Wet runway - 1.15 factor

[tribo]

Does anyone know how and when the 1.15 factor for wet runway emerged?

[alf5071h]

tribo, I assume that you refer to the 15% differential between the dry 1.67 factor and wet 1.92 factor.

The following notes are taken from a presentation by Transport Canada Aircraft Certification Flight Test,
Titled 'FWP 730 Operational Landing Distances on Dry and Wet Runways for Turbojet Powered Aircraft'

“There is no readily identifiable underlying technical explanation of the operational landing distance factors, which have existed for some time.
The dry factor is believed to have been derived from a statistical analysis of the variables involved as part of the ICAO Final Report of the Standing Committee on Performance. The factors have now become “accepted” as providing a satisfactory safety record”.

Comparative results; calculated vs measured/flight manual “Based on Monte Carlo Statistical Analysis”

"For dry runway the current operational factor of 1.67 for both Destination and Alternate airports appears to be reasonable
For wet runways, without reverse thrust:
1.92 for Destination airport appears to be low
1.67 for Alternate airport appears to be really low
For wet runways, with reverse thrust:
1.92 for Destination airport appears to be marginal
1.67 for Alternate airport appears to be low"

PM for more if required. alf

[tribo]

alf5071h, that is the "correct" 15%.
I have for some time tried to find out how it came into being. I know that the ICAO Airworthiness Committee, Flight Working Group, int the mid 70's were developing guidance material on performance information for wet landing surface definition. From a working paper (AIR C-WP/530, Attachment):

In response to a recent FAA analysis of test of a Caravelle Jet transport and a DBV, and from their own analysis of a Mu-Meter that was tested at the same time the State of France concluded:

1. ....."it seems that the Mu-Meter is too much sensitive at the runway texture to predict the aircraft landing distance on any runways."
2. "The FFA concluding remarks which establishes 'that 15% factor contained in the FAA proposed landing rule change appears to be justified in view of all the tests completed to date' is correct in our point of view." (FAA method based on DBV). (DBV = Diagonal Braked Vehicle)

I suspect that I might be on the right track.
In an other working paper from the ICAO Airworthiness Committee (AIR C-WP/551 dated 29/1/76) there is a figure of calculated stopping distance vs. test stopping distance using SDR MuDRY/MUWET relationships. Tested aircrafts are L-1011, B-737, B-727, DC-9 and Caravelle. In this figure a '15% line' is drawn.
In the working paper there is a reference to a report FAA-FS-160-74-2, August, 1974 with respect to aircraft data reduction. Do you know this report?

[alf5071h]

Sorry [b]tribo[/] I have no other references.
You could start from the following link (possibly a circular reference that I obtained from you). http://www.lima.icao.int/submenu1.as...etprogmenu.asp try 2002, Santa Cruz, 22-27/July

[tribo]

Thanks alf5071h
The link was new to me, but did not help me to get any closer. (But I found other interesting material presented)
I have found some old reports with B-727, DBV and Mu-Meter data from 1971 and DC-9, DBV and Mu-Meter data from 1972. This are preliminary reports from the Joint FAA-USAF-NASA Runway Research Program
From the 1972 report:

Background - .........In 1968, a number of friction measuring vehicles were tested at NASA Wallops Station, Virginia, to ascertain the suitability of the various vehicles for measuring friction in a repetable manner and for providing an index that might be correlated with aircraft stopping performance and/or used to produce information which could be used as an operational guide to pilots during inclement weather conditions. As a result of these and subsequent tests, two ground vehicle measuring methods emerged, each showing promise of correlating with aircraft stopping performance and each showing capability of becoming the basis for an operational technique. The two methods are the NASA diagonal-braked vehicle (DBV) and the British Mu-Meter. Although testing to date has produced data which indicate reasonable correlation may exist between these vehicles and some aircraft, sufficient experimental data has not been obtained to show that such correlation would apply over the range of operational aircraft types and slipperiness conditions likely to be encountered in scheduled air carrier operations.
In order to establish further degree of stopping distance correlation that might be obtained between modern jet transports and ground friction measurement vehicles over a wide range of slipperiness conditions, the FAA, USAF, and NASA are conducting a "Joint FAA-USAF-NASA Runway Research Program"

From the discussion in the report we find that there was a correlation between two DBV vehicles (FAA and NASA) of aproximately +-10%
Further:

The British prefer to show the correlation of aircraft stopping distance with Mu-Meter friction reading under normalized aircraft stopping energy conditions. ..........Boundary lines have been faired through the data obtained under aircraft maximum braking (no reverse thrust) conditions. At a Mu-Meter friction reading of 0.5, the data scatter about a mean point between the boundary lines is approximately +-15%

I do think that I am getting closer to the "source" of the 1.15 factor.
Anybody who can support me on this?