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bueb0g
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V1 - A Danger?

Wed Oct 27, 2010 6:52 pm

Probably been discussed before, so, in advance, I apologise.

Does the V1 "decision speed" do more harm than good? Maybe not the idea of V1 itself, but the way pilots are trained with regard to it.

Is an overrun preferable to taking an unsafe aircraft into the air? Take the Concorde crash - if V1 training was different, the captain - once aware he was traling heavy flames - may well have aborted. Now, I don't know about the rest of you but I think Concorde sitting in the grass, with possibly no fatalties is better than the actual outcome of that dreadful accident.

In fact, V1 is often misleading. I remember one case where a BMI baby 737 aborted its takeoff significantly after V1, when the captain noticed the aircraft to be severely out of trim. Judging that he had enough space to stop, and deciding that if he did overunn it would be preferable to flying an uncontrolable plane, the crew was able to bring the 737 to a safe stop within the confines of the runway.

I could find countless examples of accidents where the outcome would have been less severe had the crew rejected after V1, so my question is whether it should be regarded differently? Maybe more like the Descision Height on approach - the height at which an unsafe approach must be aborted, without being a "point of no return" like V1 -as you can still go around after the DH.

I'm not totally sure, so it'd be great to find out what you guys think. I think if the rules around V1 were loosened, we would see more overunns but less accidents on climbout etc.
Views?
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777236ER
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RE: V1 - A Danger?

Wed Oct 27, 2010 7:30 pm

Quoting bueb0g (Thread starter):

Is an overrun preferable to taking an unsafe aircraft into the air? Take the Concorde crash - if V1 training was different, the captain - once aware he was traling heavy flames - may well have aborted. Now, I don't know about the rest of you but I think Concorde sitting in the grass, with possibly no fatalties is better than the actual outcome of that dreadful accident.

From the BEA report (public domain):

1.16.13.4 Consequences of Aborting the Takeoff
Two simulations of a possible acceleration-stop were performed, one based on the
aircraft’s speed when the rotation was commenced (that is to say in fact the first moment
when the crew could have been warned by unusual sensations), at 183 kt, the other at
196 kt, when the FE said what can be understood as “stop”.

The simulations were conducted with the following hypotheses:
• braking on seven wheels, to take into account the destruction of tyre No 2,
• braking torque available at nominal value until the maximum energy indicated in
the Flight Manual (70 MJ), increased by 10%,
• use of thrust reversers on engines 1, 3 and 4.
With this set of hypotheses, it appears that the residual speed of the aircraft at the end of
the runway would have been 74 kt for a takeoff aborted at 183 kt and 115 kt for a takeoff
aborted at 196 kt.
These figures show that an aborted takeoff would have led to a runway excursion at such
a speed that, taking into account the fire, the result would probably have been
catastrophic for the aircraft and its occupants.


Quoting bueb0g (Thread starter):
I could find countless examples of accidents where the outcome would have been less severe had the crew rejected after V1

I can't think of one. Name a single accident where the investigating branch has stated that aborting the take-off after V1 would have resulted in a more favourable outcome.

Quoting bueb0g (Thread starter):
In fact, V1 is often misleading. I remember one case where a BMI baby 737 aborted its takeoff significantly after V1, when the captain noticed the aircraft to be severely out of trim. Judging that he had enough space to stop, and deciding that if he did overunn it would be preferable to flying an uncontrolable plane, the crew was able to bring the 737 to a safe stop within the confines of the runway.

One example makes no difference. The calculation of takeoff performance by the manufacturers considers a number of operational parameters, which ensures that V1 secures accelerate-stop, or fly, in the worst case. For example, uncontained engine failure with subsequent system loss must allow an accelerate-stop at V1, as well as a take off.

The danger in V1 is not that aircraft are departing at continuing at V1 when they should be stopping, but rather they should be aborting at V1 when they are continuing. V1 is the brakes-on speed, not the decision speed.
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CaptainRed
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RE: V1 - A Danger?

Wed Oct 27, 2010 8:27 pm

Here is what I think about this interesting question.

Quoting bueb0g (Thread starter):
Is an overrun preferable to taking an unsafe aircraft into the air?

This is certainly a very difficult decision a cockpit crew faces when something bad happens around V1. It is definitely a very stressful situation in which the crew has to assess first what has happened and then wether it is safe to fly or better to abort with a very high probability of an overrun with all consequences. So unless it is not quite obvious that the plane is unable to fly I think every crew will first get the plane in the air and then have more time to figure out what happened before trying to return to the ground safely.

Quoting bueb0g (Thread starter):
I remember one case where a BMI baby 737 aborted its takeoff significantly after V1, when the captain noticed the aircraft to be severely out of trim. Judging that he had enough space to stop, and deciding that if he did overunn it would be preferable to flying an uncontrolable plane, the crew was able to bring the 737 to a safe stop within the confines of the runway.

I don't know which incident you are referring to, but since V1 is often defined as the speed after which the airplane cannot be stopped safely on the runway, I don't think it was that significantly over V1 (or maybe V1 wasn't calculated correctly). Obviously here the crew made the right decision, well done.

You may have already seen this video, it is a great example of a well handled emergency situation that happend during takeoff above V1:
http://www.flightlevel350.com/Aircra...homsonfly_Aviation_Video-8457.html

Quoting 777236ER (Reply 1):
From the BEA report (public domain):

Thanks for this information, interesting to read.
 
Woof
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RE: V1 - A Danger?

Wed Oct 27, 2010 9:07 pm

My understanding is that after V1, apart from failures which will obviously result in a crash (stuck primary controls, total loss of power, wing falling off) it is statistically safer to fly than to try and abort.

If you fly you are likely to have more time to deal with the incident.

If you don't fly you are going to have an accident regardless.

You just don't have the time to go through a checklist and make an informed decision before the decision gets made for you (ie the runway ends).
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CosmicCruiser
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RE: V1 - A Danger?

Wed Oct 27, 2010 10:46 pm

Quoting bueb0g (Thread starter):
I think Concorde sitting in the grass, with possibly no fatalties is better than the actual outcome of that dreadful accident.

I can't believe you assume that the Concorde would be sitting in the grass after the mentioned abort.
 
Woof
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RE: V1 - A Danger?

Wed Oct 27, 2010 10:51 pm

Quoting CosmicCruiser (Reply 4):
I can't believe you assume that the Concorde would be sitting in the grass after the mentioned abort.

Especially as V1 on Concorde was around 150 knots. I would think there might be bits of Concorde on the grass though.
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tb727
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RE: V1 - A Danger?

Wed Oct 27, 2010 11:13 pm

Get the plane into the environment it was designed to be in and deal with it from there. Unless it's catastrophic with loss of control there is nothing else you should do. High speed aborts, even below V1, are a bad idea.
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cpd
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RE: V1 - A Danger?

Wed Oct 27, 2010 11:28 pm

Quoting bueb0g (Thread starter):
Is an overrun preferable to taking an unsafe aircraft into the air? Take the Concorde crash - if V1 training was different, the captain - once aware he was traling heavy flames - may well have aborted.

Going airborne was the only chance. Concorde was beyond V1 at that point and would have overrun the runway at high speed.

The severity of the fire and the surging engines made any escape impossible. The speed was always too low. And even the slightly early (and slower) rotation would have made little difference. The incident was a number of one-in-a-million factors all coming together to make an impossible situation.

I once tried similar in a simulator with a fairly realistic Concorde. Although I couldn't simulate some of the effects, the ultimate result was the same - speed was too low, couldn't climb high enough - no escape. That's not scientific - but it's indicative of just how catastrophic their situation was.

Quoting Woof (Reply 3):
You just don't have the time to go through a checklist and make an informed decision before the decision gets made for you (ie the runway ends).

And following the checklist procedures is the best way of dealing with the issues, rather than trying to make up something on the fly (which could go wrong).

[Edited 2010-10-27 16:31:40]
 
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Aaron747
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RE: V1 - A Danger?

Wed Oct 27, 2010 11:36 pm

I can't believe any ounce of logic would result in thinking along the lines of "staying on the ground is better". Airplanes are designed to be in the air and generally handle terribly on the ground. I would rather be in the air with hope of having more control over the situation than on the ground where various externalities are going to determine what happens to the aircraft - and none of them gentle unless there's a shallow pond off-runway. With some modicum of control and no heavily populated or wooded area nearby, there's at least some chance of a decent outcome provided one can control descent angle and the like. Going through concrete barriers, fencing, trees, roadways, buildings, and drainage channels recessed from the runway by gradients of 10+ feet - you do the math - the plane and everything in it will be smashed beyond recognition at anything even half of V1 speeds.
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Illini_152
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RE: V1 - A Danger?

Thu Oct 28, 2010 3:07 am

Ask DJ AM about aborts after V1 for blown tires.


Or his crew.


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lowrider
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RE: V1 - A Danger?

Thu Oct 28, 2010 3:42 am

Quoting bueb0g (Thread starter):
Is an overrun preferable to taking an unsafe aircraft into the air?

Far too many variables to make a blanket statement. What is off the end of the runway? An arrestor bed? A gas station? An ocean? Can an evacuation be conducted there with a reasonable expectation of success? Have you correctly identified the problem and are sure that an overrun is the best choice? Do you have sufficient brake energy margin to stop?

To reject beyond V1 for anything but the most catastrophic circumstances is extremely hazardous. I would only consider it for things like multiple engine failures, massive structural failure, or collision with another aircraft of vehicle. Consider this, Boeing considers rejects beyond V1 so undesirable, that on the 747-400, all cautions and warnings are inhibited from V1 to 400 ft agl or 25 sec after V1.
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Alias1024
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RE: V1 - A Danger?

Thu Oct 28, 2010 5:46 am

Quoting Lowrider (Reply 10):
To reject beyond V1 for anything but the most catastrophic circumstances is extremely hazardous. I would only consider it for things like multiple engine failures, massive structural failure, or collision with another aircraft of vehicle.

  
The only other instance I can think of for an abort above V1 would be a flight control failure. If I pull back on the controls and the airplane does nothing, the abort decisions been made for me.
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thegeek
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RE: V1 - A Danger?

Thu Oct 28, 2010 6:13 am

Quoting Illini_152 (Reply 9):
Ask DJ AM about aborts after V1 for blown tires.

Umm, he actually lived to tell the tale of that crash, but died later from drugs. And with that crash, there was another survivor too. I'd think that tire blowouts aren't severe enough a reason to abort a takeoff after V1, but I would think an on board fire may be different. The problem with AF4590 was that everyone died, and also 4 on the ground. Hard to see how NOT taking off would be worse, although we will never know for sure. The difference may be only to the 4 on the ground.
 
Vmcavmcg
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RE: V1 - A Danger?

Thu Oct 28, 2010 6:58 am

Quoting bueb0g (Thread starter):
I could find countless examples of accidents where the outcome would have been less severe had the crew rejected after V1, so my question is whether it should be regarded differently?

Please provide just one!

I can show you countless accident reports where the crew rejected prior to V1 and the aircraft sitll did not stop within the confines of the runway. Both Boeing and Airbus have a philosophy where above 100 KIAS you will only reject for redlights, or flight control problems and the closer you get to V1 the fewer things you will reject the thakeoff for. And there is a reason for their advice.

Let me pose a question for you. When are the V1 speeds reliable? Just think about it for a moment and I would argue the V1 speeds are only valid when the aircraft is new and on the same runway where the V1 speeds were tested. The V1 speeds are based on new brakes, new tires a known runway surface (flight test) and flight test pilots. I don't know of too many aircraft that fall into that condition. There was an AA DC-10 that rejected the takeoff well prior to V1 and couldn't stop within the runway. The NTSB was extremely critical of the entire V1 concept and the way it was used. The DC-10 had a few brakes that were at the edge of their tolerance, a couple of tires that were approaching their limits. However, the crew has no knowledge of how this fits into the entire V1 calculations.

Personally, my TO briefing is specific about what we will do above or below 100KIAS. I am convinced the best way to sort out a problem is to get the aircraft in the air and sort it out there. Structually, aircraft don't do too well when they try to become off road vehicles.
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thegeek
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RE: V1 - A Danger?

Thu Oct 28, 2010 7:16 am

Quoting Vmcavmcg (Reply 13):
When are the V1 speeds reliable? Just think about it for a moment and I would argue the V1 speeds are only valid when the aircraft is new and on the same runway where the V1 speeds were tested. The V1 speeds are based on new brakes, new tires a known runway surface (flight test) and flight test pilots. I don't know of too many aircraft that fall into that condition. There was an AA DC-10 that rejected the takeoff well prior to V1 and couldn't stop within the runway.

Great points!

Quoting Vmcavmcg (Reply 13):
The NTSB was extremely critical of the entire V1 concept and the way it was used.

What did they suggest? A fudge factor? Testing on worn brakes & tires, or what?
 
CosmicCruiser
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RE: V1 - A Danger?

Thu Oct 28, 2010 7:50 am

Granted those parameters for determining V1 or correct however having some defining speed giving the pilot a known limit that he can use when making split second decisions is all you can ask for. Otherwise we all need 12,000' runways with 2000' EMAS overruns. Unfortunately it doesn't work out like that. We usually back off say 10kts just for the above mentioned test parameters. Historically high speed aborts in jumbo jets are not successful. I believe we had the highest speed abort in a DC-10 years ago that did end successfully with only blown tires, melted brakes and a hyd fire. It could have been otherwise very easily.
Cosidering the comments on the Concorde, if that long legged, small tired jet had left the pavement I doubt very seriously if it had stayed in one or even two or three pieces. The Concorde was pretty well screwed no matter what course of action the crew took. Very sad but I don't think there was a good solution.
 
Vmcavmcg
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RE: V1 - A Danger?

Thu Oct 28, 2010 7:51 am

Quoting thegeek (Reply 14):
What did they suggest? A fudge factor? Testing on worn brakes & tires, or what?

The NTSB was very critical of the way the rejected takeoff data was validated. However, in typical political fashion they only commented on the certification and did not provide any alternatives.
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cobra27
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RE: V1 - A Danger?

Thu Oct 28, 2010 8:41 am

Again this V1  .
If you have a really long runway ahead, you could stop even at higher speed, whats the big deal? Use revers and then apply brakes. Think about it if fully loaded 747 can stop a v1 at lets say 135 knots, wouldn't I light loaded stop in a shortet distance at 150 knots? I was asked that question on interview, and he specifically said LONG runway so I said yes cou can stop and he was happy. Am sure that some by the book guy wont agree with me
 
thegeek
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RE: V1 - A Danger?

Thu Oct 28, 2010 9:02 am

Quoting cobra27 (Reply 17):
I was asked that question on interview, and he specifically said LONG runway

How is it possible to pass V1, without passing Vr, on a "LONG" runway?
 
Vmcavmcg
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RE: V1 - A Danger?

Thu Oct 28, 2010 9:32 am

Quoting cobra27 (Reply 17):
Think about it if fully loaded 747 can stop a v1 at lets say 135 knots

I can assure you V1 is much higher that 135.

Quoting cobra27 (Reply 17):
so I said yes cou can stop and he was happy. Am sure that some by the book guy wont agree with me

So, did you get the position? What is wrong with being a "by the book guy"? I can assure you if you were sitting opposite of me on an interview and you answered with that answer, you wouldn't get far. To reject above V1 does not make any sense at all.
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DH106
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RE: V1 - A Danger?

Thu Oct 28, 2010 12:50 pm

Quoting Vmcavmcg (Reply 13):
Quoting bueb0g (Thread starter):
I could find countless examples of accidents where the outcome would have been less severe had the crew rejected after V1, so my question is whether it should be regarded differently?

Please provide just one!

AA191 at Chicago, 1979?
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Pihero
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RE: V1 - A Danger?

Thu Oct 28, 2010 12:54 pm

There is a definite tendancy on this forum to re-invent aviation and it's quite worrying as those interventions are no longer in the "I'm going to ask a question" domain but in the realm of " I fly FS9 and I know it all "
That v1 question has been about since the US produced a jet airliner and the concept, although since modified has staid with us as one of the main safety factors of our industry.
There is no way the basic philosophy is going to be put into question ANYMORE : before V1, one could abort, after V1, one continues the takeoff procedure. And that's that.
I remember some thirty years ago all these conferences about how "[i]being go-minded" improved flight safety, I still remember the work done on CRM and the best way to pass the safety message on a pre-takeoff briefing, and I do remember what Lowrider mentioned in his post number 10 that the manufacturers helped by "hiding" most of the cautions between ,say, 80 kt and a height of 400 ft afetr lift-off.

Quoting cobra27 (Reply 17):
I was asked that question on interview, and he specifically said LONG runway so I said yes cou can stop and he was happy. Am sure that some by the book guy wont agree with me

If your story is true, remind me never to consider letting my family fly with such a bunch of idiots, even if they have some nice prints of some gorgeously semi-naked ladies on their fuselages.

Quoting thegeek (Reply 18):
How is it possible to pass V1, without passing Vr, on a "LONG" runway

It's not possible as V1 at most equals Vr
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tdscanuck
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RE: V1 - A Danger?

Thu Oct 28, 2010 2:02 pm

Quoting Vmcavmcg (Reply 13):
The V1 speeds are based on new brakes, new tires a known runway surface (flight test) and flight test pilots.

That's not actually true...braking performance testing is done on partially worn brakes, and the worst case (MTOW RTO at V1) has to be done with fully worn brakes. With carbon brakes, the stopping performance doesn't change much with wear anyway, just the heat capacity.

I'm not sure that tire condition is specified by the FAR's, but you certainly don't change tires for every test so, on average, takeoff performance testing happens with average-wear tires.

The known runway surface is certainly true, although off-nominal surface tests are also done to correct the known surface takeoff performance data for other surfaces (grooved, wet, standing water, etc.). That should all be in the takeoff calculation on any given day.

On the flight test pilots side, that's a harder issue to deal with, but it's incorporated into the calculations by assuming a delay between the critical event (usually engine failure, but could be some other things like fire) and the rejection. So, although V1 is the decision speed for the pilots, the calculations behind it assume that the actual event happened at a slightly lower speed and that the pilots only got the chance to react by V1. In other words, the normal delay you expect from a normal pilot who's not expecting an event is built into the V1 calculation.

Quoting thegeek (Reply 18):
How is it possible to pass V1, without passing Vr, on a "LONG" runway?

You can't. As Pihero said:

Quoting Pihero (Reply 21):
It's not possible as V1 at most equals Vr

It's important to note here that, when your accel-stop decision speed (normally V1 on a balanced field calcluation) is higher than Vr, you lower V1 to equal Vr. This is to keep the procedure absolutely consistent for the pilots at all times during a critical flight phase. However, it also means you could exceed V1 (and Vr) on the ground and still have room to stop on the runway.

V1 is not always the speed at which you have to reject to stop on the runway...it *is* always the decision speed. However, most flight crews don't have the data to hand in a line environment to quickly figure out which situation you're in, and an engine failure near V1 is no time to be trying to remember if V1 was moved to match Vr or not.

The flip maneuver (raising Vr to equal V1, or at least raising it some amount above the strictly required speed to fly out at the normal V2) is an improved climb takeoff...using more runway to gain more speed. Optional on Boeing, standard on Airbus.

Tom.
 
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tb727
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RE: V1 - A Danger?

Thu Oct 28, 2010 2:03 pm

Quoting cobra27 (Reply 17):
I was asked that question on interview, and he specifically said LONG runway so I said yes cou can stop and he was happy. Am sure that some by the book guy wont agree with me

What was the interview for and who was asking and accepting that answer?
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Vmcavmcg
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RE: V1 - A Danger?

Thu Oct 28, 2010 2:22 pm

Quoting DH106 (Reply 20):
AA191 at Chicago, 1979?

I think you might want to re-read the accident report. There is no mention of rejecting above V1. The accident led to the V2+10 concept rather than taking your airspeed and if you are above V2 using pitch to achieve V2.

Quoting tdscanuck (Reply 22):
With carbon brakes, the stopping performance doesn't change much with wear anyway, just the heat capacity.

True, but the DC-10 had steel brakes.

Quoting tdscanuck (Reply 22):
On the flight test pilots side, that's a harder issue to deal with, but it's incorporated into the calculations by assuming a delay between the critical event (usually engine failure, but could be some other things like fire) and the rejection. So, although V1 is the decision speed for the pilots, the calculations behind it assume that the actual event happened at a slightly lower speed and that the pilots only got the chance to react by V1. In other words, the normal delay you expect from a normal pilot who's not expecting an event is built into the V1 calculation

IIRC, the delay is 2 or 3 seconds. But the RTO tests are in a controlled environment, where actual line ops is not. The RTO tests have much more control of external factors that line operations do. The NTSB was, and still is very critical of the current V1 certification. However, they don't recommend an alternative.

Some airlines I have been involved with use wet V1 speeds all the time. That provides for a much more conservative approach to the V1 issue and is more "GO" focused.

Quoting tdscanuck (Reply 22):
Optional on Boeing, standard on Airbus.

Granted it's optional on the Boeing but could you elaborate on the Airbus? SRS provides the engine out speeds V2 or higher if you have that and a minimum of 120FPM climb. So, I am somewhat stumped as to what you are trying to point out.
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26point2
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RE: V1 - A Danger?

Thu Oct 28, 2010 2:58 pm

I recall learning during my initial RTO training in the 90s that a high speed abort is 10 times more likely to result in a crash rather than continuing the take-off.

I think of this during every takeoff and mumble to myself before V1 "stopping stopping stopping stopping....". At V1 I mumble "going" and let go of the TLs. Kinda goofy has worked for me for 20+ years..
 
DH106
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RE: V1 - A Danger?

Thu Oct 28, 2010 3:03 pm

Quoting Vmcavmcg (Reply 24):
Quoting DH106 (Reply 20):
AA191 at Chicago, 1979?

I think you might want to re-read the accident report. There is no mention of rejecting above V1. The accident led to the V2+10 concept rather than taking your airspeed and if you are above V2 using pitch to achieve V2.

Granted, but you asked for an example of an accident where the outcome would have been less severe had the TO been rejected after V1. The engine seperation occured at rotation and a rejection at this point would certainly have saved at least 2 lives (the 2 killed on the ground). I conceed that in the real world the pilots didn't have the time nor the means to distinguish this from a 'standard' engine failure and thus flew the set procedures.
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Vmcavmcg
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RE: V1 - A Danger?

Thu Oct 28, 2010 3:53 pm

Quoting DH106 (Reply 26):
Granted, but you asked for an example of an accident where the outcome would have been less severe had the TO been rejected after V1.

And this is your opinion? Sorry, but I disagree. Had the crew kept the speed they had rather than trading it for altitude as was the procedure then, the results would have been different.

Having only flown Boeing and Airbus aircraft, I would be inclined to agree with them. Their reject philosophy is identical. The aircraft has a much better chance when taken into the air. Aircraft aren't made for off roading!
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DH106
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RE: V1 - A Danger?

Thu Oct 28, 2010 4:37 pm

Quoting Vmcavmcg (Reply 27):
Quoting DH106 (Reply 26):
Granted, but you asked for an example of an accident where the outcome would have been less severe had the TO been rejected after V1.

And this is your opinion? Sorry, but I disagree. Had the crew kept the speed they had rather than trading it for altitude as was the procedure then, the results would have been different.

You're confusing the primary cause of this accident with the current thrust of the V1/abort arguement we're having.
I agree that the primary cause of the accident was that the aircraft became uncontrollable after the crew bled the excess speed above V2 off as a trade for height. However you asked for (and the current discusion concerns) accidents where the outcome could have been better had a crew aborted above V1 instead of continuing a TO. By that narrow criteria AA191 is surely a candidate.
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Vmcavmcg
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RE: V1 - A Danger?

Thu Oct 28, 2010 5:23 pm

Quoting DH106 (Reply 28):
By that narrow criteria AA191 is surely a candidate.

I disagree. They were we above Vr when the engine departed. The runway available for them to stop within the confines of the airport was insufficient. Now we add in the complete loss of the #1 Hydraulic system. There is no way rejecting the takeoff would have been an option. In addition, the crew did not know the engine had departed the pylon.

Quoting DH106 (Reply 28):
You're confusing the primary cause of this accident

I am not. Had the current engine out procedures been used then, the crew would have had a chance. But, the cause is not an issue. Your statement about rejecting the takeoff V1 and Vr is just absurd.

As PiHero stated, this argument had been on this forum many times. The people who argue the most about why it's a good idea are the people who are not in the industry. YOU DO NOT REJECT ABOVE V1!!!!!!
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aerologan
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RE: V1 - A Danger?

Thu Oct 28, 2010 6:55 pm

Quoting tdscanuck (Reply 22):
Quoting Vmcavmcg (Reply 13):
The V1 speeds are based on new brakes, new tires a known runway surface (flight test) and flight test pilots.

That's not actually true...braking performance testing is done on partially worn brakes, and the worst case (MTOW RTO at V1) has to be done with fully worn brakes. With carbon brakes, the stopping performance doesn't change much with wear anyway, just the heat capacity.


  

From FARs
Sec. 25.101
(3) Include allowance for any time delays, in the execution of the procedures, that may reasonably be expected in service.
[(i) The accelerate-stop and landing distances prescribed in Secs. 25.109 and 25.125, respectively, must be determined with all the airplane wheel brake assemblies at the fully worn limit of their allowable wear range.]


but also keep in mind that from FAR 25.109
(f) The effects of available reverse thrust--
(1) Shall not be included as an additional means of deceleration when determining the accelerate-stop distance on a dry runway;

So if the failure is not an engine failure and max reverse is available and you have nice new shiny tires and brand new brakes, it could be said that there are occasions where an airplane could come to a complete stop after V1.

But as others have said, the V1 speed is there for a reason. Because statistically it is safer to take off.
 
DH106
Posts: 644
Joined: Wed Jun 15, 2005 5:32 pm

RE: V1 - A Danger?

Thu Oct 28, 2010 7:08 pm

Quoting Vmcavmcg (Reply 29):
Quoting DH106 (Reply 28):
By that narrow criteria AA191 is surely a candidate.

I disagree. They were we above Vr when the engine departed. The runway available for them to stop within the confines of the airport was insufficient. Now we add in the complete loss of the #1 Hydraulic system. There is no way rejecting the takeoff would have been an option. In addition, the crew did not know the engine had departed the pylon.

Nevertheless, HAD they rejected at Vr then at the very minimum, 2 lives would have been saved.

Quoting Vmcavmcg (Reply 29):
Quoting DH106 (Reply 28):
You're confusing the primary cause of this accident

I am not. Had the current engine out procedures been used then, the crew would have had a chance. But, the cause is not an issue. Your statement about rejecting the takeoff V1 and Vr is just absurd.

I'm not arguing with you about the cause of the accident. You asked for an example where HAD the crew aborted, the outcome would have been 'better'. Since the area beyond R33R was pretty sterile that had to be a better outcome than killing people on the ground as did happen.

Quoting Vmcavmcg (Reply 29):
As PiHero stated, this argument had been on this forum many times. The people who argue the most about why it's a good idea are the people who are not in the industry. YOU DO NOT REJECT ABOVE V1!!!!!!

Once and for all - I'm am not arguing with the princple you state above, merely supplyingy an example for which you challenged.
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: V1 - A Danger?

Thu Oct 28, 2010 7:32 pm

Quoting tdscanuck (Reply 22):
However, most flight crews don't have the data to hand in a line environment to quickly figure out which situation you're in, and an engine failure near V1 is no time to be trying to remember if V1 was moved to match Vr or not.

You're quite wrong. Through the use of our RTOW tables during our takeoff preparation, we know exactly where we are in terms of performance, what kind of limitation we're facing, and by how much...That done, we respect those values and the procedure.

Quoting tdscanuck (Reply 22):
The flip maneuver (raising Vr to equal V1, or at least raising it some amount above the strictly required speed to fly out at the normal V2) is an improved climb takeoff...using more runway to gain more speed.

Probably a typo but you can't "raise your Vr to match your V1 but rather the opposite, as Vr is fixed and depends on the aircraft weight, as both FAR and JAR agree :
"JAR 25.107 Subpart B / FAR 25.107 Subpart B
VR is the speed at which the pilot initiates the rotation, at the appropriate rate of about
3° per second.
(e) VR, in terms of calibrated air speed, […] may not be less than:
• V1,
• 105% of VMCA
• The speed that allows reaching V2 before reaching a height of 35 ft above
the take-off surface, or
• A speed that, if the aeroplane is rotated at its maximum practicable rate,
will result in a [satisfactory] VLOF”
"
In fact, our performances are computed with a V1 range such as .84Quoting tdscanuck (Reply 22):
Optional on Boeing, standard on Airbus.

So... What does that imply ?

Quoting DH106 (Reply 26):
but you asked for an example of an accident where the outcome would have been less severe had the TO been rejected after V1. The engine separation occured at rotation and a rejection at this point would certainly have saved at least 2 lives (the 2 killed on the ground).

I think you're freely playing with a tragedy : Going back to the report would tell you that the event occurred, as you said "during rotation", but what you omit to say was that rotation was done very slowly, that they achieved lift-off at V2 + 6 kt = 159 kt (hey, that's just 20 kt past V1 !!!) and some 6000 ft + down the runway... If you think that you could have stopped that 'Ten without a problem on the remaining available runway, then that's fine, and you're the man.
Or are you really ?
Contrail designer
 
lowrider
Posts: 2542
Joined: Wed Jun 30, 2004 3:09 am

RE: V1 - A Danger?

Thu Oct 28, 2010 8:07 pm

Quoting DH106 (Reply 31):
Nevertheless, HAD they rejected at Vr then at the very minimum, 2 lives would have been saved.

Or they could have risked killing all on board. I don't really see that as a desirable outcome. It would take some pretty sophisticated computer modeling to even begin to approach informed conjecture.

Quoting DH106 (Reply 31):
Since the area beyond R33R was pretty sterile that had to be a better outcome than killing people on the ground as did happen.

Look at the Kalitta overrun in Brussels. That was a fairly sterile overrun area too. Heavy aircraft make very poor off road vehicles. This has been proven many times over.
Proud OOTSK member
 
DH106
Posts: 644
Joined: Wed Jun 15, 2005 5:32 pm

RE: V1 - A Danger?

Thu Oct 28, 2010 8:22 pm

Quoting Pihero (Reply 32):
I think you're freely playing with a tragedy

Yes, you're quite right Pihero, I was getting too involved in reacting to Vmcavmcg's beligerance.
Your opinion I can respect.

Quoting Pihero (Reply 32):
If you think that you could have stopped that 'Ten without a problem on the remaining available runway, then that's fine, and you're the man.
Or are you really ?

I never meant to imply the 'Ten could be stopped, only pointed out that at least 2 lives at the bare minimum could have been saved thus achieving the 'better outcome' challenged for by Vmcavmcg.
I'm not the man, I never am.
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
Vmcavmcg
Posts: 78
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RE: V1 - A Danger?

Thu Oct 28, 2010 8:55 pm

Quoting DH106 (Reply 34):
Yes, you're quite right Pihero, I was getting too involved in reacting to Vmcavmcg's beligerance

????? Could you provide an example and I will remove it.

Quoting DH106 (Reply 31):
Once and for all - I'm am not arguing with the princple you state above, merely supplyingy an example for which you challenged

It is not only me that has challenged your example, but everyother professional pilot on this forum!

I think you are taking way too many liberties with this issue and you really need to read the NTSB report. There is not one hint about the crew rejecting the takeoff at Vr+ as you suggest. I can assure you, if the crew had attempted to reject as you suggest, the results would have been the same. The aircraft would have ended up in the same spot. IIRC, the DC-10 engine separated at right around the 6900' mark. That left 3100' remaining to stop within the confines of the runway. It is just not going to happen. Given the hydraulic issues and the unprepared surface, my guess is the DC-10 would have ended up in the same place.

Again, I think your example is not a very good one.
If we weren't all crazy, we would go insane!
 
DH106
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RE: V1 - A Danger?

Thu Oct 28, 2010 9:17 pm

Quoting Vmcavmcg (Reply 35):
I think you are taking way too many liberties with this issue and you really need to read the NTSB report

You're still missing the point I'm trying to make.
I make NO assumptions or predictions as to the outcome of the situation with regard to the DC-10. Almost certainly it would have overran, and perhaps become a fireball. I make no claim that it was a 'viable' reject in terms of the aircraft's safety.

However, in the accident as it actually happened, the aircrat impacted nearly a MILE (4600') to the NW of the runway and over a 1000' to the left of the extended centerline, an area which unfortunately contained a trailer park and it killed 2 people on the ground. Since the immediate runway overrun area was pretty much sterile I was merely making the point that these 2 people would have escaped and thus the outcome, in terms of fatalities, would have been better.
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
tdscanuck
Posts: 8573
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RE: V1 - A Danger?

Fri Oct 29, 2010 2:27 am

Quoting Vmcavmcg (Reply 24):
Quoting tdscanuck (Reply 22):
Optional on Boeing, standard on Airbus.

Granted it's optional on the Boeing but could you elaborate on the Airbus? SRS provides the engine out speeds V2 or higher if you have that and a minimum of 120FPM climb. So, I am somewhat stumped as to what you are trying to point out.

When you fire up Boeing performance software it will default to Improved Climb = None...it will calculate balanced field V1/Vr/V2 unless you tell it not to. Airbus (I was told by a performance instructor) is the other way...by default it will do an unbalanced-field calculation (equivalent to Improved Climb ON for Boeing), and you have to flip it back to do a balanced-field. It's nothing to do with SRS.

Quoting Pihero (Reply 32):
Quoting tdscanuck (Reply 22):
However, most flight crews don't have the data to hand in a line environment to quickly figure out which situation you're in, and an engine failure near V1 is no time to be trying to remember if V1 was moved to match Vr or not.

You're quite wrong. Through the use of our RTOW tables during our takeoff preparation, we know exactly where we are in terms of performance, what kind of limitation we're facing, and by how much...That done, we respect those values and the procedure.

There are a lot of airlines where takeoff performance data is provided by dispatch, or via an EFB. In those cases, if V1=Vr, there's no convenient way to tell if that's just where they fell out or if one of them was pulled up or down to match the other. The only way to tell is to run the tables yourself...some pilots, like you, do so, but many don't. Hence "most flight crews."

Quoting Pihero (Reply 32):
Probably a typo but you can't "raise your Vr to match your V1 but rather the opposite, as Vr is fixed and depends on the aircraft weight, as both FAR and JAR agree :

Yes, you can. The FAR/JAR definition is the *minimum* Vr. There's nothing wrong with raising Vr when you're on a longer runway to improve initial climb performance. It's done frequently in service.

Quoting Pihero (Reply 32):
JAR 25.107 Subpart B / FAR 25.107 Subpart B

That part defines the lower floor for Vr...as long as you have a runway long enough to have V1 get high, you're perfectly welcome to have Vr be higher than the minimum (up to tire speed limit, usually).

Tom.
 
Vmcavmcg
Posts: 78
Joined: Wed Sep 15, 2010 11:52 am

RE: V1 - A Danger?

Fri Oct 29, 2010 6:10 am

Quoting tdscanuck (Reply 37):
When you fire up Boeing performance software it will default to Improved Climb = None...it will calculate balanced field V1/Vr/V2 unless you tell it not to. Airbus (I was told by a performance instructor) is the other way...by default it will do an unbalanced-field calculation (equivalent to Improved Climb ON for Boeing), and you have to flip it back to do a balanced-field. It's nothing to do with SRS

Please re-read my question. I am well aware of what the OPS will do for Boeing, but I think you are confused on what it will do with Airbus. So, if you could elaborate on your statement with respect to Airbus that would help clarify things.

Quoting DH106 (Reply 36):
You're still missing the point I'm trying to make.

However, in the accident as it actually happened, the aircrat impacted nearly a MILE (4600') to the NW of the runway and over a 1000' to the left of the extended centerline, an area which unfortunately contained a trailer park and it killed 2 people on the ground. Since the immediate runway overrun area was pretty much sterile I was merely making the point that these 2 people would have escaped and thus the outcome, in terms of fatalities, would have been better.

Believe me, I am not missing your point! The simple fact is from the point of the engine departhing the wing to the end of the runway was just over 3000', add the overrun and you have another 1000'. The point of impact was 4000' beyond the end of the runway. So, at best we have 8000' to de rotate, and start to slow the aircraft down. Your position is it would have been more prudent to do that and risk the results of becoming an off road vechicle. I disagree, aircraft OEM disagree, saftey experts disagree. I guess we're all wrong!
If we weren't all crazy, we would go insane!
 
HaveBlue
Posts: 2176
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RE: V1 - A Danger?

Fri Oct 29, 2010 6:48 am

One thing I'd like DH106 to answer is that when that DC-10 lost its engine, and had to make a decision on what to do, do you think the crew knew that there were no lives on the ground to be lost if it did an aborted take off? That's ludicrous. The rules are the rules based on what is the best decision to make at that moment. In hindsight and armchairing you know that it was a 'sterile' environment beyond the runway, and that 2 died from them taking off. But you have a split second to make a decision on what to do with the aircraft, with unknown problems, bases on FACTS and TRAINING. There's airports where a runway overrun of any significant length will result in much more than 2 deaths... do you really think that is what's going thru the pilots head? The V1 decision speed is a sound one, and one born out of many tragedies and experience.

The simple response to the '2 lives lost could have been avoided' to me is that if that DC-10 had hit eslewhere there would have been no on the ground deaths at all, and it would be a moot point. And if a DC-10 had overrun the runway by 1,000' in a rejected take off just off the top of my head that would have caused MANY fatalities at Ft. Lauderdale Int going west, Daytona going east or west or north, and Orlando going north possibly... just as a few examples. Or Miami on the diagonal SE takeoff.

No one rule is perfect, but if it usually is the right decision, it got there for a reason.
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: V1 - A Danger?

Fri Oct 29, 2010 10:27 am

Quoting Pihero (Reply 32):
In fact, our performances are computed with a V1 range such as .84

for some reason, the rest of the quote has been lost during the posting :
This should have read thus :
..."our performances are computed with a V1 range such as Vr / V1 is greater (or equal to...) than .84 and Vr / V1 is lower (or equal to...) than 1 .Vr, on its own is very much defined by the requirement that , accelerating on N-1 engines, the aircraft would reach its screen height at V2. Therefore, Vr is pretty much dependent on the aircraft weight.
For us, operators, there is sufficient grounds for improved performance when , already we have chosen :
- a V1 range, as above, and...
- a V2 range, defined also as a ratio of V2 / Vs where the minimum V2 is 1.2 Vs or 1.13 Vs1g for the FBW 'buses, and the maximum when the aerodynamic max climb gradient is reached.
So I wonder where you found this :

Quoting tdscanuck (Reply 37):
The FAR/JAR definition is the *minimum* Vr. There's nothing wrong with raising Vr when you're on a longer runway to improve initial climb performance. It's done frequently in service.
Quoting tdscanuck (Reply 37):
hat part defines the lower floor for Vr...as long as you have a runway long enough to have V1 get high, you're perfectly welcome to have Vr be higher than the minimum (up to tire speed limit, usually).
Quoting tdscanuck (Reply 37):
Airbus (I was told by a performance instructor) is the other way...by default it will do an unbalanced-field calculation (equivalent to Improved Climb ON for Boeing), and you have to flip it back to do a balanced-field. It's nothing to do with SRS.

It really galls me that people haven't still accepted any of the Airbus methods and still think that the ole Boeing way is better. And no, that A perf is ceratinly not equivalent to an improved climb, that's a very limited view on the whole subject : Why in Hell would I force the Airbus perf program to compute the greatest fallacy of our modern aviation, i.e the balanced field performance ?
That balanced field exists, yes, but in some really, really extreme cases of short / high / hot airfields.
Otherwise, on a 12,000 ft runway, V1 is still defined for B at the ASD/TOD graphs intersection, even if that intersection happens at 4500 ft...
The Airbus programs (and I might add that on this case AI was THE pioneers as a computerised performance was already in service for the A-300 and A-310 in the mid-1980s ) gives you the best performance achievable on the actual conditions ( Max weight or max derate ) and reverting to a "balanced perf " instead of "balanced field " is totally pointless because, if it were the case, on a limited runway, the program would take the exact "balanced field performance".
Contrail designer
 
User avatar
glen
Posts: 358
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RE: V1 - A Danger?

Fri Oct 29, 2010 12:39 pm

Quoting Pihero (Reply 40):

  

In the following document we find a detailed explanation of how TOW-calculation is done on Airbus (Appendix 2)
http://www.smartcockpit.com/pdf/flightops/aerodynamics/18


Regarding the initial discussion about the danger of abortion beyond V1, the following graph might be interesting (balanced take-off):


Look at the overrun speed with only a few knots above V1 at abortion!

[Edited 2010-10-29 05:42:46]
"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
 
tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

RE: V1 - A Danger?

Fri Oct 29, 2010 5:16 pm

Quoting Vmcavmcg (Reply 38):
Please re-read my question. I am well aware of what the OPS will do for Boeing, but I think you are confused on what it will do with Airbus. So, if you could elaborate on your statement with respect to Airbus that would help clarify things.

You said it yourself:

Quoting Pihero (Reply 40):
The Airbus programs (and I might add that on this case AI was THE pioneers as a computerised performance was already in service for the A-300 and A-310 in the mid-1980s ) gives you the best performance achievable on the actual conditions

Airbus will always go to best performance achievable for the conditions, Boeing (by default) will go for balanced field length. Either one can do it the other way, they just choose different defaults.

Quoting Pihero (Reply 40):
It really galls me that people haven't still accepted any of the Airbus methods and still think that the ole Boeing way is better

I'm not sure how you got that out of any of my posts...I was just pointing out that they do it differently, as we both seem to agree.

Tom.
 
Vmcavmcg
Posts: 78
Joined: Wed Sep 15, 2010 11:52 am

RE: V1 - A Danger?

Fri Oct 29, 2010 5:34 pm

Quoting tdscanuck (Reply 37):
When you fire up Boeing performance software it will default to Improved Climb = None...it will calculate balanced field V1/Vr/V2 unless you tell it not to. Airbus (I was told by a performance instructor) is the other way...
Quoting tdscanuck (Reply 42):
You said it yourself:

My point was your statement was incorrect. Boeing and Airbus take a very different approach to TO performance. However, I flew for a SE Asia carrier that did not use improved take off numbers, they were available but the "normal" performance was our standard.
If we weren't all crazy, we would go insane!
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: V1 - A Danger?

Fri Oct 29, 2010 5:38 pm

Quoting tdscanuck (Reply 42):
Airbus will always go to best performance achievable for the conditions, Boeing (by default) will go for balanced field length. Either one can do it the other way, they just choose different defaults.

So, if I understand you well, :
-Airbus goes for the best performance achieved for the conditions as a default
- Boeing is satisfied that the balanced V1 perf is valid for most cases, that's why it's taken as default, right ?
You could understand that it's a lot different from :

Quoting tdscanuck (Reply 37):
Airbus (I was told by a performance instructor) is the other way...by default it will do an unbalanced-field calculation (equivalent to Improved Climb ON for Boeing), and you have to flip it back to do a balanced-field. It's nothing to do with SRS....

...which is wrong as we never revert to the balanced V1 calc (a bloody waste of precious time, especially when the codes for the limitations are well apparent, which was why I wrote that at all times in my takeoff prep I knew where I stood in terms of performance.).
Contrail designer
 
tdscanuck
Posts: 8573
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RE: V1 - A Danger?

Sat Oct 30, 2010 1:48 am

Quoting Vmcavmcg (Reply 43):
My point was your statement was incorrect. Boeing and Airbus take a very different approach to TO performance.

That was my point...I'm not sure which part you're claiming was incorrect.

Quoting Pihero (Reply 44):
So, if I understand you well, :
-Airbus goes for the best performance achieved for the conditions as a default
- Boeing is satisfied that the balanced V1 perf is valid for most cases, that's why it's taken as default, right ?

Exactly.

Quoting Pihero (Reply 44):
You could understand that it's a lot different from :

This might be a translation problem...to my eye, those two statements meant the same thing. At least, I intended them to.

Quoting Pihero (Reply 44):
...which is wrong as we never revert to the balanced V1 calc (a bloody waste of precious time, especially when the codes for the limitations are well apparent, which was why I wrote that at all times in my takeoff prep I knew where I stood in terms of performance.).

I didn't mean to suggest that you'd actually take the improved climb numbers and back out the balanced-field...I agree, that would be a "bloody waste of precious time". I just meant that the default position of A & B are mirrors...you can get either improved climb or balanced field for other aircraft, but they start in the opposite spots.

Tom.
 
thegeek
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RE: V1 - A Danger?

Sat Oct 30, 2010 2:34 am

Is anyone suggesting that the pilots of AA191 had a reasonable reason to reject the takeoff after V1, even if they had known the full extent of the damage to the plane?

The Concorde crash may have been different. But it may not have been. Most on board fires which reach the media result in no survivors, unfortunately. The FR 738 is the only exception I can think of.
 
Gingersnap
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RE: V1 - A Danger?

Sun Oct 31, 2010 5:32 pm

Slightly off topic (didn't see this in here but I could be wrong):

But say an aircraft had an extremely low V1 speed due to a light load (or a positioning flight). Would the V1 speed be misleading in terms of "you must take off from here on". On a long runway, wouldn't the crew be able to stop the aircraft on the runway from well in excess of the V1 speed?

I'm not saying it should be attempted or even thought about...but would it be possible?
Flown on: A306 A319/20/21 A332 B732/3/4/5/7/8 B742/4 B752 B762/3 B772/W B788 C152 E195 F70/100 MD-82 Q400
 
CosmicCruiser
Posts: 2477
Joined: Tue Feb 22, 2005 3:01 am

RE: V1 - A Danger?

Sun Oct 31, 2010 5:38 pm

Quoting GingerSnap (Reply 47):
But say an aircraft had an extremely low V1 speed due to a light load

Generally from what I always see under those circumstances V1 = Vr. There would be no reason to have a low V1. I've been very light taking off at CDG for FRA and V1 & Vr = 135kts.
 
tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

RE: V1 - A Danger?

Sun Oct 31, 2010 8:10 pm

Quoting GingerSnap (Reply 47):
But say an aircraft had an extremely low V1 speed due to a light load (or a positioning flight). Would the V1 speed be misleading in terms of "you must take off from here on".

Light weight means you can accelerate and stop quickly...that should lead to a high V1, purely from a performance perspective, not a low V1.

Light weight leads to a low Vr, and since V1 can't be higher than V1, you end up having to pull V1 down:

Quoting CosmicCruiser (Reply 48):
Generally from what I always see under those circumstances V1 = Vr. There would be no reason to have a low V1. I've been very light taking off at CDG for FRA and V1 & Vr = 135kts.

Tom.

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