RODOL
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Why 126 Kts Selected?

Fri Jul 15, 2005 8:03 pm


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You will note that 126 kts has been selected in the speed window on this Kittyhawk 737. My question is, presuming this to be either v1 or vr why has this speed been selected, I thought the pilot rotated the aircraft by visual reference to the speed bugs etc, and engaged AT for climbout, say 230 kts. Or is this something to do with the TOGA settings. Pardon my ignorance.
 
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Jetlagged
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RE: Why 126 Kts Selected?

Fri Jul 15, 2005 9:54 pm

For takeoff, the speed window would be set to V2 or V2+10, depending on airline SOP. V1 and Vr would be set using the smaller white bugs, manually positioned around the ASI bezel. In the photo they are at about 112 and 114, which makes sense relative to the speed bug. They may be set around one speed (113) as V1 and Vr could be the same value. The other white bugs are set to flap retraction speeds (about 143 and 243).

The speed bug (salmon bug) slaved to the speed window selection is clearly visible in the F/O's ASI, but not so visible in the Captain's due to the angle of view.

The speed window selects the required airspeed for the AFCS. During climb, the ATS is controlling engine N1, not airspeed, which is controlled by aircraft pitch angle. In level flight the ATS controls airspeed. In VNAV the FMC commands airspeed, but the crew can intervene.
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XFSUgimpLB41X
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RE: Why 126 Kts Selected?

Sat Jul 16, 2005 4:29 am

From the speed bug configuration on the airspeed indicator.... it looks like its V2+10 thats bugged..
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RODOL
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RE: Why 126 Kts Selected?

Sat Jul 16, 2005 5:34 am

Thanks gents, that makes sense now.... cool 
 
meister808
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RE: Why 126 Kts Selected?

Sat Jul 16, 2005 4:39 pm

Here's my question... how usual is it to see 45-46 KIAS sitting at the holdshort line? I know that they may be feeling some winds(but hopefully not too much, because the nose is pointed downwind based on landing traffic), and I know that the Airspeed Indicator doesn't need to be accurate below flying speeds(what is the rule on that, because I don't know, and probably should), but 46 knots is a pretty significant error for sitting still, I think.

-Meister
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
 
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Jetlagged
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RE: Why 126 Kts Selected?

Tue Jul 19, 2005 11:59 pm

ASI's do not read very low airspeeds because the pitot static system lacks accuracy below 60 knots. IAS will be badly affected by crosswinds and gusts and will not be much use. I believe the IAS digital counters probably have a minimum endstop at the value indicated to stop them bouncing around uselessly.

The main ASI pointers are also on their endstops, just below the 60 knot mark. You'll notice the standby ASI is sitting on its minimum mark too.

Above 60 knots the speed indication is much more accurate and less affected by crosswinds. All the crew need to note is that the indication is increasing towards the first speed call at 80 knots.

For taxiing there's a groundspeed readout on EFIS, which does read down to zero.
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wing
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RE: Why 126 Kts Selected?

Wed Jul 20, 2005 1:45 am

Quoting Meister808 (Reply 4):
Here's my question... how usual is it to see 45-46 KIAS sitting at the holdshort line? I know that they may be feeling some winds(but hopefully not too much, because the nose is pointed downwind based on landing traffic),

It has nothing with the winds,45 is the lowest speed that the ASI shows,it comes alive after that speed.
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meister808
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RE: Why 126 Kts Selected?

Sat Jul 23, 2005 10:58 am

That answers my question perfectly. I'm used to flying airplanes where 45 kts. is still usable to fly with.  Cool

-Meister
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
 
zeekiel
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RE: Why 126 Kts Selected?

Thu Jul 28, 2005 11:32 am

Quoting Wing (Reply 6):
It has nothing with the winds,45 is the lowest speed that the ASI shows,it comes alive after that speed.

Do some airlines have the PNF call "Airspeed Alive" when the IAS starts moving?

Cheers

Zeekiel
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sprout5199
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RE: Why 126 Kts Selected?

Fri Jul 29, 2005 2:38 am

Quoting Zeekiel (Reply 8):
Do some airlines have the PNF call "Airspeed Alive" when the IAS starts moving?

I say that to myself(maybe out loud also?) when I fly (c-152). just one of those mental checks I do.

Dan in Jupiter
 
wing
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RE: Why 126 Kts Selected?

Fri Jul 29, 2005 2:58 am

Quoting Zeekiel (Reply 8):
Do some airlines have the PNF call "Airspeed Alive" when the IAS starts moving?

We don't have a call of "airspeed alive" in our SOP, I cant comment on the other airlines since I dont know.100 kts is the speed check call that we do.
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