Jump to content
Sign in to follow this  
dlh737

Speed BUG V2 + 20 - Error?!?

Recommended Posts

Good afternoon, In the last few days, after few test on yours excellent 737NGX during take off.... I discovered a strange process during T/O that create a discrepancy between MCP speed and speed BUG on ASI of exactly 20 KTS. As explained into the manual (FCOM 2 - 4.20.13 - Page 223): • MCP IAS/Mach display and airspeed cursor change to V2 + 20 knots but during my takeoffs, only the magenta speed bug on PFD increse of 20 KTS (V2+20), the MCP speed remain at V2. When at "acceleration height" I check the speed in order to increse it to the Flaps UP speed, I discover the A near the flashing speed that was still at V2. Then, once I increased the speed on MCP the magenta bug remainedt 20 Kts over my new selection. Please confirm me if someone else experience this problem and let me know if is my mistake understanding the manual or is really an issue.... Thanks for your coopertion.... and for the excellent product.

Share this post


Link to post
Share on other sites
Good afternoon, In the last few days, after few test on yours excellent 737NGX during take off.... I discovered a strange process during T/O that create a discrepancy between MCP speed and speed BUG on ASI of exactly 20 KTS. As explained into the manual (FCOM 2 - 4.20.13 - Page 223): • MCP IAS/Mach display and airspeed cursor change to V2 + 20 knots but during my takeoffs, only the magenta speed bug on PFD increse of 20 KTS (V2+20), the MCP speed remain at V2. When at "acceleration height" I check the speed in order to increse it to the Flaps UP speed, I discover the A near the flashing speed that was still at V2. Then, once I increased the speed on MCP the magenta bug remainedt 20 Kts over my new selection. Please confirm me if someone else experience this problem and let me know if is my mistake understanding the manual or is really an issue.... Thanks for your coopertion.... and for the excellent product.
You're not following the 'MCP SPD" your following the PFD commanded SPD of V2+20 set from the MCP SPD window. MCP SPD is set to V2. After that you're at accel height and raising flaps etc...

Share this post


Link to post
Share on other sites

I tryed to give an explanation regarding the discrepancy between my MCP speed and the magenta BUG.... untill I'm force to engage an A/P mode in order to solve the problem. I don't like AP for takeoff and so I left everything off untill cruise or at the end of the SID. The problem in effect is not follow the magenta bug V2+20 the problem is later when I need to set the Bug UP speed or still later that I have a dicrepancy betwwen them. And why is in the manual written MCP speed AND airspeed cursor change to V2+20.... Do I miss something? Thanks

Share this post


Link to post
Share on other sites

Maybe I'm just misreading this section, but to me it the manual is saying you'll get the MCP display increase to V2 + 20 knots only after the engagement of an autopilot. I could be reading it wrong, but that's how it reads to me. This is straight from the PMDG installed FCOM2. Under the "[Option - Automatic thrust reduction after takeoff, FMC update 10.1 and later]" which is what we have, you get:

flight director engaged status is terminated by engaging an autopilot in CMD (CMD replaces FD in A/P status display)
And indented under that, you get:
pitch engages in LVL CHG and pitch mode FMA is MCP SPD unless another pitch mode has been selectedMCP IAS/Mach display and airspeed cursor change to V2 + 20 knotsroll mode engages in HDG SEL unless another roll mode has been selected.

Share this post


Link to post
Share on other sites

So.... it is impossible fly manually the airplane whitout FD and AP...... I need to engage AP.... I did MCC on 737 and never happen..... but probably is an option on the 737...... Sorry for my not understanding..... but I'm preparing myself for selection and I would like to understand if it was my mistake.... Really thanks for your quick answer!

Share this post


Link to post
Share on other sites

If you're manually flying takeoff (of course you are) you set MCP V2 SPD into the MCP window. In the older FMC U.XX software - once you engaged the A/P in CMD the commanded SPD was MCP SPD +20 regardless of the pitch mode. Otherwise we see THR HLD/ N1| LAT MODE YOUR CHOICE| TO/GA | At takeoff with no CMD A/P engaged you should see magenta set to MCP SET SPD ONLY. Once you engage the A/P in CMD (Your choice) you should see the magenta cursor set to + MCP SPD + 20. If you engaged CMD without VNAV you should not have flaps UP SPD displayed on the PFD on the magenta BUG (The flaps 1 SPD) but remaining at the MCP SPD. Of course changes to the FMC software could have changed so we must always double check to see if that is the case.

Share this post


Link to post
Share on other sites

Really thanks guys for your patience The first two point are exactly what I can see and do..... NO A/P - FMA: THR HLD/ N1| | TO/GA | At acceleration height I call PNF BUG UP speed without any AP command or VNAV or LVL CHG.... the magenta bug is at V2 + 20 and the MCP at V2.... so when my PNF select on the MCP the BUG UP (Speed indicated on PFD ex 220) on my MCP he set 220 but the bug on PFD is at 240.... That's never happend to me.... and why I ask support to you.... Still sorry im%20Not%20Worthy.gif P.S.: I personally never saw a discrepancy between BUG on PFD and MCP select speed (normally an AP mode as VNAV remove the speed from the box.... but if I see the select speed the magenta bug must match it) Am I wrong?

Share this post


Link to post
Share on other sites

hmm i must be a clown as i also find it difficult to understand. Normally with other 737 i have FD/on , AT/on, TO/GA/on and V2 for instance 154 in MCP. After takeoff and hitting A/P at 400 feet or later should i get 174knots in PDF AND the MCP ? It still gives me 154 in both and A154 in the MCP Michael


Michael Moe

 

fs2crew_747_banner1.png

Banner_FS2Crew_Emergency.png

Share this post


Link to post
Share on other sites

Roberto,Let me see if I'm understanding correctly:You're saying that at acceleration height the MCP speed window and the PFD speed bug should be synchronized even if you're still in TO/GA mode? All the documentation we have shows TO/GA pitch mode command speed being MCP+20 until you engage another pitch mode. Very easy to change but we need confirmation that the NGX is actually wrong - one of our tech advisiors is pretty sure the MCP on his company's airplanes does not sync with the bug until you exit TO/GA mode, but he's not back to work to check for sure until next week.


Ryan Maziarz
devteam.jpg

For fastest support, please submit a ticket at http://support.precisionmanuals.com

Share this post


Link to post
Share on other sites
hitting A/P at 400 feet or later should i get 174knots in PDF AND the MCP ? Michael
Why would the MCP SPD window change? The MCP window is manually set to V2. It is not set to V2+20 nor does it change to that.

Share this post


Link to post
Share on other sites
Why would the MCP SPD window change? The MCP window is manually set to V2. It is not set to V2+20 nor does it change to that.
Ok the MCP window will change to +20V2 under these conditions - You manually adjust the mcp spd knob and (one click will make it jump)You engage the A/P in cmd from TO/GA.

Share this post


Link to post
Share on other sites

I've studied with FOMs and it's quite enlightening!!Especially learned so many procedures for takeoff..I used to be a LNAV/VNAV guy.. Eh.. so, back to the topic, I found this.. the of Year 1993.http://www.pprune.or...gs-v2-20-a.htmlSeems correct PFD bug is different with MCP. (if this post is also correct one, too) Cuppa.gif

Share this post


Link to post
Share on other sites

I posted in another thread that got buried I guess that with the newest hot-fix 15AUG the magenta bug now does not jump to V2+20 but stays at V2 unless you have VNAV armed. Is this now the correct behavior on takeoff?


Sean Green

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
×
×
  • Create New...