.  Let the airplane show you how it works, unless you have ATC asking you to keep the speed up until 4 nm final then use SPD INTV.

Yea but what happens lets say I have 40 miles to airport, every 10 miles it got from 240/7000 220/5000 200/4000 170/2000..... As Soon As I pass 10000ft it will want to decel to 170 the second I start lowering flaps. It will ignore other constraints no matter how far I'm from the airport. Doesn't seem right. 

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2 hours ago, skwaL said:

Doesn't seem right.

Why not.... if the aircraft is descending it cannot slow down.  It must either slow down or go down. 

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23 minutes ago, downscc said:

Why not.... if the aircraft is descending it cannot slow down.  It must either slow down or go down. 

So why have speed constraints then if you just plan on slowing down to approach speeds after 10k 😛

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Posted (edited)

Speed constraints are AT OR BELOW.  Depending on the arrival, there is often plenty of distance available to decrease descent rate to allow slowing.  This is what she does at the 240/10000 and given a chance she will do it for 190 but there has to be room for the deceleration ramp.

Edited by downscc

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Posted (edited)
3 hours ago, skwaL said:

Yea but what happens lets say I have 40 miles to airport, every 10 miles it got from 240/7000 220/5000 200/4000 170/2000..... As Soon As I pass 10000ft it will want to decel to 170 the second I start lowering flaps. It will ignore other constraints no matter how far I'm from the airport. Doesn't seem right. 

I use FLCH when descending below 10,000.  This assures me that the autopilot will be using the airspeed and altitude restraints that I want it to use.  One thing I also do is draw a 3 mile arc around the final approach fix.  This 3 mile arc is a reminder to make sure that I have the Gear/Flaps/Slats/ Cleared to land, if not I must execute a go around. 

I know, I'm old and ol' school.  ROFL

Edited by Bluestar

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15 hours ago, Bluestar said:

I use FLCH when descending below 10,000.  This assures me that the autopilot will be using the airspeed and altitude restraints that I want it to use.  One thing I also do is draw a 3 mile arc around the final approach fix.  This 3 mile arc is a reminder to make sure that I have the Gear/Flaps/Slats/ Cleared to land, if not I must execute a go around. 

I know, I'm old and ol' school.  ROFL

I did something similar arriving KHSV Huntsville the other day, a GTI PANC KHSV mission.  Huntsville has no arrivals and the ground track for the actual flight indicated a vector to get off the airway before descending.  I used off path descent page and FLCH with thrust for the entire descent from FL370 to the IAF for the RNV approach.  It's kinda fun to get off the routine of flying the magenta like.

I use a 5 nm arc when I'm self vectoring a downwind (radar downwind is 5 nm from airport), and in the past I've used a bearing/distance at the IF or FAF to gauge the final intercept course but last year or so I've gotten lazy and just eyeball it.

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