FMC Takeoff Ref Page

[ark 1,288]

What is the significance of the QRH ON/OFF option at LSK 6R on the FMC Takeoff Ref page? I also notice when QRH is ON, there sometimes is a slight difference (1 or 2 knots) between one or more of the listed V speeds (eg, v1=119 vs V1=120) -- I ignore the slight difference. If I shouldn't ignore it, what should I do about it?

Thanks,

Al

[Cristi_Neagu 134]

QRH means the FMC calculates your v speeds based on the QRH (quick reference handbook). With it off, you have to manually enter them.

 

Also, you might want to look up what v speeds actually are...

[ark 1,288]

QRH means the FMC calculates your v speeds based on the QRH (quick reference handbook). With it off, you have to manually enter them.

 

Also, you might want to look up what v speeds actually are...

Thanks for the input.

I know very well what the v speeds are. Just wanted to understand how the difference comes about on that page. If one set is based on the QRH, how did the FMC come up with the other set?

Al

[pcubine 143]

What is the significance of the QRH ON/OFF option at LSK 6R on the FMC Takeoff Ref page?

 

 

See page 11.40.49 in the PMDG NGX FCOMv2.

[ark 1,288]

See page 11.40.49 in the PMDG NGX FCOMv2.

Thanks.

Al

[77west 139]

Thanks for the input.

I know very well what the v speeds are. Just wanted to understand how the difference comes about on that page. If one set is based on the QRH, how did the FMC come up with the other set?

Al

As Kyle will say, aviation is not as rigid as one would think. I believe a small 1 or 2 kt difference is probably due to rounding or conversions. It will not impact your takeoff, as by the time the wheels leave the ground you are past V1 and Vr anyhow. Now if it was a 4kt or higher difference, I would look into it further.

[scandinavian13 5,192]

 

 

As Kyle will say, aviation is not as rigid as one would think.

 

Thanks for the mention, and you're definitely right.  The cool thing about aviation is that we can get so finely detailed.  The problem with aviation is that there is just enough variability that concentrating on details that are too fine becomes counterproductive.

 

At the same time, related to this thread topic, I'm not entirely sure I understand the issue.  When you turn the QRH option off, the speeds should disappear.  When you turn it on, the computed speeds should reappear.  There isn't a "second set" of numbers at all from my experience, or even in the FCOM.  Sounds almost like the the OP entered speeds from TOPCAT, or some other tool and is then comparing them to the QRH speeds.  The speeds entered on the actual LSK spots are either calculated, or "downselected" from the QRH calc speeds.  Again, the FMC doesn't have two sets of data here.  If the speeds don't match the QRH speeds (the smaller numbers followed by a > symbol), then they must have been entered by hand, based on some other calculation.  If this is the case, and they're slightly off (V1 is expected, since the FMC only calculated balanced field V1, while TOPCAT calcs runway-specific V1), refer to Wes' post above.

 

In other words, the very first time you show up on the TAKEOFF REF page, you should either see absolutely nothing (QRH OFF) or speeds to the left of blanks (---, which is the QRH ON option).  OP: Is this not what you're seeing?

[ark 1,288]

 

At the same time, related to this thread topic, I'm not entirely sure I understand the issue.  When you turn the QRH option off, the speeds should disappear.  When you turn it on, the computed speeds should reappear.  There isn't a "second set" of numbers at all from my experience, or even in the FCOM.

 

 

On FCOM v2 pg 11.40.48 you will see a representation of the FMC Takeoff Ref pg with two columns of V speeds that differ slightly (by 1 Kt). This is exactly the situation I've run into, but don't know why.  In this situation pushing the LSKs does not transfer the QRH values into the right hand column. I’m not concerned about the 1Kt difference between a given v speed, just curious how this comes about and why pushing the respective LSK does not update the value.

Thx,

Al

 Edit: Looks like the two columns of V speeds may be related to Change of Performance Data After V Speed Entry,  see pgs  11.40.49 and 11.40.50. It is not clear to me which column of speeds is the "latest", although I would guess the right column since I can't find a way to "load" the left column using the LSKs.