Hacker15e
Who am I? Where are my pants?
This makes a huge assumption that there's something about computing V1 based on ARL that means "operating hear the margins of aircraft capability", and there's really no reason to believe this is true.
Sad Realization
- Thread starter Finhunter89
- Start date
This makes a huge assumption that there's something about computing V1 based on ARL that means "operating hear the margins of aircraft capability", and there's really no reason to believe this is true.
PhilosopherPilot
Well-Known Member
What kind of data are you looking for dude?
Hacker15e
Who am I? Where are my pants?
Thanks, not my first rodeo.
If you think that sounds sporty, try doing them with 20,000 pounds of actual explosives -- bombs -- under the airplane and near those hot brakes.
Yes, I HAVE actually blown the plugs and had to sit there for 20-30 minutes while the fire department didn't want to advance any closer because of the heat and fire risk.
As I said before, there may be (rare) times when the plane is too sick to fly, and getting airborne will be guaranteed death, as opposed to an abort past V1 which may only be possible death. It's the difference between having 2-pairs, or 3 of a kind: both crappy hands overall, wih one only slightly better than the other.
Dugie8
Well-Known Member
It isn't just he blowing of the plugs it's the loss of braking ability. There are plenty of things I would rather run off the end of the runway for vice taking it into the air, cabin fire....
Those things are no win situations to begin with and now we are calculating runway requirements on conditions that have a very very low probability of occurring, thus limiting outer take off weight because now I can't abort above V1 without overrunning the runway or now my brakes are so heavy that I'm leaving payload behind anyway. If your method isn't weight limiting, there is no reason to calculate it, IMO.
The balanced field method gives me max weight at the shortest possible pavement required. I honestly don't see a better way to do it. Nevermind the can of worms contaminated runways would present.
Those things are no win situations to begin with and now we are calculating runway requirements on conditions that have a very very low probability of occurring, thus limiting outer take off weight because now I can't abort above V1 without overrunning the runway or now my brakes are so heavy that I'm leaving payload behind anyway. If your method isn't weight limiting, there is no reason to calculate it, IMO.
The balanced field method gives me max weight at the shortest possible pavement required. I honestly don't see a better way to do it. Nevermind the can of worms contaminated runways would present.
Hacker15e
Who am I? Where are my pants?
Something other than "it is safer" and "it is more conservative" without any actual knowledge to back up if it, in fact, is, and if so, then why.
What I'm seeing is 121 folks who have only operated using one procedure, believe in it with religious fervor, and believe that any suggestion of deviation from it is automatic heresy.
I have flown airplanes that compute TOLD both ways, and it makes more sense to me to have numbers that reflect actual conditions and capabilities. I'm trying to find an actual reason for why the FAA decided to go one way, while the military went another.
Hacker15e
Who am I? Where are my pants?
No.
By definition, V1 calculated based on actual runway length means you can stop in the remaining runway distance.
Sometimes, they destroy the whole aircraft too, even with the abort completed still on pavement.
Here:
http://forums.jetcareers.com/thread...ved-with-good-intentions.183089/#post-2154052
It's one of those "it depends" things. The procedures are set in stone for the most part, I agree. However there may be specific emergencies either catastrophic in nature, or aircraft situational, that may need to be briefed. The latter may not be for most airliners in use today, but the former very well could be.
As an example of a situational, in the F-117, we briefed and understood abort past V1, if encountering a dual generator failure on departure with solid IMC above that we wouldnt be able to reasonably remain below to enter closed pattern and land. Why? Because the airplane automatically reverted to battery only, and standby instruments. The battery was good for 30 minutes, so realistically about 15 or so minutes because it wasn't right out of the box and brand new. But 15 mins was hardly enough time to get radar vectors back to a landing, and once that battery died, the airplane was a flying brick, as the FBW failed too, that was only headed down to a smoking hole in the ground.
But for us, this was a standard. It was a known, and pretty much a procedure. Just like your procedures for your aircraft are your standards....briefed and known. My only point being, there are rare extenuating times when keeping a ground emergency a ground emergency, is the best course of action, rather than making it an air emergency and sealing your death. Airmanship is what comes to play here, as previously described a few pages back.
Dugie8
Well-Known Member
Right, but now you are going to be limiting your takeoff weight by moving V1 faster to make your stopping distance equal the runway length. Not to mention you have to move Vr and V2. You could have two speeds a normal V1 and a high speed abort speed, Vhs. Vhs would then have to be limiting and you would start taking off weight to meet the limit.
If one came at it another way and said for today your BFL is X at your current weight and your Vhs is Y where Y gave you a stopping distance equal to the runway length, you have something. But, I again would WAG that Vhs speed would not be very far from your current V1, simply because the brakes don't care how long the runway is.
He's got the whole collection.
jtrain609
Antisocial Monster
Correct. The CHQ -145 in JFK with the sheared elevator cables. That plane was never getting off the ground, and they just got lucky that the V1+20 abort happened on a long runway.
The problem is that we don't do a very good job of identifying those situations. I mean sometimes we can't even keep the plane tracking straight down the runway when nothing is broken.
There was NOTHING wrong with that aircraft, and they departed the side of the runway due to a crosswind (http://en.wikipedia.org/wiki/Continental_Airlines_Flight_1404).
Hacker15e
Who am I? Where are my pants?
If you go back to my original post on the subject, this is exactly what I said the military does as part of the TOLD computation.
PhilosopherPilot
Well-Known Member
Then you'll have to talk to the FAA. None of us know WHY they do it that way. A few posts back I guessed why, but that's a guess.
As far as data goes, we can talk generally, but no one is going to post on a public forum specific data about their airline. Luckily, you don't need data when you're comparing relative safety. Since safer = less risk, it's pretty easy to tell when things are relatively more safe even if you can't quantify exactly how much safer it is.
Boris Badenov
Fortis Leader
This much hand waving, there ought to be train pulling out of the station or a ball game on or something
jtrain609
Antisocial Monster
Hacker15e
Who am I? Where are my pants?
Pretty funny that's where we've ended up, since my original question asked why the FAA chose that. All of this was just a big irrelevant loop around the actual topic, unfortunately..
If "safer" and "less risk" is the concern, then why not compute V1 with an even bigger conservative buffer? Wouldn't that be safer-er?
This is circular logic, again. Safety is not job #1; if it were, nobody would crank an engine or turn a wheel. The actual job is to balance accomplishing the mission with safety, and that means there is inherent risk. That line has to be set at a place which allows the actual point of flying the airplane to be accomplished.
So, V1 isn't computed even more conservative because it reduces capability beyond what is reasonable risk (and could even cause some additional risk of its own).
I don't buy that calculating V1 on actual runway length increases risk beyond what is acceptable. Again, the military flies a LOT of airplanes for a LOT of cycles and has a commensurate number of emergencies. There's no demonstrable data in there that ARL-computed TOLD presents any unreasonable risk. Yes, high speed aborts and runway over-runs are bad stuff...and when V1 is computed for the actual runway it by definition allows the aircraft to safely stop in the remaining runway distance.
By the same token, I have never seen any data which factually argues that there is a necessary safety buffer over ARL-computed data by using BFL. If there is some, PLEASE post it! I'm completely interested if there is, and as an aviator I'm always open to changing my opinion in the presence of new information.
The FAA didn't just pull BFL out if its collective asses and choose not to compute it based on ARL...so why?
jtrain609
Antisocial Monster
PhilosopherPilot
Well-Known Member
I guess our point is compute the V1, and we will respect it. As long as the number is valid and safe, who cares? Frankly, our V1 and VR numbers are so close, there won't be more than 1 or 2 knots difference in your method and the BFL method in most circumstances. We call V1 5 knots prior to V1 at my airline. So we commit to going 5 prior... I'm not sure what difference it would make to calculate it differently, honestly.
Hacker15e
Who am I? Where are my pants?
Absolutely, no question about that.
Yes...which is why I am confused as to the hand-wringing, tooth-gnashing, and finger-pointing responses in this thread to my question.