Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Calling V1 Early vs Vmcg

Tech Log The very best in practical technical discussion on the web

Calling V1 Early vs Vmcg

Old 16th Dec 2011, 21:49
  #21 (permalink)  
 
Join Date: Apr 2008
Location: A tropical island.
Posts: 460
PEI, you're worried about getting everything down to the n-th degree and it's just not going to happen. In the big picture (and in the real world) when you're within 5 knots of V1 you might as well be at V1 as far as decision making is concerned (since we are not lowering V1, just the V1 call). Above all else, though, don't forget to fly the aircraft, if you need to reduce power and/or stop above V1 because it can't be controlled then do so.

As you mentioned, there are a lot of variables in aviation, but contrary to what you said, not all of them can be known/accounted for (there are simply too many).

Your last statement is rather confusing though. A greater level of understanding and learning is achieved from perceptions (experience) and grouping those perceptions into insights (understanding). Too often pilots become mired and obsessed with minor and unimportant aspects of an issue. Reminds me of the phrase "losing sight of the forest but finding the trees".

There is a Boeing training video which goes into great detail of what all the V speeds are and how they effect you, as well as how being above/below them effect the aircraft.

Finally, while Vmcg is a concern as far as flying the aircraft, short of the engine falling off the wing or simply disintegrating it will continue to produce some power for several seconds after the point of "failure" as it spools down. In the case of an engine fire, full (or nearly so) power. We can throw what ifs around all day to get this thing down to the n-th degree, but still, at the end of that day, 5 knots early (for the call) is not a big deal.

Last edited by aviatorhi; 17th Dec 2011 at 05:42. Reason: spelling
aviatorhi is offline  
Old 16th Dec 2011, 22:07
  #22 (permalink)  
 
Join Date: Oct 2010
Location: Germany
Age: 43
Posts: 395
gents, again- the idea of starting the callout a little early is to reach the actual v1 speed when you have spoken out the "vee one" phrase. and since its a little slippery procedure e.g lufthansa as well their daughter companies do not call out "vee one" but "go" at the actual v1 speed. spelling go is faster than vee one and the procedure is that when when you start to hear the go the procedure is just to go.

so the guy the thread opener spoke to is spot on- not the v1 is lovered but just the callout is spoken a second earlier , thats all the secret about this whole discussion.

"Weellllll, we don't really lower V1, we just call it early."
aerobat77 is offline  
Old 17th Dec 2011, 14:55
  #23 (permalink)  
Thread Starter
 
Join Date: Oct 2006
Location: Ankh Morpork, DW
Posts: 602
so the guy the thread opener spoke to is spot on- not the v1 is lovered but just the callout is spoken a second earlier , thats all the secret about this whole discussion.

"Weellllll, we don't really lower V1, we just call it early."
Yes, that might have been the intent, but in practice it's treated as though V1 has been lowered. Captains remove their hand from the TLs at V1-5.
ImbracableCrunk is offline  
Old 17th Dec 2011, 22:58
  #24 (permalink)  
 
Join Date: Mar 2006
Location: England
Posts: 879
Aviatorhi, re ‘not worrying about getting to the nth-degree’.
‘Worrying’ (a state of constant concern) is an essential aspect of aviation safety; it’s not about how much you can get away with – its considering what safety margin there is, are you within that margin and is there something spare for the unknown.

The early V1 problem isn’t one of technical prowess or moral principles, it about attitude.
With an “I know better” attitude – ‘that little bit doesn’t matter, it’s not a big deal’; … then what does matter? For that you have to be able to define the limiting point and thus you need to know how the issue is derived and the consequences of any deviation.

You learn through perception, but how do you know that all perceptions and experiences are justified, or of high quality to be kept as valid experience. Perceptions have to be ‘explored’, checked, and compared before you can claim insight, understanding, and knowledge.
An ‘I know better’ attitude is a major obstruction in this process – ‘those little checks and comparisons don’t matter’.
Similarly, ‘it won’t happen to me’ attitude - it’s just not going to happen:- invulnerability?
Experience should tell you that ‘it’ happens, and when it does you have to be prepared; this means not having to considering whether you act or not at a particular speed. Continuing when ‘just below’ V1 may result in a visit to the edge of the runway, hitting runway light or clipping a wing; stopping ‘just above’ V1 may end up in the mud – plenty of time to consider the correct action then.

An assumption that the engine will ‘probably’ continue to produce thrust after failing is pure supposition – in an event, you don’t know; and what about prop malfunctions, critical engine, crosswind, or a very wet runway, you have to consider the worst case and plan for that. Some, but not all are built into the regulations.

… "losing sight of the forest but finding the trees".
When walking through a forest, knowledge of the trees (a hazard) is useful for avoiding them.
Conversely, knowledge of the clear spaces provides a safe path through the forest.
I prefer to look for both.
PEI_3721 is offline  
Old 18th Dec 2011, 02:33
  #25 (permalink)  
 
Join Date: Oct 2010
Location: Germany
Age: 43
Posts: 395
Yes, that might have been the intent, but in practice it's treated as though V1 has been lowered. Captains remove their hand from the TLs at V1-5.
thats maybe not so good. basicly you should be "stop orientated" until positivly above V1 when something bad happens.

on the other hand such discussions are here mostly provided with pure theoretical knowledge by published and written down procedures on the internet . but an actual situation in real live is not just procedures and written down technical knowledge. and aircraft was not able , is not able and will not be able to fly by just theoretical procedures at such critical situations.

having an engine failure at nearly V1 with simultany a vmcg very close to this speed is of course a serious and a very rare thing. like said- 99.99% never had this in their entire career. when it happens its up to the PIC what he does and nothing that can be written here will help you.

by the book and a pure theoretical discussion he may be slightly wrong removing his hand ( and decide to be "go" orientated) 5 knots early.

by real live he will be jugded by the outcome of this situation when truly at nearly exact the edge of v1 and simulatany vmcg very close to this speed an engine suddenly blows , whatever he does, putting his hand back on the lever and abort or try to go.

best regards
aerobat77 is offline  
Old 18th Dec 2011, 05:54
  #26 (permalink)  
 
Join Date: Apr 2008
Location: A tropical island.
Posts: 460
PEI,

As I stated... maintain control of the aircraft, this thread is discussing absolutes regarding an environment which is not absolute. The CAs responsibility is to maintain control of the A/C if that means putting their hands on the throttles after the V1 call, well, so be it. Making the call prior 5 knots prior is acceptable as far as decision making is concerned. Remember, AVIATE, NAVIGATE, COMMUNICATE.
aviatorhi is offline  
Old 18th Dec 2011, 16:45
  #27 (permalink)  
 
Join Date: Nov 2011
Location: Somewhere
Posts: 52
I suspect calling V1 prior to V1 is about getting ahead of the call out, given all the evidence of bad decision making on the roll.

With the preponderance of flex, putting all the runway behind you folks, it's become more critical to get the RTO performed at exactly the right time, as you have taken away all safety margin ahead of you.

Wouldn't a max take off, with miles of runway ahead of you preclude the need for such 'tweaking' of the call outs?
RainingLogic is offline  
Old 18th Dec 2011, 17:05
  #28 (permalink)  
 
Join Date: Oct 2005
Location: FL350
Age: 36
Posts: 22
i was flying 747 classics n in our company we had a standard practice of reducing v1 by 5 knots but then there was a limit it was never below Vmcg,offcourse v1 can never be les then Vmcg
RAM777 is offline  
Old 18th Dec 2011, 17:29
  #29 (permalink)  
 
Join Date: Jul 2011
Location: UK
Posts: 56
offcourse v1 can never be les then Vmcg
I could be wrong but I'm sure an ex C130 guy told me this isn't the case on the Herc.
corporate-pilot is offline  
Old 18th Dec 2011, 17:45
  #30 (permalink)  
 
Join Date: Dec 2002
Location: UK
Posts: 2,047
corporate-pilot, this may have been a particular military application where ‘at risk’ periods are accepted.
There was (still is?) a few rare civil applications which use a Vstop and Vgo for contaminated operations. This results in a small speed range in which a safe stop cannot be achieved and it is also unsafe to go because of the Vmcg limit, i.e. the operation accepted the risk of an overrun; thus it would be limited to specific runways.
safetypee is offline  
Old 19th Dec 2011, 05:37
  #31 (permalink)  
Moderator
 
Join Date: Apr 2001
Location: various places .....
Posts: 6,590
particular military application where ‘at risk’ periods are accepted

A number of examples exist in practice.

For instance, STOL certification is not embraced by civil regulators as far as I am aware. MIL, on the other hand, requires this capability for some platforms to do what they need to do.

It follows that the military spend a lot more time and effort on flight test work up to operational release than is necessary for civil Types.

Horses for courses.
john_tullamarine is offline  
Old 19th Dec 2011, 08:31
  #32 (permalink)  
 
Join Date: Oct 2010
Location: Germany
Age: 43
Posts: 395
iwas flying 747 classics n in our company
ram777, that is with your now 27years age without any doubt a stunning performance ! what do you fly now? 747-400, A380 leftseat ?
aerobat77 is offline  
Old 19th Dec 2011, 08:33
  #33 (permalink)  
 
Join Date: Apr 2005
Location: Australia
Posts: 1,419
Seems to me that all you are doing is ensuring that the V1 call is completed AND understood by the PF by the time the speed reaches V1 which is entirely as it should be.
Precisely. I have observed literally hundreds of V1 calls in the simulator and thinking about it now, I would say the vast majority were called three to five knots after the ASI needle had gone through V1. This is due to the rate of acceleration and the PM not calling until V1 or shortly after. I have never seen V1 called before the ASI needle reached V1 - so the error is always when the speed is accelerating fast.

Despite tolerances built into the V1 speed I believe a call 5 knots prior to V1 of V1 is a commonsense pragmatic approach. Anyone aborting within 10 knots of V1 is asking for trouble based upon past history of the dangers of high speed aborts. Personal opinion only, of course
A37575 is offline  
Old 19th Dec 2011, 08:37
  #34 (permalink)  
 
Join Date: Apr 2005
Location: Australia
Posts: 1,419
Remember, AVIATE, NAVIGATE, COMMUNICATE.
Maybe I am the classic grumpy old man but I bloody HATE that hackneyed phrase which has been regurgitated for years and years and bloody years. It reminds me of some religious liturgy mouthed by the faithful masses to ward off the Evil Eye
A37575 is offline  
Old 19th Dec 2011, 10:01
  #35 (permalink)  
 
Join Date: Apr 2008
Location: A tropical island.
Posts: 460
@A37575

Sorry about that, I have the same pet peeve with with the phrase "be professional" (or any variation thereof).

Anyway, the point I was making is that regardless of what anyone verbally states in the cockpit flying the airplane comes first. The example I like is when I see pilots driving past Vr (and approaching V2 quite rapidly) and still not rotating... only because the guy next to them missed the Vr call.
aviatorhi is offline  
Old 19th Dec 2011, 12:06
  #36 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,581
Everyone seems to forget/ignore/?not know? (whatever) the fact that the V1 and Vr calls by PNF are not 'action' calls but backup and crosscheck calls and that PF is EXPECTED to KNOW when he/she is at V1 and Vr and take action accordingly.. That's what the 'F' in PF means.
BOAC is offline  
Old 19th Dec 2011, 21:07
  #37 (permalink)  
Thread Starter
 
Join Date: Oct 2006
Location: Ankh Morpork, DW
Posts: 602
So, can we agree that V1 should not be called below Vmcg in a B737?
ImbracableCrunk is offline  
Old 19th Dec 2011, 21:12
  #38 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,581
One sincerely hopes that is writ in your SOPs? Oh yes, I forgot, when your lot call it they don't mean V1, do they, they mean V1-5/'gee here comes V1', so that's ok and I guess it is ok to call it (but not with me).

Why not ask your FOI if he is happy with this?
BOAC is offline  
Old 19th Dec 2011, 21:16
  #39 (permalink)  
 
Join Date: Mar 2001
Location: I wouldn't know.
Posts: 4,126
@IC i would agree, however the automatic callout on the 737 comes early as well.
Denti is offline  
Old 20th Dec 2011, 01:08
  #40 (permalink)  
Thread Starter
 
Join Date: Oct 2006
Location: Ankh Morpork, DW
Posts: 602
BOAC wrote:
One sincerely hopes that is writ in your SOPs? Oh yes, I forgot, when your lot call it they don't mean V1, do they, they mean V1-5/'gee here comes V1', so that's ok and I guess it is ok to call it (but not with me).

Why not ask your FOI if he is happy with this?
My thought is that since some CAs take their hands off of the TLs at the V1 call like they've been burned, it's not a, "Here it coo-ooomes," but rather a limit.

I thought I'd do the relatively anonymous thing and ask the PPRuNe Tribe for thoughts before I go beyond annoying a few instructors.
ImbracableCrunk is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.