Boeing Airspeed Bugs Bug me too (love the pun geddit)

[Tee Emm]

Various B737 Series FCTM recommend that two white bugs be set together on the ASI to indicate Vref. When these white moveable markers are squeezed together they seem to cover several knots rather than as desired a specific airspeed. Exactly what is the advantage of setting two white bugs at Vref instead of one? Is it because a spare bug should be placed somewhere rather than be shoved up well out of the way?

Why not have one white bug set on Vref just like other white moveable bugs are set at V1, VR, V2+15 and clean maneuver speed (210, 220 or 230 knots)

[SNS3Guppy]

Are you talking takeoff or landing...V2, or Vref?

When we land, we use a bug speed which is not Vref. We don't bug Vref. We land flaps 25 rather than flaps 30, due to Stage III noise restrictions (747...not 737, but still boeing). We base all our other airspeed bugs of the bottom bug. With the bottom bug set at Vref+5, we then have bugs set at bug+20, bug+40, bug+60, and bug+80...and we maintain 10 knots above those speeds until established on final. (We have a 15 degree bank limitation on speed, but can bank up to 30 degrees with the 10 knot increase).

I'm familiar with the double bug recommendation...but it doesn't make anything less accurate. If you really want to split a knot and fly that precisely, then use one of the little white pointers or the other, or fly the space between them, for that matter. Considering the airspeed indicator may have an error up to 4-6 knots, depending, then it's really not compromising the ability to fly a safe, and accurate approach by double-bugging.

[BoeingBoy]

As a young lad on the 737-200 more years ago than I will admit to here it was told to me that setting the lower of the double bugs on Vref40 meant that the top of the second bug gave you a visual guide to where Vref40+5 was and therefore you had a visual guide to your minimum speed until approaching the flare.

Well, at that age I also believed in Santa!

[BelArgUSA]

Tee Emm - I second SNS3Guppy's "bug" position as standard in Boeing FCTMs.
Or at least, for the Boeing aeroplanes of my generation.
A "double white bug" is, in the 747 (and 737 - or even 727) set on Vref.
As to flying within 1 knot of speed - you are much more proficient than me.
On a good day, I was able to achieve +/- 2 (?) knots accuracy when hand flying.
That is, if I was not too tired.
Maybe you are using Lufty standards - one/half of a knot...?
I suspect that BA is certainly of equal standards to LH's...
:D
Happy contrails

[BOAC]

TM - stick with BB's simple answer! Good advice. If you are concerned about the 'width' of the Vref double bug, you would be the first pilot I have seen to get near to Vref other than on the landing roll:) so have no fear. I think the simple idea is to 'highlight' your min speed at BB says.

[Tee Emm]

As to flying within 1 knot of speed - you are much more proficient than me.

I didn't mean to infer I could fly to within one knot - far from it. No, my query was a simple one and that was did anyone know why Boeing opted to set two white moveable indices (bugs in my language) at Vref on the round dial ASI. On looking back I can only think it may have been because there was a spare bug and nowhere to put it for landing. Let's face it it was a trivial query anyway and probably not worth even worrying about. But thanks for the replies, though.