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vegasjon

Landing VRef speed calculation

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How do you all calculate the Landing Vref speed for your FMS? i imagine there is a chart that takes into consideration current weight, airport info ,etc?


Jon Richardson

Henderson, NV

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Hi,

 

the fmc calculates everything for you. You simply have to insert it. To do so just open the "APPROACH REF"-Page in your FMC by clicking the init-button when in cruise or by going to the "Index"-page by pressing LSK6-Left and then again LSK6-Left to go to the "APPROACH REF"-Page. There you select the desired speed in the scratchpad by clicking the LSK to the right of the speed and flap-setting you want and insert it in your fmc by pressing LSK4-Right to "FLAP/SPEED". 

 

I am currently talking about the 777 but in the other Boeing models it is basicially the same.

 

Hope I helped.


Dennis Grümer

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As noted by Dennis, the only thing you really need to do is input the correct data into the FMC, but the one thing you have to do manually (since you have a choice in the matter) is determine what flap setting you want. It will be the wind speed (and specifically if it is gusting or there is a notable wind gradient on the approach) which will determine the wisest choice for that. A quick tune in to the ATIS, or a look at an EFB or weather program which can determine the winds at your destination will be in order.

As I'm sure you know, you'll want less flaps for approaches when there is a chance of gusting or variable winds, since large flap settings will have you flying slower and will also mean your aeroplane cannot accelerate as quickly should the oncoming wind speed suddenly drop, so it's better to err on the side of caution and go for a higher landing speed with less flaps in those circumstances, that is unless there is significant runway contamination with water or slush or whatever, in which case a high landing speed might not be a great idea if the runway is not an especially long one and then the decision will require a bit more careful consideration of the relative pros and cons of approach speed versus stopping distance.


Alan Bradbury

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The FMC APPROACH REF page shows the current calculated gross weight. If you use that figure, by the time you actually touchdown the weight will be less and Vref might be a knot or two less as a result. I'm not a real world pilot but from what I've read some pilots calculate the estimated gross weight at touchdown and enter that figure in the APPROACH REF page, overriding the FMC calculated value.

Not that I do this in PMDG's sims myself, my flying isn't accurate enough to make it worthwhile, but if you want to be very precise then it's something to consider.

Edited by kevinh

ki9cAAb.jpg

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After entering STAR and approach in FMC check the progress page to see what is the estimate fuel at destination.

Check current on board. Subtract fuel you have with the fuel estimated and you are going to have the fuel you are going to burn.

Co to the Approach Ref page and subtract the value there with the fuel value you found above. This will be your landing weight. Put this in the 1L and you will have the correct speeds.

 

 


Chris Makris

PLEASE NOTE PMDG HAS DEPARTED AVSIM

You can find us at http://forum.pmdg.com

 

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What about adjusting for the wind variable (i.e vref + (half the steady wind) + (difference between steady and gust))? 


Matt King

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8 hours ago, Olympic260 said:

After entering STAR and approach in FMC check the progress page to see what is the estimate fuel at destination.

Check current on board. Subtract fuel you have with the fuel estimated and you are going to have the fuel you are going to burn.

Co to the Approach Ref page and subtract the value there with the fuel value you found above. This will be your landing weight. Put this in the 1L and you will have the correct speeds.

 

 

Dispatched ZFW + estimated fuel at destination  = estimated landing weight.


Mauricio Brentano

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13 hours ago, kingm56 said:

What about adjusting for the wind variable (i.e vref + (half the steady wind) + (difference between steady and gust))? 

What about it?  What you end up with is Vref+5+wind additive.  The FMC defaults to "+5" and its up to pilot to increase the "+5" as desired.  See also for the NGX FCTM 1.18 and note that you should not make adjustments that exceed Vref+20 or landing flap placard speed minus 5 kts, whichever is lower.  The point is the FMC doesn't determine wind additive but allows it.


Dan Downs KCRP

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2 hours ago, downscc said:

What about it?  What you end up with is Vref+5+wind additive.  The FMC defaults to "+5" and its up to pilot to increase the "+5" as desired.  See also for the NGX FCTM 1.18 and note that you should not make adjustments that exceed Vref+20 or landing flap placard speed minus 5 kts, whichever is lower.  The point is the FMC doesn't determine wind additive but allows it.

 I was responding to the OP's question; while he was given great answers, they failed to account for the wind variable.  The goal was to make him cognizant of said factors, specifically how they relate to VREF calculations. 


Matt King

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On 9/3/2018 at 4:18 PM, vegasjon said:

How do you all calculate the Landing Vref speed for your FMS? i imagine there is a chart that takes into consideration current weight, airport info ,etc?

For all practical purposes and assuming you are 'airborne' at the time and approaching the TOD, simply check your aircraft's current gross weight in the FMC and deduct the FMC's predicted fuel burn to destination from that figure (you can work it out using PROGRESS Page 1).  Then insert this lower gross weight over the current APPROACH REF computed Gross Weight and you will see the calculated VRef speeds for Flaps 25 and 30 for your estimated Landing Weight.  Unless you end up in the Hold for a long time these VRef speeds will be accurate enough for most approaches and pilots - provided you are not among the very fortunate few who say they can fly accurately to 1 knot!

If we take the PMDG B744 as an example, the wind speed does not in itself determine the amount of Landing Flap to use because Flaps 25 is the preferred selection for the vast majority of normal landings on either four or three operating engines.  However, the wind speed (especially if it is a tailwind) together with the approach speed, airfield pressure altitude and ISA Temp, Runway landing distance and condition will all need to be considered when deciding on the correct Autobrake setting to use.

You should always aim to extend any Flap setting using the current minimum manouevering speed + 10kts as a guide, because this will help to reduce the stress loads on the Flap structures and increase their overall airframe life.  Using Flaps 25 is especially important at the higher landing weights because the aerodynamic loads are higher and there is also a greater risk of experiencing a Flap Load Relief if Flaps 30 is used. The main exceptions to the use of Flaps 25 when Flaps 30 should be used are low viz autolands, high altitude airfields, contaminated or limiting runways and certain abnormal landings.

Boeing actually recommend an approach speed wind correction of 1/2 the headwind plus all of the gust up to a maximum wind correction of +20 kts.  In all cases the gust correction should be maintained to touchdown whilst the steady wind correction should be bled off as the the aircraft approaches the touchdown zone.  If the wind is calm and no wind shear exists, or is light and variable then the recommended approach speed is VRef + 5 kts, with the 5kts again being bled off as the aircraft approaches the touchdown. In the case of a tailwind the approach speed should be VRef.    

 


Bertie Goddard

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On 9/3/2018 at 1:34 PM, kevinh said:

The FMC APPROACH REF page shows the current calculated gross weight. If you use that figure, by the time you actually touchdown the weight will be less and Vref might be a knot or two less as a result. I'm not a real world pilot but from what I've read some pilots calculate the estimated gross weight at touchdown and enter that figure in the APPROACH REF page, overriding the FMC calculated value.

Not that I do this in PMDG's sims myself, my flying isn't accurate enough to make it worthwhile, but if you want to be very precise then it's something to consider.

You’re correct, we do calculate the landing weight and enter the weight/speed we will assume to be at touchdown. When I brief, it’s usually 30-45 minutes before landing or roughly 10 minutes to T/D and the speed will have changed by the time we land. A very down and dirty calculation in the 767 is a 1 knot reduction for every 5000 lbs of fuel burned. Another thing that’s nice to know is how much extra runway you’ll use per extra knot of airspeed. In the 767, it’s a little over 200 feet per knot. If you cross the threshold 5 knots fast, that’s an increase of over 1000 feet assuming you don’t slam on the brakes to stop in a shorter distance. Certainly something to think about.


Sean Wood

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