Historical wet runway performance data

[tcasblue]

Hi,

I have been reading up on wet runway performance data recently and am interested in some historical data concerning the FAA regulations/NTSB recommendations only. As you may know the wet runway performance is considered as advisory only. As far as I now, it is/or was not considered to be mandatory to provide this information, and unlike the dry runway performance numbers, does not have to be flight tested and apparently is usually not flight tested due the difficulty of getting proper test conditions.

Things started to change from a recommended and regulatory point of view after a Southwest airlines overrun at Chicago in 2007. Prior to this accident, was there any regulatory requirement for the landing distance of a wet runway to be equal to what the published wet runway data stated was the required landing distance or was the only actual legal requirement that the dry runway distance be met regardless of runway conditions.

[Mad (Flt) Scientist]

Right now, today, in part 25 there is no requirement to produce anything other than dry landing data. (My emphasis):

25.125(c) For landplanes and amphibians, the landing distance on land must be determined on a level, smooth, dry, hard-surfaced runway.

You won't find any reference to wet runway in connection with landing, though it occurs repeatedly in connection to takeoff data nd accelerate-stop data in particular.

The OLD which is operationally used (soon to be mandated) (after TALPA, after Midway) has no regulatory basis in part 25.

[safetypee]

An excellent historical view was prepared for ICAO and in part published as a ‘Circular 329 AN191 Runway Surface Condition Assessment, Measurement and Reporting’. This identified the need for factored landing distances based on research by NASA and RAE, generally associated with larger jet transport aircraft operating from concrete runways (circa 1960s). The information is incorporated into recent requirements for reporting runway conditions, where those reports, to be heed by crews, effect aircraft performance.

CFR 121-195 is the legal mandate for landing on wet runways “… 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.”
An acceptable means of compliance is in the AC, but this may have be superseded by manufacturers data based on Operational Landing Performance (OLD).
https://www.faa.gov/documentLibrary/media/Advisory_Circular/121.195-1A.pdf

EASA has similar requirements, but specifically mandates a pre-landing assessment.
Although wet landing data is based on factorised dry data, crews are still required to assess and take account of all aspects when landing on wet runways.
Another EASA difference is in the certification requirements for contaminated operations; although not specifically referring to ‘wet’, the information provides good background for the residual risks and assumptions made in determining landing performance. Also consider that there is little difference between a wet runway (2.95mm) and a contaminated one (3mm) water.

Noting that ‘Southwest Airlines Flight 1248’ involved a snow contaminated runway.

Operating in adverse conditions on the basis of being legal or not, or ‘only advisory’, is opens opportunity for misjudgement or ill chosen course of action.
Better advisory ‘advice’ is in CS 25 - AMC 25.1591 The derivation and methodology of performance information for use when taking-off and landing with contaminated runway surface conditions. ~ page 877 onwards;
“Operation on runways contaminated with water, slush, snow, ice or other contaminants implies uncertainties with regard to runway friction and contaminant drag and therefore to the achievable performance and control of the aeroplane during take-off, since the actual conditions may not completely match the assumptions on which the performance information is based. Where possible, every effort should be made to ensure that the runway surface is cleared of any significant contamination.
https://www.easa.europa.eu/sites/default/files/dfu/CS-25%20Amendment%2023.pdf

https://safetyfirst.airbus.com/landing-on-contaminated-runways/