Because math....
Many people on this board use the wrong "their/there/they're" - and others use "coz" instead of "because" - you expect them to be able to do simple math?!?!
Sad Realization
- Thread starter Finhunter89
- Start date
Because math....
Many people on this board use the wrong "their/there/they're" - and others use "coz" instead of "because" - you expect them to be able to do simple math?!?!
Boris Badenov
Fortis Leader
No no, they're experts Hacker. EXPERTS I TELL YOU!
Dugie8
Well-Known Member
It isn't the FAA it's the stopping ability of the brakes. Assuming a transport category airplane, you could very easily exceed the thermal capacity of the brakes with a reject beyond V1 even at weights below MGTOW.
F=MA
Balanced field gives you the shortest runway possible. Making brakes bigger, thus heavier would be useless for the very few operations that would allow for high speed rejects, ie very long runways.
Boris Badenov
Fortis Leader
There's a chart for that!
Dugie8
Well-Known Member
There a lot of charts for that!
Boris Badenov
Fortis Leader
Yeah, I mean, obviously must be considered. I think what hacker is getting at, though, is that it COULD be calculated. Particularly in this age of computers doing all the work. But noooooooo, because, you know, it's unsafe. For some reason.
Dugie8
Well-Known Member
Sure. To what benefit though? Unless bigger brakes are going to be the norm you wouldn't get any real benefit from calculating it. Plenty of evidence to support high speed aborts WHEN the airplane is airworthy are bad juju.
I shudder at the thought of aborting a Beechjet at 140 knots.
Hacker15e
Who am I? Where are my pants?
That's the point -- we're NOT talking about the "shortest runway possible". We're talking about LONG runways, where maximum effort braking is not required, even at higher speed aborts.
I have flown jets with ridiculously incapable braking systems (as in no antiskid) compared to the weights and speeds involved. It was never difficult to look at the brake energy chart as part of the TOLD review and know what the risks of a very high speed abort were in those terms. With very long runways, stopping technique was part of the discussion.
It would be VERY easy to have overlapping data which said "at abort speeds above XXX KIAS and XXXX gross weight, braking capability is significantly reduced".
IMHO, still not a good reason to not compute TOLD based on actual runway length.
Dugie8
Well-Known Member
Eh. Agree to disagree. Unless you have a proven procedure for braking technique that will not exceed the brakes capacity and allow you stop the aircraft on the available runway otherwise you just became a test pilot and they don't pay me enough to to do that.
PhilosopherPilot
Well-Known Member
It won't be unsafe if it were calculated. (Actually based on data.)
I think the pushback you are getting is coming from the concept of aborting past V1, however it is calculated, is a bad idea.
Hacker15e
Who am I? Where are my pants?
This is exactly the issue. If the inputs used to calculate V1 don't represent actual conditions, then the result doesn't represent actual capabilities of the aircraft.
The idea that, hypothetically speaking, you'd blindly adhere to a "balanced field" calculated V1 when you have, say 50,000' of runway in front of you is ludicrous.
I completely understand the habit of not aborting above V1 -- that's not what we're discussing here, though.
Bandit_Driver
Gold Member
Aborts above V1 make you a test pilot. If it works out great you get to be the hero for 5 minutes. It doesn't work out you are now out of job, out of a license, and leave your airline facing suits if people were hurt or killed. Boeing, Airbus etc will just point the finger at you along with your company, pointing out you didn't follow MFR, COMPANY, and FAA approved procedures.
Hacker15e
Who am I? Where are my pants?
Nothing to do with being a "test pilot". The military airplanes I've flown calculate TOLD this way, present the data this way, and aborts are executed using procedures to match. Nobody is inventing anything new.
My wonder, again, is why the FAA does not do this.
Bandit_Driver
Gold Member
If I don't have published numbers for it then I am a test pilot with regards to my plane. I would bet there are legal issues the FAA, Boeing, etc are trying to mitigate as much as possible..
jtrain609
Antisocial Monster
How long are your brief periods for a sortie?
EDIT: Let just me get to the point I'm trying to make, and I'll make an assumption regarding your brief.
My guess is that you guys have a much longer period of time to brief your flights than we do. We'll take a plane, and from blocking in to blocking out, turn it in under 30 minutes. That includes a post flight, getting the paperwork, making sure the paperwork is legal, programming the box, getting a clearance, blah blah blah. There are a lot of things to do in those 30 minutes.
To spend time determining how you're going to do the aborts, and then REMEMBER how you briefed you're going to do the aborts, is time we don't have. And frankly, it's brain power we likely don't have. To steal a line from George Carlin; think about how stupid the average pilot is, and then think that half of all pilots are stupider than that guy.
Our procedures are based on efficiency and safety. Safety comes from doing things the same way, ever time. So when the skipper says, "We'll abort for anything below 80 knots, and between 80 and V1, we'll abort for engine failure, fire, loss of directional control or an inability of the aircraft to fly, and above V1 we'll take the aircraft flying and treat any problems as an airborne emergency," you're on the exact same page. You've been trained for doing exactly that, and the skipper has briefed exactly that.
It's simple to the point that a caveman can do it, and we've proven over time that it's safe.
Is it max performance? No, but nothing we do is max performance. We derate our takeoff thrust so much on 90% of our takeoff's that we're dealing with a fraction of the thrust the engines can produce. We're not looking to employ our aircraft as a weapons platform, we're looking to employ our aircraft efficiently, and that requires some standardization.
Last edited:
PhilosopherPilot
Well-Known Member
I think the point you are missing is that for system safety the procedures built for an entire airline operation are geared towards acceptable risk, not the limit of the capability of the aircraft. This isn't the only example where the aircraft is more capable than our procedures allow.
My point is that if you have a V1 number, you as a pilot must respect it. If the airline changes how they calculate it, then you respect that new number. It is management's job to manage risk, and (one way) they do that through flight procedures. To insert self-assessment of risk by individual pilots introduces a ton of risk into the system, and removes the ability for management to control the level of risk to the level that they find acceptable.
So I'm this case, the current V1 number is more conservative. That's a good thing. Studies show that high speed rejects are hella dangerous. Rejecting past V1 is an excellent way to ball one up.
PhilosopherPilot
Well-Known Member
Hacker, I agree with you that if the number can be calculated differently then there's no harm in doing so, provided it's a valid number. My concern was the earlier posts seemingly condoning rejecting past V1, as if 121 guys are somehow lesser pilots for not doing so.
Hacker15e
Who am I? Where are my pants?
YBGSM. Really? It is no more brainpower than any other task we perform in flying airplanes which has more than one branch on the "if/then" tree (ergo, pretty much everything we do).
I think you guys who have not operated outside of the BFL-calculated V1 are way, way, way over-thinking this. It works exactly the same, just with some caveats at the corners of the performance envelope.
The "what if" example brief that you typed is pretty much exactly how it works in military jets, too. How we arrived at the numbers, and what the assumptions in those numbers are, are the only differences.
Manufactuers test aircraft this way, and publish data this way, because FAA Part 25 says that's what they have to do when producing a transport category aircraft.
So....we circle back to the beginning, my original question....why does the FAA not calculate refusal speeds based on actual ruway length?
The resultant number isn't any more "high performance" than the number based on BFL.
Yes, high-speed aborts can be dangerous. In just the same way that V1+1 engine failures can also be dangerous.