What is a Runway Condition Code (RWYCC)?

Definition

A runway condition code (RWYCC) is a number from 0 to 6 that describes how the runway surface affects aeroplane braking and control. EASA defines it as a number for the runway condition report. The number describes the effect of the surface condition on deceleration performance and lateral control.

ICAO states the purpose in Annex 14. The code lets the flight crew calculate the performance of the aeroplane. The crew takes the code to the performance tables of the aircraft manufacturer.

What each code means

Code 6 is the best and code 0 is the worst. EASA gives the codes in the runway condition assessment matrix (RCAM). The matrix has three parts for each code. They are the surface that the operator sees, the braking that the operator expects, and the braking action that a pilot would report.

The braking and pilot columns are criteria to downgrade a code. They do not set a code by themselves. EASA also gives a short matrix for aerodromes that never report snow and ice. It lists only dry, wet, slippery wet and standing water as surfaces. Codes 4, 1 and 0 have no surface entry there and rest on the braking observation alone.

How to read the three digits

The report gives one digit for each third of the runway. The digits run in the direction seen from the lower runway designator. A pilot hears them as the first, second and third part of the runway in the direction of landing or take-off.

• 6/6/6. The runway is dry, or contamination is 25 per cent or less in every third.
• 5/5/5. Every third is wet or has frost.
• 2/2/2. Every third has standing water or slush of more than 3 mm. EASA uses 5 mm of slush as its example.
• 5/2/2. The first third is wet. The last two thirds have slush deeper than 3 mm.

Each code reflects the runway braking capability for that third. The flight crew derives the stopping distance on approach from it, with the performance data of the aeroplane manufacturer (GM1 ADR.OPS.A.065(a)). The runway condition assessment page covers how the operator works out the code and what the full report adds.

Why 25 per cent and 3 mm

Two limits shape the codes. EASA explains both in GM1 ADR.OPS.B.037(a).

• 25 per cent coverage. A runway counts as contaminated when contamination covers more than a quarter of at least one third. Below that, the crew assumes a dry runway. EASA says tests showed that a dry runway assumption still gives positive stop margins, even if the contamination sits in the worst place.
• 3 mm depth. Below 3 mm, any fluid contaminant can leave the contact area between tyre and runway. It drains away or the tyre presses it into the surface texture. So contamination up to 3 mm should give stopping performance like a wet runway. Above 3 mm, the effect on friction is larger and the codes fall.

Two other inputs matter. Hard contaminants such as ice and compacted snow separate the tyre from the surface at any speed. The temperature limit of -15 °C for compacted snow rests on North American operating practice, and EASA says it may be very conservative.

Some contaminants get no code. These are oil, mud, ash and de-icing chemicals. Their effect varies too much, or there are too few data. Rubber contamination is an exception. In-service data supports an assumption of code 3 for it. A treatment with sand, grit or chemicals gets no credit without verification.

Who assigns the code

The aerodrome operator assigns it. EASA ADR.OPS.B.037 asks the operator to do three things when water, snow, slush, ice or frost is on the runway:

1. Assign a code from the type and depth of the contaminant and the temperature.
2. Inspect the runway when the weather may have changed the surface, and assign a new code.
3. Use special air-reports to trigger a new assessment.

If one third has several contaminants, none above 25 per cent but with a total above 25 per cent, the inspector uses judgment. The inspector picks the contaminant that the aeroplane will most likely meet. This is usually the most widespread one (GM1 ADR.OPS.B.037(b)).

Downgrade and upgrade

The matrix gives the first code. The operator should downgrade it when other information shows lower braking. Examples are vehicle behaviour, shoe scraping, friction readings, local knowledge and special air-reports (AMC1 ADR.OPS.B.037(a) and (b) and GM2 ADR.OPS.B.037(b)).

An upgrade is narrow:

• The operator does not upgrade codes 5, 4, 3 or 2.
• The operator may upgrade code 1 or 0, and not beyond code 3.
• A preponderance of evidence must point to the higher code.
• A friction device must show friction equal to a wet runway (code 5) or better, if it supports the upgrade.
• The operator must assess the surface often while the higher code is in effect.

A special air-report can support an upgrade only together with other information that qualifies. After two consecutive reports of poor braking while code 2 or better is in force, the operator assesses the runway again. After one report of less than poor, the operator assesses again and considers a suspension of operations on the runway (AMC1 ADR.OPS.B.037(c)).

Any changed code carries the word UPGRADED or DOWNGRADED in the remarks.

The FAA RwyCC

The FAA uses the same 0 to 6 scale and writes it RwyCC. The format is X/X/X, for example 4/3/2 (AC 150/5200-30D, 1.12.17). It replaced the Mu values that airport operators reported before.

Four rules differ from the EASA rules:

• The FAA assigns codes only if more than 25 per cent of the overall runway length and width is contaminated. Otherwise it reports contaminant type, depth and coverage for each third without a code (5.4.1).
• The NOTAM system does not accept code 0, because the FAA treats it as an unsafe condition. The system prompts the operator to close the surface (5.4, note).
• The FAA allows an upgrade of code 0 or 1 to code 3 at most. It needs a Mu value of 40 or more on the affected thirds, from a calibrated device (5.4.3.2).
• The FAA splits water and slush depth at 1/8 inch (3.3 mm), where EASA uses 3 mm (5.7.2.1).

Code, friction and braking action

Three different things are easy to mix up.

• The code. A number that the operator derives from the observed contaminant.
• A friction value. A reading from a device on the surface. EASA bans it from the report. EASA says there is no correlation between the readings and aeroplane performance data (GM1 ADR.OPS.A.065(d)). The page on runway friction testing covers the surveys.
• A braking action report. A pilot’s opinion from a landing. The scale runs from good through medium to poor and less than poor.

TarmacView does not assign runway condition codes. The code comes from an inspector who checks the surface, and TarmacView’s pavement analysis is in development.