WET runway data
 

I have some data on landing performance (e.g. peak N1 during Thrust reversers usage). I would like to know if the runway was wet at the time of measurement. We want to sort landings into wet & dry to see the difference in TR usage. We have assumed SOPs require TRs to be deployed for all landings (but the supposition is that TRs are used more when wet).

Unfortunately this fact (WET/DRY) wasn't recorded in my data but can I make any assumptions from relative humity values.

From another post ... "A runway is considered 'wet' when the runway surface is covered with water or equivalent, less than 3mm or when there is sufficient moisture on the runway surface to cause it to appear reflective, but without significant areas of standing water."

100% RH means it might rain but has it actually rained?

What should I look for? Is RH recorded on the aircraft somewhere? Alternatively is it a purely ground-based (MET-office) recording?

Relative Humidity is a purely ground-based (MET-office) recording, and not recorded on the aircraft.

Even if your research turns up that the RH was 100%, that doesn't imply a wet runway, simply that it is about to, or is raining.

If you can establish that it was raining from RH, it may be only a light "sprinkle", leading to, at the most, a slightly damp (non-wet) runway. Of course the opposite extreme of a well flooded runway also applies.

Regrettably, I believe that chasing RH records will not lead you to the results that you seek, sorry to rain on your parade :)

Regards,

Old Smokey

Or put another way, if you're prepared to wear your best pants and sit down on the runway - it's dry. If not - it's wet:ok:

Sir George Cayley

To determine the wet or dry nature of the runway might be possible based on looking at aircraft stopping performance. Depending on how good your data is, of course, and depending on type - an autobrake type that targets decel rate wont tell you as much as an older type without autobrake I suspect.

If you have good data for the braking system you could perhaps look at a/skid behaviour.

I suspect you only have QAR/FDR type data, though, and it would be very difficult to use that for these purposes as the frequency is probably too low.

Why not do things the other way around - instead of trying to establish wet/dry for all data points, only use data points where you can be confident (to an acceptable level) of the runway conditions.

Check the weather reports for an airport where you have lots of data (one of the hubs, perhaps). Find a day where it didn't rain at all - dry for sure. Use all data that day as "dry". Find another day where it rained for a long time. Use data from that time period as wet. Bin the rest of the data.

If you see no strong difference in TR usage between the "known dry" and "likely wet" data that'll tell you what you want to know I think?

Indeed you could even compare the "known dry" data to all data - if the usage pattern differs between the dry subset and the rest, that implies the usage is different on non-dry days.