Use Of Reverse Thrust & Wet Runway

[Ops_Room_Junkie]

I wonder if anyone can help, specifically, with regards to the origins of a statement I have found in a company (not ours, duing audit) operations manual.

USE OF REVERSE THRUST
Note: Reverse thrust should be used as indicated in type specific
manuals.
It should be noted that safety levels are likely to be affected to an
unacceptable extent if reverse thrust is not selected when:
1. The runway is wet and the landing distance is less than 140% of
the landing distance required.

Now my company does not take credit for use of reverse thrust on dry/wet runways as per EU-ops and I cannot find any reference to the above in EU-Ops (JAR-Ops) or the aircraft manufacturers data. I 'think' the CAA used to allow credit for reverse thrust on dry/wet runways when certifying data, prior to EU/JAR-OPS but this is a very faint memory as I have not been around that long (honestly!).

Can anyone help?> I really hope that John Tull or Old Smokey might be woken up to have a pitch at this for me!

with thanks to all
ORJ

[de facto]

Ops -room,

I am very sure (not 100%) that this 140% is an internal SOP regulation and nothing else.

Under Ops1, Dispatch must make sure that the available DRY Runway Landing Distance(DRY at the scheduled ETA) is equal to or more than 1.67 x the QRH DRY ACTUAL Landing distance(NO REV,Auto speedbrakes,MAX MAN Braking).

Wet figures must be factored by an increased 15%.

Using full Reversers on wet runway is necessary for the reasons you may know as a pilot so I believe the company you are referring to, just wants to make sure than IN FLIGHT the flight crew calculates their landing distance (as required by EU ops) via the QRH as conditions may have changed from the time the aircraft was dispatched.(ie unscheduled rain).
(The QRH only factors 15 % for braking action GOOD(runway wet)).
The 1.67 isnt a regulation in flight anymore so the airline wants to make sure the the flight crew Landing distance Available is not 115% the landing distance Required but 140%...an extra margin as we aint all great super pilots.

Comparing your calculated and actual landing distance with specific a/b settings will not only improve your daily landing distance awareness,save unnecessary high or too low A/B settings and may also one day save your AA butt(:E) in case the runway is changed at the last moment.A quick check will allow you to accept or not the given landing runway.

Hope that helps

[Ops_Room_Junkie]

De Facto.

thanks very much for your reply. :ok:

Using full Reversers on wet runway is necessary for the reasons you may know as a pilot ....and that is the problem for me, I ain't a Pilot.
Trying to interpret regulations, performance is one thing - knowing what it's like to fly the damm things is another.
Not all performance people can fly and not all those that fly understand performance. I am lucky that I have some really good pilots who I can run things past and they in turn do the same with me. I have met some really superb peformance people who are pliots and have knowledge of some at the other end of the scale..

As a company we always use wet runway data for dispatch (the Captain can over-ride only if the weather reports show dry AND he needs the extra weight). In additon we also require crew to conduct another check post dispatch prior to arrival on actual WX reports).

Your reply was very much appreciated and helps me to build a better picture around this statement. Thanks again

[411A]

I 'think' the CAA used to allow credit for reverse thrust on dry/wet runways when certifying data, prior to EU/JAR-OPS but this is a very faint memory as I have not been around that long (honestly!).


The UKCAA most certainly did with one aircraft type, the Lockheed TriStar, as I have noticed it personally in one airline's ops manual.
In addition, it is my understanding that Boeing has approved, for USFAA registered B737-800 aircraft, a similar allowance.
Those that fly this latter type under FAA rules will undoubtedly have more information.

[RAT 5]

Slightly drifting off subject: aplogogies, but prompted by your statement about using 'wet' for takeoff as standard. In the 80's I used to work for an airline that followed your policy. However, I now work with one where we are supposed to calculate dry & wet, when dry, and use the more limiting. The reason being that wet, due to the lower screen height of 15', could give a higher MTOW than dry. I suspect that when dry most crews just go with that. Time is too tight to do double work. Thus I do not know when, or how often, wet would give a higher figure. I suspect it would only be so on long rwys where the lower screen height is useable. On short rwys I suspect the stop case will reduce the wet MTOW. Thus, it would seem, that to say wet MTOW will always be lower than dry and therefore give a buffer is not true.

[de facto]

You are very welcome :)

[de facto]

RAT,

He mentioned using WET figures for dispatch (Landing) not T/0.I guess their pilots may come to be restricted by their Landing weight for a given runway,so they use the actual dry landing distances ( reducing their company standard dispatch landing distance by 15% (they use wet as standard) so that for the same runway length they increase their company allowable performance landing weight(more fuel?pilots point of view?or pilots sense of business for the airline by carrying more load?).

Also I doubt pilots would use wet speeds as standard for obviously dangerous perf problems after a GO decision:E

411A,

EASA countries do not include reverse credit on DRY runways for Take off (only WET) on the 737 as it was done for its certification by boeing (under FAA rule) and no reverse credit for DISPATCH landing distances on dry or wet.
In flight QRH landing distance do credit for reverse use depending on A/B setting and runway friction.
I dont see any reason why the FAA would do otherwise.

[decurion]

Have a look in the following report: http://www.nlr-atsi.nl/eCache/ATS/14/919.pdf , section 5.2.3.

Note that thrust reverses are most effective on slippery runways. On dry runways tire braking can add a lot more to the total deceleration than reversers (there are some good articles on this by Boeing).

[safetypee]

ORJ, as above from decurion, reverse is very effective on wet / slippery runways (N.B. ‘slippery’ is a Boeing term which includes wet / very wet).
See ALAR Briefing Notes in English | Flight Safety Foundation (http://flightsafety.org/current-safety-initiatives/approach-and-landing-accident-reduction-alar/alar-briefing-notes-english) , chapts 8.4 & 8.5, where diagrams show the components of braking.

Although reverse is not included in EASA dry / wet landing performance, incident statistics suggest that many pilots rely on reverse to rescue unforeseen / poorly judged situations, thus its use is recommended by internal SOP.
Note that when using EASA contaminated landing performance, reverse thrust may be assumed, if so then it must be used. The performance data should be annotated as such and details provided of limiting circumstances and/or assumptions (CS AMC 25.1591). EASA - Certification specifications (http://easa.europa.eu/agency-measures/certification-specifications.php)

The reference to 140% is unusual. Either the operator follows FAA type rules with airborne assessments calculated as suggested in posts above, or if an EASA operation, a particular interpretation of EU-OPS 1.400 is used. I.e. a requirement for safe approach and landing – if a 1.92 factor is required for dispatch how is 1.4 factor in the air, justified as being ‘safe’?