V2
Folks,
Lead Balloon puts it well, and there is no divide between Boeing (or Airbus) and the FAA certification rules.
There might be lots of detail in how a number is derived, but in the cockpit KISS is the golden rule, and for V1, it is the go speed, NOT the decision speed.
I have been "up front" for two critical EFATOs ( and a few less critical for stopping) one a go, one a stop, both involving instantaneous mechanical re-arrangement of an engine (always an outboard to maximize directional problems - as dictated by our old mate Murphie) KISS is the ONLY consideration.
Tootle pip!!
PS: If you listen carefully, the Boeing video has it right.
Lead Balloon puts it well, and there is no divide between Boeing (or Airbus) and the FAA certification rules.
There might be lots of detail in how a number is derived, but in the cockpit KISS is the golden rule, and for V1, it is the go speed, NOT the decision speed.
I have been "up front" for two critical EFATOs ( and a few less critical for stopping) one a go, one a stop, both involving instantaneous mechanical re-arrangement of an engine (always an outboard to maximize directional problems - as dictated by our old mate Murphie) KISS is the ONLY consideration.
Tootle pip!!
PS: If you listen carefully, the Boeing video has it right.
During the Sim ride in the video, the commentary says "you must initiate maximum braking by V1". Is that correct?
Is "initiating" maximum braking the same as actually achieving maximum braking?
What happens if you "initiate" maximum braking "by" V1 but you nonetheless exceed V1? Do you have another decision to make?
Is "initiating" maximum braking the same as actually achieving maximum braking?
What happens if you "initiate" maximum braking "by" V1 but you nonetheless exceed V1? Do you have another decision to make?
V1 is defined as the pilot's initiation of the first action (e.g., applying brakes, reducing thrust, deploying speed brakes)
You're playing with words. Initiating is not the same as achieving, and should be obvious - look up a dictionary if in doubt.
No. Continue the reject. The aircraft accelerating past V1 with the thrust from the good engine/s prior to them achieving idle/reverse is taken into account. Note that reverse though is not on its own taken into account when the aircrafts reject ability is certified, it's just a "bonus" item.
Is "initiating" maximum braking the same as actually achieving maximum braking?
What happens if you "initiate" maximum braking "by" V1 but you nonetheless exceed V1? Do you have another decision to make?
I'm not playing with words. I'm focussing on what appears to be a possible source of confusion.
So you've confirmed that you have the same view as I have as to the distinction between "initiating" and "achieving". And you have the same view as I have as to the possibility of exceeding V1 during a 'normal' take off rejection action.
Let us assume that you "initate" maximum braking at or before V1, but you detect that you are "achieving" no braking and you exceed V1. Do you really "continue to reject"?
So you've confirmed that you have the same view as I have as to the distinction between "initiating" and "achieving". And you have the same view as I have as to the possibility of exceeding V1 during a 'normal' take off rejection action.
Let us assume that you "initate" maximum braking at or before V1, but you detect that you are "achieving" no braking and you exceed V1. Do you really "continue to reject"?
Last edited by Lead Balloon; 20th Dec 2016 at 06:31.
Megan,
Please go and look up the proper certification definitions, please, not popular shibboleths. It is really quite important in the understanding of what V1 actually is, as opposed to popular misconceptions.
Please use authoritative documents, not common "text books", FCOMs etc.
That is when you are really on your own, but by that time the thrust levers will long since be at idle ( or should be) ----- there are a number of instance over the years of something like this, not necessarily an engine failure, sorry, but I don't have references, but the outcome was never a happy one.
Tootle pip!!.
Please go and look up the proper certification definitions, please, not popular shibboleths. It is really quite important in the understanding of what V1 actually is, as opposed to popular misconceptions.
Please use authoritative documents, not common "text books", FCOMs etc.
Let us assume that you "initate" maximum braking at or before V1, but you detect that you are "achieving" no braking and you exceed V1. Do you really "continue to reject"?
Tootle pip!!.
Please go and look up the proper certification definitions
popular shibboleths
What happens if you "initiate" maximum braking "by" V1 but you nonetheless exceed V1? Do you have another decision to make?
Let us assume that you "initate" maximum braking at or before V1, but you detect that you are "achieving" no braking and you exceed V1. Do you really "continue to reject"?
Please read what is posted and the order in which the posts are posted.
You are "on your own"? Really? That's the collective wisdom of the experts? Really?
That might explain all those crumpled, busted and wet airframes in the video.
On my reading of the FAR definition and its underlying rationale, and on my understanding of the laws of physics, the answer to my question seems obvious: If you decide to reject and "initate" maximum braking at or before V1, but you detect that you are "achieving" no braking and you exceed V1, you 'unmake' your decision to reject.
Otherwise, the outcome is a certain overrun and another crumpled, busted or wet airframe, is it not?
That might explain all those crumpled, busted and wet airframes in the video.
On my reading of the FAR definition and its underlying rationale, and on my understanding of the laws of physics, the answer to my question seems obvious: If you decide to reject and "initate" maximum braking at or before V1, but you detect that you are "achieving" no braking and you exceed V1, you 'unmake' your decision to reject.
Otherwise, the outcome is a certain overrun and another crumpled, busted or wet airframe, is it not?
So you are proposing that braking is initiated but the brakes don't work?
I can't think of anyone who would brake without simultaneously retarding the thrust levers. Or are you suggesting that in a reject you would apply the brakes, analyse whether they are working or not, then retard the thrust levers, see if that worked, then pop the spoilers? At each point in time you make a new decision?
I can't think of anyone who would brake without simultaneously retarding the thrust levers. Or are you suggesting that in a reject you would apply the brakes, analyse whether they are working or not, then retard the thrust levers, see if that worked, then pop the spoilers? At each point in time you make a new decision?
So you are proposing that braking is initiated but the brakes don't work?
The assumptions of my question were that the reject decision was made at or before V1, braking was initiated but the brakes don't work at all and you're now over V1. If you like, add the assumption that the thrust levers were also retarded at or before V1.
But you're over V1.
Are you proposing that the only option is to look ahead and crash visually? Is that not the inevitable consequence of being over V1 and not taking off?
Absolutely no option to advance the thrust levers for the good engine/s?
Well if the stop things don't work then you're on you're own, do whatever you think is the safest option. You're now outside the certification parameters and there are no right or wrong answers.
Absolutely no option to advance the thrust levers for the good engine/s?
You're between a rock and a hard place.
Has there ever been a reject where the brakes failed to work?
Gosh. Questions in response to questions. I'm not the expert. You are, aren't you?
I realise you don't want to say it, but you're implicitly saying that the only option is to continue rolling down the runway with the thrust levers retarded, and look ahead and crash visually. I'm merely testing that position.
Certified 'big jet' engines these days must go from not much thrust to 95% rated thrust in 5 seconds or less: FAR 33.73(d):
In the conditions assumed in my scenario, will the engines really have spooled down to idle in the period between you initiating braking and retarding the thrust levers, and realising the brakes aren't working?
You've initiated braking and retarded the throttles at or before V1. Let's say 2 seconds later you realise the brakes aren't working.
The good engine/s didn't spool down to idle in those 2 seconds.
Let's say another second to advance the the thrust levers.
Note the 3 second margin that's built into the V1 certification data.
Are you still going to leave the thrust levers retarded and just look ahead and crash visually?
I realise you don't want to say it, but you're implicitly saying that the only option is to continue rolling down the runway with the thrust levers retarded, and look ahead and crash visually. I'm merely testing that position.
Certified 'big jet' engines these days must go from not much thrust to 95% rated thrust in 5 seconds or less: FAR 33.73(d):
(b) From the fixed minimum flight idle power lever position when provided, or if not provided, from not more than 15 percent of the rated takeoff power or thrust available to 95 percent rated takeoff power or thrust in not over 5 seconds. The 5-second power or thrust response must occur from a stabilized static condition using only the bleed air and accessories loads necessary to run the engine. This takeoff rating is specified by the applicant and need not include thrust augmentation.
You've initiated braking and retarded the throttles at or before V1. Let's say 2 seconds later you realise the brakes aren't working.
The good engine/s didn't spool down to idle in those 2 seconds.
Let's say another second to advance the the thrust levers.
Note the 3 second margin that's built into the V1 certification data.
Are you still going to leave the thrust levers retarded and just look ahead and crash visually?
Join Date: Mar 2007
Location: Look up and wave
Posts: 359
Likes: 0
Received 0 Likes
on
0 Posts
You guys need to get a room seriously.
If serious **** happens and you haven't heard V1 - stop. If your hands off the thrust levers - go!
If it's not a critical failure I'd rather get airborne and land with all the runway in front of me than reject at high speed with the end of the runway much closer than I'd like. Even if an engine dumped its guts.
If serious **** happens and you haven't heard V1 - stop. If your hands off the thrust levers - go!
If it's not a critical failure I'd rather get airborne and land with all the runway in front of me than reject at high speed with the end of the runway much closer than I'd like. Even if an engine dumped its guts.
In the scenario I provided you have heard V1. At or before the point at which you heard V1, you initiated braking and retarded the thrust levers.
2 seconds after you initiated braking and retarded the thrust levers you realise the brakes are not working. You are now over V1 and the engines are spooling down.
Do you:
(1) un-make your decision to reject, advance the thrust levers and attempt to take off, or
(2) look ahead and crash visually.
Those seem to me to be the only options. The availability of (1) would seem to me (as a non-expert) to depend mostly on how much the good engine/s would have spooled down in the seconds between retarding the thrust levers and the realisation that the brakes have failed (2 or 3 seconds), and how long it would take the good engine/s to deliver sufficient take off thrust after advancing the thrust levers a second later.
Somebody in PPRuNeland must have experience in how much a 'modern big jet' engine spools down in 3 seconds and how long it takes to return to full thrust if the thrust lever is advanced at second 4. (And by 'modern big jet' I don't mean a B707...).
2 seconds after you initiated braking and retarded the thrust levers you realise the brakes are not working. You are now over V1 and the engines are spooling down.
Do you:
(1) un-make your decision to reject, advance the thrust levers and attempt to take off, or
(2) look ahead and crash visually.
Those seem to me to be the only options. The availability of (1) would seem to me (as a non-expert) to depend mostly on how much the good engine/s would have spooled down in the seconds between retarding the thrust levers and the realisation that the brakes have failed (2 or 3 seconds), and how long it would take the good engine/s to deliver sufficient take off thrust after advancing the thrust levers a second later.
Somebody in PPRuNeland must have experience in how much a 'modern big jet' engine spools down in 3 seconds and how long it takes to return to full thrust if the thrust lever is advanced at second 4. (And by 'modern big jet' I don't mean a B707...).
Join Date: Mar 2007
Location: Look up and wave
Posts: 359
Likes: 0
Received 0 Likes
on
0 Posts
Lead balloon,
In that scenario you're having a pretty bad day. You'd have full reverse available (in fact you've probably already deployed them when you said stop) on whatever engine(s) are turning and you'd then run through the recall items for loss of braking.
Once you've committed to stopping, you've committed.
In that scenario you're having a pretty bad day. You'd have full reverse available (in fact you've probably already deployed them when you said stop) on whatever engine(s) are turning and you'd then run through the recall items for loss of braking.
Once you've committed to stopping, you've committed.