Winter operations - the ATC perspective

[LYKA]

Hi all,

Can I ask if there is a set of limitations [snow depth] that are applied before the runways in the UK are closed? With the possiblilty of bad weather this week it would be interesting to know that runways will be closed with xxx mm of wet snow etc. I do apprieciate that the braking action measurements become unreliable in wet snow but at what satage will the BAA say to you guy's enough. It would be sad indeed to end up in the same situation as a couple of years back with airport after airport closing its runways as we were on our diversion to it!

[Jerricho]

Winter operations you say................bah ;)

[TheOddOne]

I do apprieciate that the braking action measurements become unreliable in wet snow but at what satage will the BAA say to you guy's enough.

It's a difficult question to answer simply so it's well put.

Firstly, though, we have no manner or means at present to measure braking action. All we can measure is surface friction. The two are often confused but are different animals. There may well be some sort of rough correlation between the retardation of brake application and the friction of the surface; much work is being done at the moment to establish what this might be, but it ain't done yet.

I guess the point at which I will decide when to declare the runway closed for contaminant removal will in part depend upon when pilots refuse to continue using it and what the forecast is. We had a light shower of snow the other day which produced a covering on the runway which made it look white but it was very thin (<1mm) and no-one reported a loss of braking action. As both the air & ground temp were >+4C it melted very quickly and I decided to take no action. However, another scenario might be that the forecast is for the snow to continue, in which case I might decide to close early and start sweeping to prevent a build-up that will be more difficult to remove later.

We have a system at LGW where GAL, ATC the major airlines and the Handling Agents all get together to co-ordinate timings of this operation and what the order of flight will be when we re-open.

An alternative to sweeping, where falls are expected to be relatively light, is to apply ant-icing fluid instead of sweeping. This takes a closure of 12 mins to apply fluid that will melt falling snow up to 10mm down to a temp of -5C. The holdover of this fluid is quite good provided it doesn't get washed away by rain before the snow starts (which is quite common in SE England). The fluid itself may reduce surface friction slightly but not below that experienced with a wet runway so we normally declare 'wet, wet, wet' after treatment.

As I expect you all know by now, we're not allowed to publish friction readings during adverse weather, so forget that 'icy' table. Our policy now is to keep working on the runway once it's closed until we get back to black and it's in the 'wet, wet, wet' band.

Cheers,
TheOddOne

[LYKA]

Thanks very much oddone.

If I may 'dive in' a little further. Our definition of a wet runway is less then 3mm of water or equivalent on the runway. Is that what you guy's work to? If so could we resonably expect to land on a runway with say 2mm of wet snow after it has been swept etc?

[TheOddOne]

LYKA,

Our aim is to restore the runway surface to black. We would continue sweeping and treating with de-icing fluid until at least 75% of the surface is black. In practice, we would try to ensure that all of the surface either side of the centreline is clean, with any contaminant consigned to the outermost edges.

Cheers,
TheOddOne

[southern duel]

Thanks

Odd One

saved me writing all that !!!!!!

your colleague from LHR !!!

Mind you we have 2 runways which helps !!!

:ok:

[Evil J]

And ofcourse non-BAA airports don't get any snow!!!

[TheOddOne]

Evil J,

Of course not, all that white stuff is a pigment of your imagination (sorry, been a long day on a mgmt training course, I'll get me coat...)

Cheers,
TOO

ps Bst rgds to all who are out tonight either pushing it about or trying to melt it with Clearway. Ahhhh for the days of Urea and Konsin!

[peatair]

I don't remember there being any actual figures for snow depth etc. set out at which an airfield must be closed. In the U.K. it is the Airport Management - not ATC - who have responsibility for making this decision. It can be a very difficult decision.

The airport personnel have to inform ATC of the "runway state" and ATC are responsible for passing this information to pilots. As always, the final decision as to whether to operate rests with the pilot in command.