Originally Posted by
LeadSled
Folks,
All I can say is most of you are obviously talking about matters of which you have no relevant knowledge. That is, takeoff performance calculations and accountability, and the used of reduced thrust takeoffs.
That the aircraft becomes airborne close to the end of the pavement signified nothing.
The Antonov at Canberra is nothing exceptional.
The video that is your "primary evidence" shows nothing exceptional, and it looks like a very well controlled rotation and initial climb, to me. The initial rotate attitude may have been a little low, based on the slight increase toward the end of what appears to be clearway. Without a runway survey, I cannot assess the runway plus stopway plus clearway, so I have no way of judging where the screen height should have been achieved in the video.
Tootle pip!!
LEAD, Absolute rubbish, and dangerously so.
Aircraft performance for takeoff is part of the PSCP certification process for the approval of the TC. The aircraft must (not maybe, MUST) comply with it's Type Certificate, and also be in a safe condition on order to be deemed AIRWORTHY.
When you derate a takeoff, you are effectively making a performance case for a higher temperature environment than you actually have. That permits a reduction in thrust setting and saves on engine wear from high rotor speeds and EGT's. Turbine wear is highly non linear as it approaches higher temperatures.
At ALL not just when you think it might be nice to, you are required to meet the requirements laid out in the certification 14CFR PART25/CS25 which are repeated in the local regulations under appropriate sections such as CAO 20.7.1.B.
FYI, and note the reality check on this:
YOU must comply with the most limiting case of either the all engines case, which is factored, or the engine out case. Both have screen heights that must be attained. We usually (and very luckily so) get to see the all engine cases. That is great. For the all engines, there is a 115% margin applied to the outcome, so pretty much the aircraft is required to achieve the screen height of 35' at 100/115 or 87% of the TODA. (OK, 86.96%). So on a 11500' long runway, any aircraft is absolutely required to achieve the 35' screen height without a failure at 10,000' down the runway. If it doesn't, and there is no specific cause of the perofrmance failure, e.g., crew setting wrong power, wrong data/temp, wind change etc, then it is NOT AIRWORTHY. An aircraft that is at 35' and operating at V2+10 or thereabouts, in the second segment has a minimum gradient that it must achieve dependent on the number of noise makers, but it is also in a steady state condition more or less, so it is relatively easy to ascertain what the additional height should be when the aircraft passes the fence (TODA). A heavy jet on all engines will achieve a couple of thousand FPM on all engines at V2+xx, or about 10m/sec, or 33', whatever... it will also be doing some where between 140-180KIAS which is more or less also TAS. In still air, that is ground speed more or less, and yes you can work it out from the info that is historically recorded for the airports. 1 Knot = 1.68781 Feet per second. 140Kts is 236FPS, 180 is 303... At the higher speed, it takes 5 seconds to pass 1500', after the screen height. in that time the plane will climb 5x33 =165 feet higher than the screen height, which is now a height of 200', at the end of TODA. That is without an engine failure.
If you are at 35' at the end of the TODA on all engines, you would be DEAD if you have an engine failure anytime around V1 through to liftoff, and possibly later as well, dependent on the causal factor.
That holds true for DERATED or FULL THRUST cases, the only difference is a trade off towards the limit case as indicated above every time you derate.
Take the same runway, and look at the speeds for rotate, and consider when Vr MUST occur in order to be legal. This is simple DF maths, nothing special.. The aircraft achieves a Vr of say 170 for the V2 case of 180, some distance before the screen position. The plane has to alter its attitude, generate lift and continues to accelerate until achieving a stable target speed. For simplicity, take the average speed (plane is required to achieve V2 by 35' as well in the OEI case). So the mean speed is 175KIAS, 295FPS. How long does it take to rotate, achieve the attitude and get to 35'. Good question. The FCTM or FCOM will provide that guidance, as does the data of all the takeoffs that get done. And it happens to be about 5 to 6 seconds for the wheels to be off the ground, and about another 2-2.5 seconds to achieve 35', being generous. So using the shortest possible figures, you have 5+2= 7 seconds at 295FPS=2065' from "ROTATE!" to getting to 35'. It could also be as much as 2500'. What is ain't is instantaneous, we don't levitate, we rotate. So now on the 11,500' runway we get to be at rotate at 10,000-2,000 to 10,000-2,500 = 8,000' to 7,500' down the runway.
On an instrument runway, assuming there is no clearway of interest, then there are touchdown zone markings in the last 3,000' of each end of the runway, so you get to see the departure end stuff under your nose (vertically below, not visual cutoff) at 8.500' down the runway.
IF YOUR RUNWAY DOESN'T INCLUDE STOPWAY, on a limit takeoff on the assumed 11,500' runway, you get to rotate well before approaching the 3000' markers. By well before, enough that if you have already lost sight of the first marking, you have a compromised takeoff performance case.
For any one interested, go and stand across from that exact point, (use Google Earth... check where it is, use the Jepp or declared distances to ascertain the applicability of CWY etc to the TODA... but you can go and look at that point and see if the nose of the aircraft commences to rise anywhere near that.
Alternatively, you can just watch the aircraft pass the TODA distance, and look at the relative height above ground reference using the wingspan, tail height, wheel diameter, door heights etc as gnomons. Sometimes you don't need to do that, as there is no vertical distance to be discussed. I did this once for an A340-300 taking off on 07R at VHHH, and the measuring yard stick was the Toyota taxi that it was no higher than the roof height above the Toyota as it passed overhead. The main wheels came off the ground within 500' of the end of the runway. The windsock showed a headwind throughout, and it agreed with the ATIS at that time. (Nothing against the A340, but it does love runway, but it is not even close to being alone in that regard).
We have engine failures at the worst position very rarely, as in almost never. The legal case remains the legal case, and if your plane is not making the numbers, then that is a mandatory reportable event. Read your airlaw.
Do/Don't as you see fit. But as an operator, normalisation of deviation doesn't make the world safer, and certainly doesn't make the problem go away.
The causes of failure are various, and sometimes they are not within the purview of the crew, they may be much deeper than that. As a pilot, don't believe that you have lots of additional padding to waste on runway line up and similar, or that there is additional reserves for messing about, there is not. I have been in seat 1A of a B744 that perfectly aligned with the centerline and I had the 1500' markers outside of my window, then we took off. That was a limit case takeoff, and we didn't get close to remaining legal on it. Does the FOQA system pick up such items?
NO.
Summary:- DERATED operations should never result in a lower screen height, the aircraft is still required to have met the performance of the assumed higher temperature. Don't confuse that with a wet V1 accepted reduction in screen height (reducing the wet V1 not below VMCG by a specified value improves the reliability of the rejected takeoff case, but results in the lower screen height being accepted. The lower screen height is not an acceptable height to achieve without a damn good reason, like having a wet runway, applying a reduced V1 and having a failure at Vef.).
- Getting to 35' on all engines at the end of the TODA and no more, proves conclusively that you did not have the ability on that takeoff to accept an engine failure, deal with that knowledge as you see fit.
- The only people identifying performance failures are the flight crew, and as a group we grossly fail to meet our moral obligations, but then, that makes us no worse than the rest of the system that doesn't give a damn either.
- It's your life, and those of your passengers, family and friends.
- A failure doesn't occur in the critical condition often, but they do on occasions (stuff happens to marines... ) but that doesn't make it right.
- Do not waste runway, the margins may be less than you think for reasons outside of your direct control, and some due to your own actions.