Takeoff Distance
Author Topic:   Take Off Distance
Magic Blue
PPRuNe Line Training

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Registered: Jan 2001

posted 16 February 2001 18:23     Click Here to See the Profile for Magic Blue   Click Here to Email Magic Blue     Edit/Delete Message

Can any of you pro's help me here.If your aircraft is at the max take off weight for the conditions,runway length etc.How much runway length should be left after VR.

Do pilots know the exact distance that they will use on a take off run and not just the t/o speeds etc.

Finally,if you do know the distance,how can you work it out.

Appreciate any information

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411A
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posted 16 February 2001 19:30     Click Here to See the Profile for 411A   Click Here to Email 411A     Edit/Delete Message

Very litte runway is remaining if the takoff weight is runway length limited. Can recall, for example, departing from Rny 27 in Fukuoka Japan at 504,000 pounds (runway limit for the conditions) in a L1011-500 and noting that Vr was within 500 feet of runway end. Also recall the F/O had mentioned that if we tried to stop at V1, we would have ended up in the bay, and he was absolutely right!

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Zeke
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posted 16 February 2001 19:43     Click Here to See the Profile for Zeke     Edit/Delete Message

Normally airliners have a book that is specific to the airline and the aircraft type called a "runways analysis manual".

You just look up the correct runway and the correct airport, and enter the chart with aircraft weight and wind component. Some operators do not use the advantage of a headwind, but deduct the disadvantage of a tailwind.

It is rare to use full takeoff power, normally we tell the engine its actually hotter outside than it actually is so it give a "reduced thrust takeoff".

Another technique used on long runways in areas where you have steep after takeoff climb gradients is to increase the speed the aircraft while the aircraft is on the runway so we have more energy than absolutly necessary to get airborne to we can get better performance in the event of engine failure.

You may be interested in reading a report issued by the flight safety foundation which takes about takeoff performance.

"Recent revisions of the U.S. Federal Aviation Regulations and the European Joint Aviation Requirements redefine V1 as the maximum airspeed at which a flight crew must take the first action to safely reject a takeoff. Other revisions change the method of compensating for the time required by pilots to take action to reject a takeoff; require accelerate-stop data based on airplanes with fully worn brakes; and require wet-runway takeoff-performance data in airplane flight manuals"


report : http://www.flightsafety.org/fsd/fsd_oct98.pdf

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Lucky Angel
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posted 18 February 2001 09:32     Click Here to See the Profile for Lucky Angel   Click Here to Email Lucky Angel     Edit/Delete Message

The answer is that you have to be at 50ft in the air by the end of the rwy.

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Fly high be safe !!

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mustafagander
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posted 19 February 2001 00:30     Click Here to See the Profile for mustafagander   Click Here to Email mustafagander     Edit/Delete Message

Lucky Angel,
I think you'll find that the screen height at the end of the TODA is 35ft.

Just to clarify, the distances for the same take off are TODA-Take Off Dist Avbl, used in the all eng/1 eng inop go case, TORA-Take Off Run Avbl, used in the all eng/1 eng inop go case and ASDA-Accel Stop Dist Avbl, used in the RTO case.

TORA is the physical length of the runway avbl.

TODA can include clearway up to a defined length.

ASDA can include any stopway avbl.

Clearway is an obstruction-free area over which you can fly to achieve screen height, e.g. water.

Stopway is a surface on which you can finish stopping in the event of RTO. You may damage the surface and/or be unable to taxi off stopway e.g. grass overrun areas.

Obviously you must be airbourne by the start of clearway or stopway.

Magic Blue,
At Vr there may not be much runway left at all.

Unlike 411A, I am a "believer" in the performance calculations. Given that the actual conditions match those for which the calculations are derived, you WILL stop at V1. Remember, almost none of us has ever done a max energy stop in the a/c. When I was a performance engineer in a previous incarnation Boeing convinced me. Then I saw a pal do a full-on RTO from V1 and it worked well. The runway was field length limited for the weight, but they stopped about 250ft prior the end - about the margin reverse gives. The brakes (on a B747 classic) were welded in about 5 minutes, but they stopped.

[This message has been edited by mustafagander (edited 19 February 2001).]

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Dave Incognito
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posted 19 February 2001 06:58     Click Here to See the Profile for Dave Incognito   Click Here to Email Dave Incognito     Edit/Delete Message

A little more than this perhaps?

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Flying is easy - just throw yourself at the ground and miss.

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4dogs
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posted 19 February 2001 14:50     Click Here to See the Profile for 4dogs     Edit/Delete Message

Mustafa,

The reference to screen height is potentially misleading - it only applies to OEI takeoff and only when TODA limited. The AEO case should be higher, typically 125-150 ft I seem to remember (depending on the number of engines actually running!!).

I have it on good authority that the CX photo is not uncommon TORA height and that having wheels still on the ground at the 450m to go markings is also not uncommon. Mind you, I am not sure that the latter example matches the OEI ground roll requirements.

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quid
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posted 20 February 2001 21:02     Click Here to See the Profile for quid   Click Here to Email quid     Edit/Delete Message

MB
If all engines are operating (which thankfully is usually the case), there must be 15% additional runway remaining at liftoff.

If an engine failed at V1, and you crossed the end of a 10,000 runway at 35', then in the case of AEO, you would liftoff approx. 1300 feet sooner.

Sometimes it "seems" like we're using every foot of it, though. A slow rotation rate makes it look worse than it is.

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Elevation
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posted 21 February 2001 11:20     Click Here to See the Profile for Elevation   Click Here to Email Elevation     Edit/Delete Message

Don't recall Fukuoka, Japan having a Rwy 27.
It is 34/16, and yes, it is SHORT.
I do recall the figure of 35' at the end of the rw with all engines operating. 15' in case of an engine failure.

The usual practice for a wet runway V1 is to take 10kts off the dry runway V1. This works well if the rw is clean and has a lot of grip, if on a wet rw with plenty of rubber deposits, the RTO may very well be tricky to say the least.

Cheers.

[This message has been edited by Elevation (edited 21 February 2001).]

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HighSpeed
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posted 21 February 2001 16:19     Click Here to See the Profile for HighSpeed   Click Here to Email HighSpeed     Edit/Delete Message

gents,

quote:



the FAR takeoff field length is the LONGEST of the following:

1. the distance required to accelerate with all engines, experience an engine failure, continue the takeoff and reach a point 35' above the runway at V2 speed (accel-go)

2. the distance required to accelerate with all engines, experience an engine failure, recognize the failure, initiate the stopping maneuver and stop within the confines of the runway (accel-stop)

3. 1.15 times the all engine takeoff distance required to reach 35' above the runway


interestingly, most of the discussions here centered on 4-eng acft. on 4-eng acft, it is most likely runway limited because you only lose 25% thrust unlike a 2-eng acft which will be climb limited cos you lose 50% of thrust. i recall clearly when i was on the 747, on a field length limited takeoff, Vr is about 2000' (runway edge - amber) from the end whereas now, i'm on the b777, on a field length limited takeoff, there's probably about 4000' left.

HS

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m&v
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posted 21 February 2001 16:53     Click Here to See the Profile for m&v     Edit/Delete Message

The 'regulations'stipulate that aprox'(57%)distance from VR to screen height must be over Runway.This is where'clearway'comes into play.This is the third distance required after Accl/stp..Accl/go..All engines Distance +15%
It becomes a concern when JAA allow you to use'clearway'(500/1000')to get to your'wet'15'screen-one crosses the end at about 10'......thoughtful eh

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quid
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posted 21 February 2001 18:50     Click Here to See the Profile for quid   Click Here to Email quid     Edit/Delete Message

The "climb" limit has nothing to do with the length of the runway. It is simply a gradient attainable at a certain density altitude. (Further, it has nothing to do with any specific airport.)

Obstacles, on the other hand, ARE runway specific, and have to be factored in the max TOW for "that" runway.

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HighSpeed
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posted 22 February 2001 01:09     Click Here to See the Profile for HighSpeed   Click Here to Email HighSpeed     Edit/Delete Message

agreed that climb limit is not runway specific but the point i'm trying to put across is the difference in runway remaining at VR for 4-eng and 2-eng acft.

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