Braking action

[inner]

Hi

Got a small question. If you find in the metar 'braking action good', is this derived from pilot reports or just by friction measurement?

Dont find the answer.

[safewing]

inner

A common gotcha is the fact that braking actions usually come from a snowtam decode which is part of the notam system.

Although a braking action may be appended onto a METAR the time of the report will be found in the NOTAMs and will most likely not be the time of the METAR issued.

The reference to good in the braking will relate to the time it was issued in the notam. If it is actively precipitating the chances are the braking action has deteriorated.

It is possible to see a braking action that was reported 10-12 hours earlier still valid because it hasnt been updated.

[Airmanson]

I believe it's from braking coefficient measured by special airport vechiles.

[A Squared]

In the US, braking action classified as good, fair, poor, etc is always from a pilot report. The type aircraft aircraft should be included with that. Ant braking action that is from a measuring device will be reported as the measured values. I've never seen either reported in a METAR, though.

[Fokker-Jock]

I've never seen a "Braking action report" in a metar.
Motne reports are however quite common at the end of a metar, but I guess that's not what you are talking about ?
Snowtam is part of the notam.
I'm more used to braking action reports in an ATIS.

[9.G]

The friction coefficient report is a standard item in EE at the end of the ATIS and runway condition at the end of metar. Snotam is useless for the real time evaluation of the runway condition before commencing the approach. As for PIREPS, well very subjective and hardly reliable. :ok:

[inner]

Fokkerjock, you are right. The words itself you dont find in the metar. But i was more referring to the numbers associated with and especially how they get these numbers. The reason is also, if i for example you see the number 95 (braking action good), how to interpret these numbers.

[safewing]

A braking action on an Atis can relate to a runway surface condition as well as the environmental situation .

So if the Tarmac or concrete surface has deteriorated below a nominal value of friction, airports are obliged to report a braking action even in the height of summer.

Braking action values are based on the equipment used at the airport. Outside of Canada which use CRFI nationwide the value will vary based on whether it is skiddometer Saab mu meter or whatever device is used.

The last 2 digits of a MOTNE can either be a friction value or can be a braking action.

I'll correct myself and say that the MOTNE is independent of the Notam system, apologies for the confusion. But the premise that a MOTNE may not update with the METAR time is correct, or alternatively it can mean that there is no significant change to the report

[safetypee]

ICAO Annex 3 (Met) provides guidance on the format for METAR (Appx 3). A METAR may provide runway state under supplementary information. This is reported as either friction coefficient or braking action, expressed as nn or //.
The numerical format appears to be as used in a SNOWTAM – ICAO Annex 15 (AIS), where runway friction is reported in either a two digit or single digit format (measured/calculated vs estimated friction; Good - Poor, 5 - 1). The decode for this is in Appx 2, or ICAO Annex 14 (Aero) Vol 1, att A, para 6.

Thus it is possible for METAR “braking action” - estimated friction (single digit), to originate from a PIREP, but as noted in reports below, ICAO does not define braking action or its origin, which adds to any subjective inaccuracy of a PIREP.
A two digit report would indicate measured friction, but this also is subject to many inaccuracies.

The ICAO Cir 329 ‘Runway Surface Condition Assessment, Measurement and Reporting’ (www.iata.org/iata/RERR-toolkit/assets/Content/Contributing%20Reports/ICAO_Circular_on_Rwy_Surface_Condition_Assessment_Measuremen t_and_Reporting.pdf) provides the most recent guidance, which aims to improve understanding of surface friction characteristics and their contribution to landing safety. Recommendations as to measurement and reporting will be considered by ICAO.

In particular, note the significant misgivings about operational friction measurement which more often does not relate to ‘braking action’.

In parallel with the ICAO work, the FAA Aviation Rulemaking Committee (ARC) working on Takeoff and Landing Performance Assessment (TALPA) has made several recommendations (www.skybrary.aero/bookshelf/books/1508.pdf).
Note the move away from subjective assessment of braking action (PIREPS) and cautions about friction measurements.

Re the minimum friction standard for a wet runway (i.e. runway maintenance; surface deterioration - #8)
The recommendation is to reducing the effective braking action for a wet runway from “good” to “medium” when the runway is designated as “slippery when wet.”

[JulieAndrews]

I understand FAA-world is ahead of EASA-land in this respect?
Can anyone here update what the latest is with EASA's initiatives to use connected aircraft braking sensors reporting directly into AIS?

[Skornogr4phy]

We have those connected sensors fitted in our fleet, but I have never seen them produce a report. The anti skid has to engage before a braking action can be reported, and even on wet runways we are unlikely get that to happen. In the winter in some northern countries we probably get a report from it, but for the airports we fly into (usually large city airports) they are very good at runway clearance.