Cracking the Code: Understanding Runway Condition Codes

by TCCA GRF Implementation Team: Guy Héneault, Drew Dutton, Robert Kostecka, Cheryl Bugden, Aerodrome Standards, and Benoit Saulnier, Commercial Flight Standards

Runway Condition Codes (RWYCCs) are one of the features of the Global Reporting Format (GRF) for runway surface conditions. Although these RWYCCs are quite familiar to many pilots operating transport category jet aeroplanes—and have been used for making time of arrival landing performance assessments for more than a decade—they may be quite new to many other pilots. This article will discuss what RWYCCs are, how they were developed and the important safety information that they convey. Most importantly, it will explain how RWYCCs can be used to help pilots address the hazards and risks associated with landings on wet and contaminated runways.

Essentially, the RWYCC is a number, from 0 to 6, which represents the slipperiness of a specific third of a runway and provides a standardized “shorthand” for reporting this information. A RWYCC of 0 corresponds to an extremely slippery runway and 6 corresponds to a dry runway. RWYCCs also serve to enhance all pilots’ situational awareness of where the slipperiest runway conditions and contaminants are located on a runway, and they can be used by pilots to make a time of arrival landing performance assessment (for those aeroplanes with suitable performance information).

RWYCCs are included in a Runway Surface Condition (RSC) NOTAM, when runway surface conditions are reported in thirds (e.g., 3/3/2). Reporting in thirds typically occurs on longer runways used by larger, high performance aeroplanes and is only available for paved runways. The decision whether or not to report by runway thirds or by full runway length is made by the airport or aerodrome operators in consultation with the operators that utilize the facility.

When reporting the runway surface condition information in thirds, the RSC NOTAM for an individual runway will include two reports: one for each runway direction (e.g., RSC RWY 07 and RSC RWY 25). The RWYCCs are presented in the direction of flight for each runway direction to help pilots to visualize where the contaminants are located on the runway. For example:

RSC RWY 07 3/3/5…

RSC RWY 25 5/3/3…

The photograph below illustrates how reporting in thirds helps to improve pilot situational awareness.

The photograph illustrates how reporting in thirds helps to improve pilot situational awareness.

Credit: Ron Tidy

The two dashed blue lines overlaid on the photo help to show benefits of reporting runway surface conditions by thirds with associated RWYCCs. For landings in this direction, the RWYCCs would be 3/3/5. This “shorthand” description of runway friction makes it easy for pilots to understand that the contaminants are primarily located in the first two thirds of the runway. For landings in the opposite direction, the RWYCCs would be 5/3/3.

 

To understand how RWYCCs are determined, one first needs to look at the Runway Condition Assessment Matrix (RCAM). The RCAM is a tool that maps the equivalency between standard runway surface descriptions, RWYCCs, braking action reports, and aircraft performance information (data). It is used to harmonize airport observations with time of landing performance assessments made by the flight crew, providing a significant advancement over the previous performance methods and practices.

The RCAM was originally developed by the Takeoff and Landing Performance Assessment Aviation Rulemaking Committee (TALPA ARC), whose work ultimately resulted in GRF. (For more information about the TALPA ARC, please see Canada Adopts New Global Reporting Format for Runway Surface Conditions, also in this issue of the ASL.)

The RCAM effectively serves as the cornerstone of GRF. With the RCAM, we now have a powerful tool that integrates the safety benefits from TALPA—and puts all the pieces of the puzzle together:

  • Aerodrome Operators: With the implementation of GRF, airport and aerodrome operators will now report runway surface conditions in accordance with a standardized format that utilizes standardized, globally accepted terminology. This reporting is now integrated with airplane performance information that is used by flight crews.
  • Aeroplane Performance Information: For the last decade, the major manufacturers of transport category aeroplanes have been producing performance information that is based on the TALPA methods that form the basis of GRF; these methods utilize operationally representative landing distances—which is a significant advancement. For aeroplanes that do not have manufacturer-supplied TALPA-based performance information or performance information developed by a third party, a Landing Distance Factors Table is now available in Advisory Circular (AC) 700-057, Table 6.
  • Flight Crews: With the introduction of GRF, flight crews will now receive benefit from standardized runway surface conditions, which is presented in a format that harmonizes with the performance information used to make time-of-arrival landing performance assessments.

Essentially, the RCAM (shown below) consists of two major portions:

  • Assessment Criteria, which appear on the left (unshaded) half of the RCAM; and
  • Control/Braking Assessment Criteria, which appear on the right (shaded) half of the RCAM. (Downgrade Assessment Criteria is the equivalent term used in the RCAM for airport and aerodrome operators).
Table 1. The Runway Condition Assessment Matrix (RCAM) used by flight operations personnel. (The version used by airport and aerodrome operators is similar; it has minor differences and also includes additional information.)
Assessment Criteria Control/Braking Assessment Criteria
Runway Surface Description RWYCC Vehicle Deceleration or
Directional Control Observation
Pilot Braking Action
  • Dry
6 n/a not applicable n/a not applicable
  • Frost
  • Wet (The runway surface is covered by any visible dampness or water up to and including 1/8 inch (3 mm) depth)

Up to and including 1/8 inch (3 mm) depth:

  • Slush
  • Dry Snow
  • Wet Snow
5 Braking deceleration is normal for the wheel braking applied and directional control is normal Good

-15°C and colder outside air temperature

  • Compacted Snow
4 Braking deceleration or directional control is between Good and Medium Good to Medium
  • Slippery When Wet (wet runway)
  • Dry Snow or Wet Snow (Any depth) On Top Of Compacted Snow

Greater than 1/8 inch (3 mm) depth:

  • Dry Snow
  • Wet Snow

Warmer than -15°C outside air temperature:

  • Compacted Snow
3 Braking deceleration is noticeably reduced for the wheel braking effort applied or directional control is noticeably reduced Medium

Greater than 1/8 inch (3 mm) depth:

  • Standing Water
  • Slush
2 Braking deceleration or directional control is between Medium and Poor Medium to Poor
  • Ice
1 Braking deceleration is significantly reduced for the wheel braking effort applied or directional control is significantly reduced Poor
  • Wet Ice
  • Slush On Top Of Ice
  • Water On Top Of Compacted Snow
  • Dry Snow or Wet Snow On Top Of Ice
0 Braking deceleration is minimal to non-existent for the wheel braking effort applied or directional control is uncertain Poor / Nil

The Assessment Criteria (left unshaded half of RCAM) includes runway surface descriptions and RWYCCs. The runway surface descriptions are categorized based on the type and depth of contaminant (temperature is also considered for compacted snow); these are arranged hierarchically—in order of how “slippery” they are. DRY—which has the most friction—is at the top of the list, and conditions like WET ICE—which have the least friction—are at the bottom. Each runway surface description has a corresponding RWYCC. For example, 1 in. of dry snow (listed on the RCAM as Greater than 1/8 in. (3 mm) depth) has a corresponding preliminary RWYCC of 3. (An explanation of how preliminary RWYCCs are later confirmed, downgraded or upgraded, appears below.) RWYCCs are determined by the airport or aerodrome operator and provide pilots with a reasonably conservative estimate of the aircraft’s landing performance.

Under some conditions, the runway surface may be more slippery than the preliminary RWYCC determined by referencing the runway surface descriptions in the RCAM. Especially at temperatures near and above freezing (i.e., at -3°C and warmer), the runway surface condition may be more slippery than indicated by the preliminary RWYCC. At these temperatures, airport and aerodrome operators should exercise vigilance and downgrade the RWYCC, if appropriate. In addition, any process that transfers heat to the surface may make the runway more slippery; possible heat sources include: an aircraft’s tires, engine exhaust/thrust reverse, atmospheric conditions, and precipitation. Runway treatments can also temporarily result in more slippery conditions.

The Control/Braking Assessment Criteria (right shaded half of RCAM) provides the criteria that the airport and aerodrome operators use to determine if the RWYCC accurately reflects the slipperiness of the runway. The Control/Braking Assessment Criteria on the version of RCAM used by flight crews includes: Pilot Braking Action and Vehicle Deceleration or Directional Control Observations. (The RCAM version used by airport and aerodrome operators is similar and also includes CRFI information.)

The airport or aerodrome operator should determine whether the preliminary RWYCCs accurately reflect the runway conditions. Through this determination, which should consider CRFI (if available), vehicle deceleration or directional control observations, pilot braking action report(s), local knowledge and/or other information, the preliminary RWYCCs will then be: confirmed; downgraded; or upgraded (providing additional stringent criteria are met). This RWYCC is then published in the RSC NOTAM.

To see how this works, consider the previous example, where it was shown that 1 in. of dry snow (listed on the RCAM as “Greater than 1/8 in. (3 mm)”), had a corresponding preliminary RWYCC of 3. A reliable braking action report of Poor braking would likely lead the airport or aerodrome operator to downgrade the RWYCC to 1. This is illustrated on the next page.

Table 2. 1 in. of dry snow (listed on the RCAM as “Greater than 1/8 in. (3 mm)”), had a corresponding preliminary RWYCC of 3. A reliable braking action report of Poor braking would likely lead the airport or aerodrome operator to downgrade the RWYCC to 1. This RWYCC will be published in the RSC NOTAM.
Assessment Criteria Control/Braking Assessment Criteria
Runway Surface Description RWYCC Vehicle Deceleration or
Directional Control Observation
Pilot Braking Action
  • Dry
6 n/a not applicable n/a not applicable
  • Frost
  • Wet (The runway surface is covered by any visible dampness or water up to and including 1/8 inch (3 mm) depth)

Up to and including 1/8 inch (3 mm) depth:

  • Slush
  • Dry Snow
  • Wet Snow
5 Braking deceleration is normal for the wheel braking applied and directional control is normal Good

-15°C and colder outside air temperature

  • Compacted Snow
4 Braking deceleration or directional control is between Good and Medium Good to Medium
  • Slippery When Wet (wet runway)
  • Dry Snow or Wet Snow (Any depth) On Top Of Compacted Snow

Greater than 1/8 inch (3 mm) depth:

  • Dry Snow
  • Wet Snow

Warmer than -15°C outside air temperature:

  • Compacted Snow
3 Braking deceleration is noticeably reduced for the wheel braking effort applied or directional control is noticeably reduced Medium

Greater than 1/8 inch (3 mm) depth:

  • Standing Water
  • Slush
2 Braking deceleration or directional control is between Medium and Poor Medium to Poor
  • Ice
1 Braking deceleration is significantly reduced for the wheel braking effort applied or directional control is significantly reduced Poor
  • Wet Ice
  • Slush On Top Of Ice
  • Water On Top Of Compacted Snow
  • Dry Snow or Wet Snow On Top Of Ice
0 Braking deceleration is minimal to non-existent for the wheel braking effort applied or directional control is uncertain Less than Poor / Nil

The job of the airport or aerodrome operator is to accurately report the runway surface conditions; essentially, just to “report the news.” Determining how this information is to be used is the responsibility of flight operations personnel. Here again, RWYCCs and the RCAM play an important role.

The RCAM can be used by flight crews to make their time-of-arrival landing performance assessments using data that more accurately represents actual aircraft braking performance. For example, consider a situation where an RSC NOTAM includes RWYCCs of 4/4/3. In this case, many operators will direct their flight crews to base their landing performance assessment on the most conservative RWYCC (in this case 3—which corresponds to Medium braking). If the aircraft subsequently receives a reliable braking action report of Poor, the flight crew may use this as the basis for their landing performance assessment.

Note: The examples above highlight an important distinction: RWYCCs—which are determined by the airport or aerodrome operator—use numbers (0 to 6) to describe how slippery the runway is; while braking action reports from pilots use words such as Good, Medium, Poor and NIL.

Flight crews can also use the RCAM to help them mitigate the hazards and risks associated with landing on runways that are wet or contaminated with standing water. The guidance in AC 700-057, Appendix C, warns that due to the challenges of reporting water on a runway—especially during a dynamic event like a thunderstorm—these conditions may not always be reported, or it may not be possible to report them in a timely manner. For example, consider a situation where an RSC NOTAM reports wet runway conditions with corresponding RWYCCs of 5/5/5. AC 700-057 recommends that, due to the risk of standing water, prior to initiating an approach, pilots should verify that the aircraft can stop within the Landing Distance Available using an RWYCC of “2” (corresponding to Medium to Poor braking), whenever there is the likelihood of:

  • moderate or greater rainfall on a smooth runway; or
  • heavy rain on a grooved/porous friction course (PFC) runway.
Table 3. During a rainfall event, an RSC NOTAM may report wet runway conditions with corresponding RWYCCs of 5/5/5. Prior to initiating an approach, pilots should verify that the aircraft can stop within the Landing Distance Available using an RWYCC of “2” (corresponding to Medium to Poor braking), whenever there is the likelihood of: moderate or greater rainfall on a smooth runway; or heavy rain on a grooved/PFC runway.
Assessment Criteria Control/Braking Assessment Criteria
Runway Surface Description RWYCC Vehicle Deceleration or
Directional Control Observation
Pilot Braking Action
  • Dry
6 n/a not applicable n/a not applicable
  • Frost
  • Wet (The runway surface is covered by any visible dampness or water up to and including 1/8 inch (3 mm) depth)

Up to and including 1/8 inch (3 mm) depth:

  • Slush
  • Dry Snow
  • Wet Snow
5 Braking deceleration is normal for the wheel braking applied and directional control is normal Good

-15°C and colder outside air temperature

  • Compacted Snow
4 Braking deceleration or directional control is between Good and Medium Good to Medium
  • Slippery When Wet (wet runway)
  • Dry Snow or Wet Snow (Any depth) On Top Of Compacted Snow

Greater than 1/8 inch (3 mm) depth:

  • Dry Snow
  • Wet Snow

Warmer than -15°C outside air temperature:

  • Compacted Snow
3 Braking deceleration is noticeably reduced for the wheel braking effort applied or directional control is noticeably reduced Medium

Greater than 1/8 inch (3 mm) depth:

  • Standing Water
  • Slush
2 Braking deceleration or directional control is between Medium and Poor Medium to Poor
  • Ice
1 Braking deceleration is significantly reduced for the wheel braking effort applied or directional control is significantly reduced Poor
  • Wet Ice
  • Slush On Top Of Ice
  • Water On Top Of Compacted Snow
  • Dry Snow or Wet Snow On Top Of Ice
0 Braking deceleration is minimal to non-existent for the wheel braking effort applied or directional control is uncertain Poor / Nil

Conclusion

RWYCCs have been designed to be a simple and effective means of enhancing pilot situational awareness by clearly and concisely indicating how slippery the various sections of a runway are. In addition, they provide a significant safety advancement since they align with aeroplane performance data (information) that can be used for the time-of-arrival landing performance assessment.

A great deal of thought and research by industry experts has gone into the development of RWYCCs and the RCAM; these are powerful tools that are intended to help mitigate the hazards and risks associated with landings on wet and contaminated runways.

Further information and guidance

Guidance on RWYCCs is available for flight operations personnel and for airport and aerodrome operators: