Contaminated RWY

[JRC0001]

Hi folks,

Anybody could be so kind to help me with a small doubt regarding Contamination Depths and correct calcolation ?

We all use standing water equivalent table when we are calculating our performance, my question is quite simple and is: what kind of performance you use if the contaminant (standing water, slush or snow) is reported but below the limit to be consider contaminated.

Example:

ATIS REPORT : 5mm of loose wet snow
AFM report that the rwy is consider contaminated of loose wet snow with 7mm and is providing calculation for 7mm and 15mm

Do you use: Loose wet snow 7mm, Slush, wet, or dry performance? and why?

Do you have any reference of EASA/FAA regolation that is answaring at my question?

Thanks for the help

[PEI_3721]

There may not be an consistent answer - now; depending on the regulator for rules and guidance, and aircraft manufacturer for performance data.
Many aspects are changing or are planned to change this year.
Reporting of runway condition will be based on a new / revised matrix. RCAM
Aircraft performance should reflect revised data more representative of actual operations and runway conditions. Airbus aircraft already have this data - OLD / FOLD.

Background:- https://www.icao.int/EURNAT/Other%20Meetings%20Seminars%20and%20Workshops/GRF%20Workshop%20(Frankfurt)/GRF%20Wkshp%20FR%20PPT01.pdf
See slide 28, the runway condition description (contaminant / depth) will relate to a condition code, then aircraft performance can be determined from manufacturers data.
Which aircraft manufacturer ?

Tech Ops Performance:- https://www.icao.int/EURNAT/Other%20Meetings%20Seminars%20and%20Workshops/GRF%20Workshop%20(Paris)/GRF%20Wkshp%20PPT06.pdf

Airbus view: - https://www.icao.int/Meetings/grf2019/Documents/Presentations/GRF2019%20S2%20Lars%20Kornstaedt%20-%20Airbus.pdf
See slides 10 - 11, reported contaminants and depth.

EASA:- https://www.icao.int/EURNAT/Other%20Meetings%20Seminars%20and%20Workshops/GRF%20Workshop%20(Paris)/GRF%20Wkshp%20PPT03.pdf

[error_401]

In some instances the operator has to define what to use.

In my outfit we use "wet" for all runways where some form of contaminant is present but below the limits of being considered contaminated.

Your special case mandates a "contaminated" calculation as I have to assume your "5mm of loose wet snow" is present on more than 25% of the surface.

"Loose" is not a qualifyer used in RCAM or any reporting. Which put's you into the table for 5mm wet snow.
For performance calculations you have to use the RCAM table from the AFM or operators, similar to this one (FAA - but it's pretty much the same for EASA)
https://www.faa.gov/about/initiatives/talpa/media/TALPA-Pilot-RCAM.pdf

It puts you into RCAM 3/3/3 which is at least "wet" or "contaminated". Usually performance tools are able to calculate with wet snow over 3 mm depth because it is considered a contaminant. Depending on the tool i will tell you a water equivalent or simply do a calculation based on actual TOM or LDM and the result is either green or red. (go or no-go)

As for a basic approach to contaminants: Anything which sticks to the surface of a runway is a contaminant, regardless of what it is. Therefore "dry performance" is already out the window. Would you be comfortable driving your car down a slope with 5 mm of wet snow and you assume "only" a wet road? Do you think you need more braking distance, or less than on a wet road? If all your tables don't tell you exactly what that contaminant is you have already pointed out that you may use 7mm wet snow from the AFM as you have a table.

When the RCAM first came up I found myself in a situation where snow over sanded ice was reported with braking action "MEDIUM" but at that time I had no legal table to do a calculation based on braking action. Therefore we calculated it with "wet-ice" which is braking action NIL and the calculation came out green with 80 m remaining runway. Legally good to go we landed and left the runway at the usual taxiway about half way down. 1'400 m autobrake MAX, full reverse for the first 10 seconds, then all off as we would have stopped well short of any useful exit. The point is - good airmenship.

Hope this helps answering your question.

[Kirks gusset]

From our OMA:"Contaminated runway" means a runway of which more than 25% of the runway surface area within the required length and width being used is covered by the following:

surface water more than 3 mm (0.125 in) deep, or by slush, or loose snow, equivalent to more than 3 mm (0.125 in) of water;

snow which has been compressed into a solid mass which resists further compression and will hold together or break into lumps if picked up (compacted snow); or

ice, including wet ice.

As a general rule it's safer to use the most limiting conditions as ATIS reports are not always accurate in terms of time, consider the braking actions as a barometer and pilot reports from similar aircraft types.
Worth mentioning that landing performance and take off performance may be different for the same runway and our old ops manual stated with braking action less than "medium" it was a divert/hold etc.

[Check Airman]

FAA AC 25-31

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_25-31.pdf

A runway is wet when it is neither dry, nor contaminated. For purposes of condition reporting and airplane performance, a runway can be considered wet when more than 25 percent of the runway surface area (within the reported length and the width being used) is covered by any visible dampness or water that is ⅛ inch (3 mm) or less in depth.

Note: A damp runway that meets this definition is considered wet, regardless of whether or not the surface appears reflective.

[PEI_3721]

error 401, thanks for some useful observations.
However, beware a hazard in the last situation; braking feels sufficient with reverse, but when cancelled the brakes haven't been contributing very much on a slippery runway due antiskid / autobrake selection.

See the Boeing briefing on slippery runways - http://www.vipa.asn.au/sites/default/files/webform/ddr/130923%20wet%20runways.pdf
Slides 14-17 graphically illustrate the hazard with autobrake and reverse on low friction runways.
Pilots may 'think' - seat of the pants sensation - that deceleration is satisfactory, but in reality as the effect of reverse decreases with speed reduction, and particularly if reverse is cancelled, the brake contribution is low to nil; pilots suddenly sense that the aircraft 'accelerates'.

Also, and as in more recent posts, the braking performance achieved depends on both accurate reporting and matched performance data.

Airbus has provided new OLD/FOLD data, but Boeing is unknown. Thus if the Boeing 'slippery' category has not been matched to the new runway condition reports then the performance expect may not be achieved. (No slippery category in RCAM). What is Boeing definition of slippery ?
e.g. in the Airbus presentation https://www.icao.int/Meetings/grf2019/Documents/Presentations/GRF2019%20S2%20Lars%20Kornstaedt%20-%20Airbus.pdf from slide 16. If Boeing slippery is somewhere within 'wet', (like RCAM 6 changing to 5) then then the additional safety margin needs to be 20 - 40%, much higher that the minimum 15%.

[error_401]

PEI_3721,

good point. That's the reason why I stressed autobrake to MAX and not to an intermediate setting. Simply because in a crosswind landing on contaminated runways I'm not good enough to perform 4 actions at the same time (touchdown elevator, rudder, aileron, thrust levers). The most important being to keep the rudder input, even increase it with deceleration together with the ailerons. Unfortunately we have less and less opportunities to actually land on contaminated runways.

A word of caution: Make sure your aircraft does a maximum braking with autobrake MAX and not a deceleration rate, in which case I agree with you that efficiency of wheel brakes may be covered by reversers. Now I'm not going to wait with reverser deployment longer than needed after main gear touchdown when landing in Tromsoe or such places at maximum crosswind for the contamination.

Couple years ago on the E190 when flying to the nordic countries quite a bit I have studied several runway overruns and found a major contributor in wrong rudder application. Interesting in this instance is that in many cases rudder went to neutral/center position with brake application and the crosswind upset the whole braking. This is the reason why I select autobrake to MAX and have all the time and concentration left to keep the aircraft straight with rudder and ailerons and apply reversers accordingly.