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When is the best time to run runway friction tests?

And what is the optimum temperature to run them?

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    $\begingroup$ "optimal" w.r.t. which parameters/constraints? $\endgroup$
    – Federico
    Oct 6 '20 at 13:46
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The friction will change over time due to temperature and moisture and other factors.

So, the best time to measure is shortly before a plane is about to land. In order to allow planning of alternatives, allow a longer time.

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I found a couple of FAA sources on this, I don't know if other countries have similar guidance or not. The FAA information covers two reasons to measure runway friction: for maintenance, and for operations in winter (ice etc.).

For maintenance, the information is in AC 150/5320-12C - Measurement, Construction, and Maintenance of Skid Resistant Airport Pavement Surfaces. The PDFs seem to be corrupt for me (missing and blank pages), but the draft version looks better. It recommends basing inspections on the minimum number of turbojet aircraft landings per runway end each day; see table 3-1 on page 8. The frequency ranges from a minimum of once per year for less than 15 landings up to once per week for more than 210 landings.

Because that's a draft and the published version doesn't work correctly for me it's possible that the published values are different.

For winter operations, the guidance is in AC 150/5200-30D - Airport Field Condition Assessments and Winter Operations Safety. There's no strictly defined frequency that I could see although it does mention four situations in which the airport should do a friction survey (section 5-2-1):

  • There's a specific amount of ice or snow on the runway, and the operator "believes the information will be helpful"
  • The runway centerline is contaminated for a distance of more than 500ft
  • "Following all snow clearing, anti-icing, deicing, or sanding operations"
  • Immediately after any incident or accident on the runway

Both ACs have a lot more information in them.

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