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coefficients as a function of tire pressure and groundspeed in combination with an anti-skid
efficiency. The ESDU data used represented runways with grooved or open macro-texture/PFC
runways with texture depths between 0.5 and 2.5 mm. An evaluation of the ESDU data for these
runways shows that for a texture depth midway between the above limits in combination with
typical anti-skid efficiencies, stopping performance is approximately the same as using 70% of the
dry runway braking capability.
The previous definitions of a dry runway and wet runway (see above) were clearly not applicable
anymore and where removed from ACJ 25X1591. Additionally performance information for
grooved/PFC runways derived according to JAR 25 Change 15 / FAR 25 Amendment 92 must be
accompanied by a note limiting its use to grooved/PFC runways that have been constructed and
maintained to meet the friction level qualifications in FAA-AC 150/5320-12C or its equivalent.
JAR-OPS
JAR-OPS 1.520 requires that an operator shall ensure that when the appropriate weather reports or
forecasts, or a combination thereof, indicate that the runway at the estimated time of arrival may
According to a CAA-UK paper on the derivation of the landing distance factor, the origin of the
dispatch factors are believed to be the ‘traditional’ 1.43 factor with an allowance for runway surface
variations to bring it to 1.67. As a result of testing of jet aircraft on wet surfaces, the 1.67 factor was
found to be inadequate resulting in the additional 1.15 factor for operations on wet runways.
be
wet, the landing distance available is at least 115% of the required landing distance, determined in
accordance with JAR–OPS 1.515 (dry runways). JAR-OPS 1.520 allows a landing distance on a wet
runway shorter than that required above, but not less than that required for a dry runway, provided
that the Aeroplane Flight Manual includes specific additional information about landing distances on
wet runways. This information will have to be derived from flight testing.
The definitions of runway state as defined in JAR-OPS 1.480 are a direct result of the original
definitions defined in JAR 25 Change 13. With the advent of NPA 25BDG-244 changes in JAR 25 were
not reflected in changes in JAR-OPS however. This is being addressed by the JAA Performance
Subcommittee and covered in DNPA-OPS 47, which is still awaiting further progress by EASA. The
accompanying Regulatory Impact Assessment (RIA) states that the current definition of a dry runway
was written when the understanding of the braking characteristics of aircraft on grooved and PFC
runways was in its infancy. Since then, knowledge of the subject has evolved considerably,
principally following the development of NPA 25BDG-244 to the extent that it is now recognised that
grooved or PFC runways do not retain effectively dry braking action when wet.
The following definitions of dry and wet runway are contained in DNPA-OPS 47:
Dry runway: A dry runway is one which is clear of contaminants and visible moisture within the
required length and the width being used.
Wet runway: A runway that is neither dry nor contaminated is considered wet.
Runway Maintenance Standards
Runway maintenance standards can be found in ICAO Annex 14 and the ICAO Airport Services
Manual. Attachment A of ICAO Annex 14 contains minimum friction values for different friction
testing devices (self-wetting maintenance friction measurements) for three categories: The Design
Objective Level (DOL) for new runways, the Maintenance Planning Level (MPL) and the Minimum
Friction Level (MFL). When the measured friction level drops below the MFL a NOTAM ‘slippery
when wet’ has to be furnished.
According to the Airport Services Manual the term Minimum Friction Level is related to ensuring the
safe operation of aeroplanes when the runway is wet. Appendix 1 to the Airport Services Manual
contains a method for relating the MFL to aeroplane wet dispatch performance.
In other words runways maintained in accordance with the guidelines provided by the Airport
Services Manual should ensure safe operations for aeroplanes provided wet
Friction Measurements & Aircraft Performance
dispatch performance is
applied and provided the runway measured friction is above MFL. When the maintenance friction
measurements drop below the MFL, clearly application of wet takeoff and landing performance
regulations may be inappropriate for field length limited operations. Other comparable maintenance
standards can be found in FAA AC 150/5320-12C and CAA-UK CAP 683.
Maximum wet runway friction drops with increasing groundspeed and for low speeds approximates
the dry value which is virtually independent of groundspeed. This is also reflected in the certification
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