Originally Posted by
iceman50
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.
Ice;
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.