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No REV on wet RWY: RLD

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No REV on wet RWY: RLD

Old 2nd Jan 2022, 01:34
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Only half a speed-brake
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No REV on wet RWY: RLD

FCOM: Dispatch on wet Runway

Landing performance is calculated without the benefit of thrust reversers, as per regulation. RLD(wet) = RLD(dry)*1.15

Different from what I remembered, or is the grey matter damaged? No access to G2G for today, irrespective of the publishing date.

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Old 2nd Jan 2022, 16:30
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FD,
As I recall (EASA land) reverse is not considered at destination in dispatch calculations. However, … wait for it … operational requirements may change due to the application of ‘TALPA’ performance as required by Certification Specification CS-25 Amendment 27 (change info, retrospective application, at page 14 onwards -(https://www.easa.europa.eu/downloads/134260/en).

This suggests that dispatch to a contaminated runway can use reverse where approved by new calculations for contaminated surfaces. Additionally to a wet runway classified as ‘Slippery Wet’ (code 3) n.b. previously / same as Slippery When Wet as in NOTAMs. Note potential confusion with with Boeing / FAA terminology involving slippery runways.
FAA position uncertain; new ‘TALPA’ contaminated performance data should be applied ( as 25.1592/92 ), but a get out of … via AC 25-32
Landing Performance Data for Time-of-Arrival Landing Performance Assessments (para 11) https://www.faa.gov/documentLibrary/...r/AC_25-32.pdf


EASA briefing (at time of arrival):-
https://www.easa.europa.eu/downloads/125411/en

Other relatively new references:-
ICAO Circular 355 Assessment, Measurement and Reporting of Runway Surface Conditions
pilot relevant info throughout the document
https://www.icao.int/WACAF/Documents...55_cons_en.pdf

ICAO Doc 10064 - Aeroplane Performance Manual ( Feb 2020 ?)
again, pilot relevance throughout
https://www.sapoe.org/wp-content/upl...rce.pdf#page60
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Old 3rd Jan 2022, 01:34
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Many thanks, this will keep me amused for days.

Think you nailed it in the first sentence, possibly I got it mixed up with TKOF.
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Old 3rd Jan 2022, 08:54
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Ewww those are long and tangled docouments. I suspect I too will be busy for some time. A first read gives a new value (new to me at least) for hydroplaning speed on p22 of the CS25 amendment as far as wheel/ground friction is concerned. "For the purposes of estimating the effect of aquaplaning on contaminant drag, the aquaplaning speed, VP, is given by - 𝑉𝑃 = 9√𝑃 where VP is the ground speed in knots and P is the tyre pressure in lb/in2 . To estimate the effect of aquaplaning on wheel-to-ground friction, the aquaplaning speed (VP) that is provided above should be factored by a coefficient of 0.85." I also notice that Appendix 5 of the ICAO doc (page 55) assumes a 1.67/60% factor on dry runways for turboprops.
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Old 3rd Jan 2022, 10:59
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swh

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Originally Posted by FlightDetent View Post
FCOM: Dispatch on wet Runway

Landing performance is calculated without the benefit of thrust reversers, as per regulation. RLD(wet) = RLD(dry)*1.15

Different from what I remembered, or is the grey matter damaged? No access to G2G for today, irrespective of the publishing date.
This is correct for dispatch landing performance, in flight performance differs. In flysmart it is the dispatch and inflight on the top left in the landing performance application.

A REV inop MEL has no impact on dispatch landing performance, where inflight it does. You can try this with in flysmart.
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Old 3rd Jan 2022, 19:28
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Its more that airbus didnt explain well in the FCOM the definitions between dispatch and inflight calculations. Those are notes from an old slide that I cant find.

RLD = 1.667xALD
ALD= 4,5 sec flare, assumes Vls at 50ft, no REV for dry or wet, MAX manual braking, Vapp at touch, Vls if athr off.
LD (in flight)= 7 sec flare, 96% Vapp at touch, credits as selected in flysmart
FLD (Factored LD)= LDx1.15

With inflight failures we go to the last 2. Without, we go to the dispatch.

What drove me crazy for long time was the takeoff performance in wet. Its calculated with 2 reversers in wet. Do a takeoff run in flysmart with runway limited numbers and zero margin. Lose an engine and your reverse is inop now. Well, you are out of the runway. (Play with reverse inop MEL item for the same takeoff)
Yes, I know, the 2 seconds at V1 speed but, that drove my OCD for long time! V1 is the speed where if you lose an engine you would have taken the desicion to stop within the remaining runway! LOL
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Old 4th Jan 2022, 02:12
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Thank you for the input, Lantrin.

In return for your trouble:
The V1 stop case of course accounts for REV (credited on wet) to full stop - on the remaining engine(s) only.

The difference you see with 1x REV inop results from the limiting case when the opposite engine fails. ASD then has 0 REV.

I assume, please check by running the numbers for NO REV.


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Old 4th Jan 2022, 10:37
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Hi flightdetent. Thanks for your reply and sorry to bomb your thread.

I have checked that many times and I checked again to be sure and it’s crazy. When you calculate ASD with wet it’s 2 reversers credit. If you use MEL one reverse inop, you get 1 reverse credit only.

The paradox is that, with that MEL now you are not allowed to takeoff. Where in dry there is no issue as no reverse was calculated. So, what happens when you lose an engine in wet, and abort? Go for fishing I guess.

Check my uploads below for A321 in LFLL intersection takeoff A4 on 17R, wet

I don’t know if you have access in flysmart,
you can see the credit on the “REV FOR COMPUTATION” box.

First picture, no MEL, TOW limit 80.7 “All reversers operative”

Second picture, 1 REV inop, TOW limit 79.5 “One reverser inoperative”

Third picture, 2 REV inop, TOW limit 78.7 “All reversers inoperative”






So there are 3 different setups here.


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Old 4th Jan 2022, 11:57
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Only half a speed-brake
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Please worry not, you have concluded my question already. The floor is open...
Moreover, learning about things we did not know is the most exciting part.

For your case, however, I'm outwitted.

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