Jwscud, a minor but perhaps important point is that a primary aim of TALPA is to replace measured friction as a means of reporting because it is unreliable. Thus your point might be to degrade the ‘declared braking action’ by 1 for sand, not the measured value, because they might not be the same.
However, where the braking action is based on the type and depth of contaminant as in TALPA, sand is not considered except as noted: “While applying sand or liquid anti ice to a surface may improve its friction capability, no credit is taken until pilot braking action reports improve or the contaminant type changes (e.g., ice to water).” This is interesting because ‘pilot braking action reports’ in TALPA, presumably PIREPS, should not be used to upgrade the braking action, only downgrade them.
From the FAA briefing on TALPA trials (33rd Annual Airport Conference), “Pilot reports are divided fairly equally in their opinions of sanding/treating the runway improves or doesn’t make a significant difference in the braking action that they experience for the contaminant conditions reported”.
Thus via TAPLA, sand may not/does not change the braking action, but as yet there is no means of assessing the braking action of a sanded runway except by using mu meters which can be unreliable.
Yet again the regulators place the responsibility for safety on the operator, but without advice to help them.
ICAO Circular 329 considers sand thus:- “… the effect of non-melting ice conditions can vary considerably depending on the smoothness of the surface, whether it has been treated with sand or melting agents etc.”
Elsewhere it discusses sand as a contaminant (presumably on a hard surface) which degrades the braking action.
FAA AC 150/5200-30C discusses the use of sand but offers little operational advice: “… sands do not perform the same. In general, the greater the quantity of sand applied, the greater the increase in traction. Fine sands show superior performance on warmer ice (>20° F (-7° C)), while coarser sands show superior performance on colder ice (<15° F (-9° C))".
Thus downgrading the braking action by 1 seems a good policy, but if the downgrade gives ‘poor to nil’, should you operate.
Also, what is the basis of the reported braking action; is this before/after sanding, and by what means was it obtained.
Other references to sanding appear to be from local authorities (Sweeden); what is the view of the certificating (AOC) national authority (UK)?