Air X 340 at Brasil...
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FDR lots of numbers and "facts" but DERATE and FLEX are TOTALLY different in the Airbus. Where on earth do you get this . Having flown various versions of the A340, hot heavy etc the end of the runway can be very close. V1 decision allows for 2 seconds not 1, and V1 is a long way behind the aircraft.
in in all areas of the world, well almost all... the AEO case is factored by 1.15 of actual. Therefore AOTBE, in the normal case you arrive at 35’ having flown 100%/115%, or... 87% of TODA. That’s AEO, there is no additional factor to OEI, your screen height is the end of TODA, 35’ unless the V1 was reduced due wet,, in which case the additional speed required to be gained engine out is accepted to give a 15’ screen height.
2 engine aircraft, you normally will not feel concerned with takeoff performance, doesn’t mean it is not critical, you are just normally on all engines. fort he 4 blowers, the margins of the AEO are interesting.
The take home is simple. 35’/15’ is a height across the weeds when you have had a failure 1 second prior to V1. In all other cases, you must obviously be better off. if you are not, or you are seeing say, 2’, 8’ 15’ 35’ at the end of the runway, then just as well you didn’t have a power loss, as it is a certainty you re compromised. how on earth do you egt higher with an engine out than with all engines at full puff?
FLEX/ etc is irrelevant. In all cases you must meet the screen height. JAROPS/EASA, CAAUK, CAANZ, casa, TC, CAAC, KCASA, JCAA, FAA etc. rules are the same. NK, maybe different...
Derate/flex is irrelevant. you must still achieve the same outcome, there is no free pass permitting taxiing over the. Golf course as your manual was written in Toulouse. Derate/ATM/Flex permit the assumption that the aircraft is operating in different conditions ie, smaller engines, (derated), or higher temperature (ATM/Flex), but in all cases, the actual weight must permit the operation, which retains the same criteria for the TO. Refer to Part 25 Subpart B, para 101 through 117, particularly 111 and first section of 113. CS25 same, and EU Ops etc follows suit. CASA CAO 20.7.1.B. says same in a more wordy manner. TC rule buried in their web rules.
To remove any question on there being a difference between a 'bus and a 'Boing,
CS25.113
Take-off distance and takeoff run (See AMC 25.113) (a) Take-off distance on a dry runway is the greater of – (1) The horizontal distance along the take-off path from the start of the take-off to the point at which the aeroplane is 11 m (35 ft) above the take-off surface, determined under CS 25.111 for a dry runway; or (2) 115 % of the horizontal distance along the take-off path, with all engines operating, from the start of the take-off to the point at which the aeroplane is 11 m (35 ft) above the take-off surface, as determined by a procedure consistent with CS 25.111. (See AMC 25.113(a)(2), (b)(2) and (c)(2)) ..... blah blah blah
excerpt from EU CS25 Amd 22.
§25.113 Takeoff distance and takeoff run.
(a) Takeoff distance on a dry runway is the greater of—
(1) The horizontal distance along the takeoff path from the start of the takeoff to the point at which the airplane is 35 feet above the takeoff surface, determined under §25.111 for a dry runway; or
(2) 115 percent of the horizontal distance along the takeoff path, with all engines operating, from the start of the takeoff to the point at which the airplane is 35 feet above the takeoff surface, as determined by a procedure consistent with §25.111.
(b) Takeoff distance on a wet runway is the greater of—
(1) The takeoff distance on a dry runway determined in accordance with paragraph (a) of this section; or
(2) The horizontal distance along the takeoff path from the start of the takeoff to the point at which the airplane is 15 feet above the takeoff surface, achieved in a manner consistent with the achievement of V2 before reaching 35 feet above the takeoff surface, determined under §25.111 for a wet runway.
(c) If the takeoff distance does not include a clearway, the takeoff run is equal to the takeoff distance. If the takeoff distance includes a clearway— blah blah blah.
Your bus is certified under CS25, which has exactly the same requirements as 14CFR Part 25 from the Kingdom of Trumpland.
Note, that at all times, once you get to the rough, you get 35' minimum clearance, + 48'/nm additive necessary, or 50' + + + in turns. If you are drooling off the end of the fairway into the rough, you have also compromised the 2nd segment in part.
Slow rotates are an issue, however, the maths is straightforward to ascertain the point on the runway at which Vr occurred, and thereby where the performance of the aircraft would achieve 35'. The discussion in no way suggests that there may not be sound reasons to use up lots of runway, but performance failures occur, recall the B747-200 out of Kai Tak on RWY 13... Use of overspeed is a fair thing, but that still is required to meet the screen height, Overspeed places the aircraft further tp the east on the drag polar, and thereby improves ROC for aircraft that are on the wrong side of the drag curve at V2 to V2 + 10/15 etc. The additional runway required to be used up in that however still must not encroach on the screen height, you gotta have spare concrete to do that, sufficient to permit a higher rotate speed than would normally be the case. The additional use of runway comes out where the OEM FCTM etc suggests using available runway for (presumably inadvertent) wind shear entry. Controllability around the rotate may justify using up some turf on delaying rotate until you are stable with a failure close to or at Vr, however any delay is potentially chewing into your screen height, so there needs to be good reasons.
Last edited by fdr; 8th May 2019 at 09:02.
I was on the A340-200 1992-1995 and recall about 55 s and about 3.000m take off run for a 12 hrs flight normal....
In these 3 years the T/O performance calc was revised three times.
Comparing 3rd to 1st it was a difference of 10 tons too optimistic by airbus
T/Os were in about ISA conditions e.g. SL, 15 deg, 1013 or very close.
In these 3 years the T/O performance calc was revised three times.
Comparing 3rd to 1st it was a difference of 10 tons too optimistic by airbus
T/Os were in about ISA conditions e.g. SL, 15 deg, 1013 or very close.
Last edited by gearlever; 8th May 2019 at 20:07.
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So AEO can be limiting because of the 15% margin requirement but in reality the plane will be higher/faster than in the OEI case. It is limiting regs wise but not actual performance.
I was on the A340-200 1992-1995 and recall about 55 s and about 3.000m take off run for a 12 hrs flight normal....
In these 3 years the T/O performance calc was revised three times.
Comparing 3rd to 1st it was a difference of 10 tons too optimistic by airbus
T/Os were in about ISA conditions e.g. SL, 15 deg, 1013 or very close.
In these 3 years the T/O performance calc was revised three times.
Comparing 3rd to 1st it was a difference of 10 tons too optimistic by airbus
T/Os were in about ISA conditions e.g. SL, 15 deg, 1013 or very close.
For a 4 engine aircraft, the AEO case is usually the limiting case that must be met, which is to attain 35' in 87% of the TODA (100%/115% x TODA) The OEI is still required to meet 35' in 100% of the TODA following a failure 1 sec prior to V1. The dots are as follows...
....
If on 4 engines you don't get to 35' at the end of TODA, then it is purely chance that you have survived, as you did not have an engine failure at V1. Doesn't matter if you are Chuck Yeager or Wonder Woman, if you don't have the energy, you are compromised.
Nothwithstanding comments to the contrary, the law applies equally to Boeings and Airbus, read CS25.111, 113 and FAR25.111, 113.
On 4 engines, you are required to achieve 35' at 87% of the TO roll, so consider, say, LHR/EGLL RWY7R 12,802' long. Disregard line up allowance... (required under 121, EU OPS1) ASDA = TORA, TODA is a bit longer, add 200' roughly. So the runway is 13,000' approximately.
For say a modestly heavy weight B744, representative V1 is around 155 (78m/sec), Vr 171(86m/sec) V2 181 (91m/sec). Target speed for the rotate is V2 +10, 191 (96m/sec). (These are not limiting weight speeds, the speeds can be higher).
Time from Vr to liftoff is in the FCTM. The QAR/DFDR data shows the crews generally achieve similar times from Vr to liftoff, a rotate to a slightly lower attitude will offset the difference in part by the additional speed, so the time to liftoff is about the same very roughly. A rapid rotate will lift off in less time, but the speed will be low. Generally for a Boeing, the plane will achieve V2 around the time the wheels tilt is recorded for a normal rotate, and achieve the target attitude at around 35' (RA measured needs to be adjusted for the attitude), and achieves around the V2+10 value (737, 757, 767, 777, 787 target speed is slightly higher, +15-25). at that point (on all burners).
Anyway, FCTM gives time from Vr to liftoff of around 6-6.5 seconds. over that time you continue to accelerate towards the climb out speed of V2+xx, which is then maintained. The TAS will increase slightly as you climb, and your ground speed will be changed by the gradient of wind with altitude. Neglecting all the trivial variables, 6-6.5 seconds at an average of between Vr and V2+say 10, (for a B74, is about 91m/sec), gives around 540m to 585m for the wheels to come off the ground.
The time to get the wheels to 35 is around 1.5-2 seconds, and is at a speed of V2+xx (say 96m.sec for the B74).
So, around 7.5-8.5 seconds after first commencement of rotate, the plane will achieve the desired screen height. that is going to be a total distance of... say 684m (2242'), (540+(96*1.5)), to 777m (2547') (585+(96*2)).
The screen height point on 4 is at 11,311' form the start of the runway. Deducting the distance from Vr to 35', that gives a point on the runway where Vr occurs at from 9069' to 8764' from the start of the TODA/ASDA/TORA. reduce this by your line up etc.
So there you are sitting in the front of the big jet at Vr. Looking out the side of the aircraft, you are about to pass the last of the landing zone markers for the reciprocal runway, RWY 09L, the 3,000' markers. (see image below). Looking out the front of your cockpit, you have already lost sight of the first marker, but only just, about 0.2 seconds for a B74, a little less for an A340, A380. (coaming cutoff angle/height, obscured area). This particular example has a displaced threshold in the reciprocal runway, so the markings are much closer to the beginning of the runway than they are normally without a displaced threshold on the reciprocal. That is notable, as this is the closest to the landing zone markers that you will see, all other normal limit takeoffs will have much more space between the markers and you when you get the "rotate" call at Vr. certainly is at vilacopas etc.
For the continued limit case takeoff, the aircraft is going to climb above 35' at the speed for 2nd segment, and at the IROC for steady gear up, flaps at takeoff setting, for the time remaining to cross the fence. For a fat B74, that is about 1,800FPM, or 30FPS. For this example that gives a further 5.3 seconds from the 87%TODA point to the end of TODA, which gives the screen height of 35' + 160' = 195' AGL at the end of TODA. (for 27R, the limit crossing of the displaced threshold of 09L would be around 80' AGL... ).
Doesn't matter whether your aircraft is A or B brand, or if you left or right handed, fluent in Swahili, English or Pidgin... CS25/FAR25 require this and that is for all aircraft, 4,3,2 etc. The closest that you will come to seeing the far end is invariably on the 4 engine case, the 3 and 2 engine cases are more constrained by the OEI case so appear to be better, but only appear to be, and they inherently mask any deficiency of the performance. It has been stated previously that the A340 performance was adjusted twice from initial issue, Boeing did the same with the B727 so it is not just a single manufacturer. It is a part of airworthiness that the aircraft comply with the TC, and a failure of takeoff performance is a failure to meet the certified performance, and means the aircraft is not airworthy, unless there is a non aircraft performance reason for the shortfall.
If you use flex/ATM or other method to reduce thrust the underlying performance requirement is that you must still clear the fence at the same point and by the same margins. The "15' wet" case is for the OEI case only, for a normal takeoff on a wet runway, there is no rejected takeoff using the lower V1, and there is no continued takeoff from V1 - 1 sec, so the aircraft in the normal takeoff does not achieve a lower screen height, and assuming that because you reduced V1 and didn't have an engine failure, that the fact you barely squeezed the old blender to 15' on all engines does not make you compliant, indeed, it assures that your survival was at risk.
The survival of the pilots is of passing concern, as a profession it is fair that the punters can assume that the pilots know enough about the requirements to know when there is a risk or not to the passengers safety, and to everyone that is in the path of the projectile.
It is quite straight forward to ascertain whether the aircraft was on all engines or not from external observation.
The acceleration of the aircraft on a normal takeoff is a 5th order polynomial, with a peak acceleration almost coincident with thrust set, and with a gently curving 2nd order curve from thrust set to Vr. From Vr, the curve is essentially 2nd order to a limit of 0 for the constant speed, neglecting the TAS change form 0' to 35'. For the 2nd segment climb out, the acceleration is linear for TAS, 0 for CAS.
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That is correct, however, the dots need to be joined.
For a 4 engine aircraft, the AEO case is usually the limiting case that must be met, which is to attain 35' in 87% of the TODA (100%/115% x TODA) The OEI is still required to meet 35' in 100% of the TODA following a failure 1 sec prior to V1. The dots are as follows...
....
If on 4 engines you don't get to 35' at the end of TODA, then it is purely chance that you have survived, as you did not have an engine failure at V1. Doesn't matter if you are Chuck Yeager or Wonder Woman, if you don't have the energy, you are compromised.
For a 4 engine aircraft, the AEO case is usually the limiting case that must be met, which is to attain 35' in 87% of the TODA (100%/115% x TODA) The OEI is still required to meet 35' in 100% of the TODA following a failure 1 sec prior to V1. The dots are as follows...
....
If on 4 engines you don't get to 35' at the end of TODA, then it is purely chance that you have survived, as you did not have an engine failure at V1. Doesn't matter if you are Chuck Yeager or Wonder Woman, if you don't have the energy, you are compromised.
