Performance on a damp runway vs wet/dry

[Sir George Cayley]

CALL 100 is on the right track, but to amplify remember the dynamics of the surface.

A runway state is always changing, especially in the UK's predominentaly Maritime airflow. A Wet runway is always shedding water. A Damp runway just means the drying process is nearly complete. In the UK, Damp is defined as visible staining of the surface by moisture.

The requirement to inspect and report the condition of the RWY is contained in CAP168 and for anything other than Sleepy Hollow Int'l is barely enough.

Ops Officers worth their salt have a weather eye and keep the ATIS informed as significant events, that may affect a/c performance, are observed. And, if ATC from their lofty tower want another gander, then off he goes. (Never mind it's the first meal break in 6 hours)

And how many of us have trundled to the hold on a luurvely summers day only to watch a midday shower drench the active just as your slot arrives
You screw up the calcs, tell Tower to wait one and crunch new numbers. You do, don't you?

Sir George Cayley

[Denti]

As i said above we used to use only wet runway performance data as standard. In fact there was no dry performance data available. The use of said performance was authorized by the relevant authority so it was of course legal to use it that way.

Most probably it was an issue of size since we had to have the performance data for all european airports that a 737 can use on board and we used paper performance tables back then. You can only carry so much documentation in that cramped cockpit.

With our EFBs now of course that is not a problem and we use dry performance data on dry or damp runway and wet performance on damp and wet runway (damp is pilots discretion).

[safetypee]

IIRC many BAe146 operators used wet data only, or at least were encouraged to use wet V1s for every take off; the data was supplied by the manufacturer.
On refection it might have had more to do with a very small V1/Vr speed range (generally low Vrs) and the thickness of the two plastic bugs on the ASI (approx 5 kts); thus the calls became a smooth flow of “V1, Rotate”.

[call100]

What effect would the runway state have on landing? I am beginning to understand the effects on take off. I had always assumed that the dry, damp, wet was more for landing. I take it that this is not the case?

[Intruder]

To start, there is the 15% runway length buffer ("dispatch landing performance") required for a wet-runway landing per FAR 121.195(d):

(d) Unless, based on a showing of actual operating landing techniques on wet runways, a shorter landing distance (but never less than that required by paragraph (b) of this section) has been approved for a specific type and model airplane and included in the Airplane Flight Manual, no person may takeoff a turbojet powered airplane when the appropriate weather reports and forecasts, or a combination thereof, indicate that the runways at the destination airport may be wet or slippery at the estimated time of arrival unless the effective runway length at the destination airport is at least 115 percent of the
runway length required under paragraph (b) of this section.

Then, if the dry runway is of marginal length for the planned landing configuration, a "damp" runway may or may not lead to an overrun or unplanned heavier brake usage. Specific runway, airplane, and operating procedures set up all kinds of permutations...

[Reel Marine]

Dry runway

You are correct in stating that Jar/Faa Ops say that damp has no considerations to be wet under the current rules but they are changing this so use good judgement.