3-9 Note 1: AFM guidance may contain additional limitations for contamination type and depth due to possible damage to the airframe from the impingement of the contamination.
Note 2: During landing, it is possible that loose contaminant can aid in deceleration. However, it is recommended that credit not be taken for this effect.
Note 3: Loose contamination that affects aircraft acceleration has been referred to by some operators as “clutter.” It is recommended that terminology used by operators be harmonized with the guidance in ASTM E3188, as well as this AC, AC 25-32, and AC 150/5200-30.
3.13.4 L anding Performance. Landing performance is most affected by the degree mechanical wheel braking can impart a decelerating force to the aircraft. This effect is classified using a standardized engineering scale that represents the maximum force available from an aircraft’s wheel braking system. A model was created by the TALPA ARC to create a reasonably conservative relationship between this engineering scale and a set of standardized descriptions of wet and contaminated conditions known as the RCAM.
3.13.5 RCAM. The RCAM serves three core functions. First, it provides standardized means of reporting information from aircraft and airports so that a TOA landing performance assessment can be made. Second, it is a means of classifying information so that aircrews can build a shared mental model of the expected degree of risk during landing. Third, it is a means for airports and aircraft manufacturers to develop standardized models for calculating performance. It is important to understand that the RCAM is at its core, a model for risk management.
3.13.5.1 Mo dels vs Theories. Models are designed to provide an effective path for communication. Theories are designed to provide an explanation for all data involved in a process. The RCAM was designed to provide a reasonably conservative model for runway conditions and engineering-based wheel braking performance values. The RCAM is an industry best practice.
However, there may be instances where the model may not apply values conservative enough for TOA landing assessments. The use of braking action reports along with the knowledge and skills outlined in this AC are designed to assist in mitigating these instances.
3.13.5.2 Standardized Reporting. TOA assessments should be conducted as the result of an airport observation and/or aircraft observations. Dry conditions are not normally reported, unless they occur in conjunction with other parts of the runway that are other than dry. Observations from airports are given with numerals (e.g., 5, 3, 2, etc.) while observations from aircraft are given with words (e.g., Good, Medium, etc.).
3.13.5.3 Aircraft Braking Performance Levels. The RCAM is divided into six categories, each representing a range of maximum wheel braking ability.
Operator guidance should contain landing performance data for each category
3-10 that represents the lowest inclusive value of wheel braking for that category.
TOA landing assessments normally use only one category. However, multiple reports may be provided for each runway as described below.
3.13.5.4 Reporting Runway Sections. RwyCCs are provided for each third of the runway. This was primarily done to provide flightcrews with situational awareness. Airports are tasked with maintaining consistent runway conditions throughout their entire length. However, weather and operational conditions may result in variations. Operators should establish policies regarding how TOA landing assessments are made when varying RwyCCs are reported.
3.13.5.5 Building a Mental Model of Risk. The ability to discriminate airport observations, aircraft observations, and cockpit observations (e.g., radar, visual cues, etc.) allows the flightcrew to build a shared mental picture of what the most likely condition a flightcrew can expect at the TOA. In general terms, with conditions constant and timely reporting, braking action reports may offer a higher degree of confidence than RwyCCs. Similarly, onboard radar may offer a timelier picture of expected conditions than either braking action reports or RwyCCs. Flightcrew training and operational guidance is key to effectively mitigating this risk.
3.13.5.6 Standardized Performance Metrics. There are three RCAMs published that provide performance metrics for stakeholders. The RCAM in this AC is intended to be used by flightcrews and aircraft operators. AC 150-5200/30 contains an RCAM for airport operators that includes guidance for runway friction measurements. AC 25-32 contains an RCAM with engineering values used to calculate landing distances referencing certification standards. This guidance for airports and manufacturers ensures that the information in the RCAM depicted here represents the best available information for operators and flightcrews.
Note: Runway friction measurements utilized by airports do not have the appropriate degree of precision and accuracy to be used for TOA landing assessments and are purposely omitted from this AC.
3.13.5.7 Control/Braking Assessment Criteria. Table 3-2 lists the basi c metrics for how vehicle control can be related to braking assessments. This information is generic throughout all RCAM types and can be applied to any vehicle used to observe wheel braking. Guidance for reliable aircraft braking action reports is covered in Chapter 4 and should be used by all operators reporting aircraft observations, either by pilots or aircraft reporting systems.
3-11 Table 3-2. Pilot/Operator Runway Condition Assessment Matrix (RCAM) Assessment Criteria Control/Braking Assessment Criteria Runway Condition Description RwyCC Deceleration or Directional Control Observation Reported Braking Action
• Dry 6 --- ---
• Frost
• Wet (includes damp and 1/8 inch depth or less of water) 1/8 Inch (3 mm) Depth or Less of:
• Slush
• Dry Snow
• Wet Snow 5 Braking deceleration is normal for the wheel braking effort applied AND directional control is normal.
Good -15 ºC 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) over Compacted Snow Greater Than 1/8 Inch (3 mm) Depth of:
• Dry Snow
• Wet Snow Warmer Than -15 ºC 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 of:
• 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 over Ice
• Water over Compacted Snow
• Dry Snow or Wet Snow over Ice 0 Braking deceleration is minimal to nonexistent for the wheel braking effort applied OR directional control is uncertain.
Nil
3-12 Note 1: The unshaded portion of the RCAM (“Assessment Criteria” columns) is used by airport operators conducting a runway condition assessment.
Note 2: The shaded portion of the RCAM (“Control/Braking Assessment Criteria” columns) is for pilots making braking action reports.
Note 3: Runway condition codes (RwyCC), one for each third of the landing surface (e.g., 4/3/3), represent the runway condition description as reported by the airport operator.
4-1 CHAPTER 4. BRAKING ACTION REPORTS
4.1 General. Standardizing braking action reports by using braking action codes in the RCAM, which provides the latest PIREPs, ensures that pilots are provided objective, useful information so they can accurately assess the runway condition prior to landing. A runway is assumed to be dry unless reported otherwise (usually through the Automatic Terminal Information Service (ATIS), NOTAM, or PIREP). Runway conditions other than dry are described as being either wet or contaminated. Since aircraft braking ability varies greatly due to wet or contaminated runway conditions, it is important to report any reduction in braking ability to air traffic control (ATC).
4.2 Understanding Aircraft Deceleration. The “stopping performance” of a landing aircraft is a combination of aerodynamic and mechanical braking forces. The relative impact of these forces changes during the landing rollout. Aerodynamic forces are dominant immediately after touchdown when the aircraft is at higher speeds. As the aircraft decelerates, mechanical forces play a more important role.
4.3 Classifying Wheel Braking Action. Braking action describes the degree to which the weight on the braked wheels can be transferred into a decelerating force by the aircraft’s brakes. This system is comprised of the tire, wheel brakes, and anti-skid system (if available). Usually, as brakes are applied, the wheel speed decreases below the free rolling speed and a wheel slip is created. The friction created by this wheel slip imparts a decelerating force to the aircraft. Anti-skid systems modulate the wheel braking to ensure a targeted wheel slip value is not exceeded. On a dry runway, the ability of the wheel brakes to impart a decelerating force is normally limited to the ability of the braking system to absorb heat and is said to be “torque limited.” As the runway friction decreases, this slip ratio will be achieved at successively lower forces applied to the wheel brakes and the force imparted by the brakes will be limited by the anti-skid. In this case, the brakes are said to be “friction limited.” The relationship between the decelerating force from the braked wheels and the vertical force acting on them is known as the wheel braking coefficient. As the runway becomes more slippery, the wheel braking coefficient decreases. The standardized scale used in the RCAM is based on wheel braking performance and has three distinct characteristics:
1. The scale only represents values when the aircraft’s braking system is performing at its maximum capability (i.e., the point of friction-limited deceleration is reached due to the slipperiness of the runway);
2. Each division of the scale represents a range of values with the defining value for that division being the lowest wheel braking coefficient value for that range; and
3. The scale assumes the braking coefficient value (reported braking action) is valid for the entire length of the landing roll, unless otherwise specified. (See paragraph 4.10 below.)
4.4 Braking Action Reports. Braking action is an observation of the aircraft’s performance when the maximum capability of the wheel brakes is being applied. The report provides time-critical and operationally relevant information to pilots when a runway may be more
4-2 slippery than previously reported. In addition to pilots, braking action reports can be used by airport operators to confirm or downgrade a RwyCC in an updated Field Condition Report (FICON) NOTAM.
4.4.1 B raking Action. “Braking action” is the term used to describe the maximum capability of a vehicle’s braking system on a wet or contaminated surface with reference to the standardized scale in the RCAM under the column labeled “Control/Braking Assessment Criteria.” A braking action report may also convey the observation by the flightcrew that the reported wheel braking performance that is likely to be experienced during the landing rollout. Braking action is classified according to the primary source of information used to generate the report:
1. P ilot Braking Action Report (PBAR): A braking action report resulting from the observations of a pilot of the aircraft’s autobraking system’s ability to prevent skidding or locking up of the wheels which causes the aircraft to skid (refer to https://www.youtube.com/watch?v=Q8PBHLJfztw).
2. Aircraft Braking Action Report (ABAR): A report given describing a level of braking action using data from the aircraft.
4.4.2 R eliable PBAR. To determine if a braking action report is reliable, consider the type of aircraft making the report and the timeliness of the report. A report recently made by an aircraft similar to the one you are flying is more likely to provide information you can use to accurately predict your aircraft’s braking performance.
4.5 “B raking Action Advisories A re in Effect.” If runway braking action is reported as less than good, or if weather conditions are conducive to deteriorating braking action, ATIS will include the statement, “Braking action advisories are in effect.” When this happens, ATC is required to provide each arriving and departing aircraft with the most recent braking action report for the runway in use. As a pilot, when braking action advisories are in effect, it is your responsibility to ensure that you have the most recent braking action report from ATC. You should also be prepared to provide ATC with a report after landing describing the runway conditions you observed and your aircraft’s braking ability.
4.5.1 B raking Action Degraded. When stopping an aircraft, the pilot expects the deceleration of the aircraft to be proportional to the amount of braking applied. When the actual deceleration is less than expected, braking action is degraded. Usually, as brakes are applied, the wheels slow and the friction between the tires and the runway surface causes the aircraft to decelerate. If contaminants such as water, snow, slush, or ice are present on the runway, even if the wheels start to slow down as brakes are applied, the tires may slip along the surface of the runway due to the lack of friction caused by the presence of the contaminant(s). If you notice a deterioration of braking action which is worse than reported, you should report it to ATC to alert other pilots to the condition.
4.5.2 RCAM. The RCAM is the tool that enables airport operators and aircraft pilots to accurately communicate runway conditions. The RCAM ties runway contaminant types
4-3 and depths to aircraft performance. Pilots need to be familiar with the RCAM in order to make objective braking action reports that are useable to other pilots.
4.6 How to Use the RCAM.
4.6.1 Format. The RCAM braking action codes and definitions are shown in Table 3-2, Pilot/Operator Runway Condition Assessment Matrix (RCAM). Note that the left side of t he table, labeled “Assessment Criteria,” is for use by airport operators that conduct and report the runway condition of paved runways. Airport operators report RwyCCs as numbers (e.g., 5, 3, 2, etc.). RwyCCs are not reported by pilots. Pilots should use the right side of the table, labeled “Control/Braking Assessment Criteria,” to make braking action reports and should use words such as “good,” “medium,” or “poor.” Dry conditions are not normally reported unless other parts of the runway are wet or contaminated.
4.6.2 A ircraft Braking Performance Levels . The matrix is divided into six categories, each representing a range of maximum wheel braking ability. Operator guidance should contain landing performance data for each category that represents the lowest inclusive value of wheel braking for that category. Multiple reports may be provided for each runway, as described below.
4.6.2.1 R eporting Runway Sections. RwyCCs are provided for each third of the runway. This is primarily done to provide pilots with situational awareness.
Airport operators are tasked with maintaining consistent runway conditions throughout their entire length; however, weather and operational conditions may result in variations.
4.6.2.2 Control/Braking Assessment Criteria. The RCAM lists the basic metrics for how vehicle control can be related to braking assessments. This information can be applied to any vehicle used to observe wheel braking.
4.7 Criteria for Making Observations. Braking action reports should be based solely on the wheel braking component of the aircraft’s deceleration. Pilots need to understand that stopping results do not necessarily correlate to braking action. The effects of aerodynamic forces, while beneficial to stopping performance, should not be considered when making a braking action report. For turbojets, the effect of reverse thrust should not be considered. Likewise, for propeller driven airplanes, the effect of reverse pitch should not be considered.
4.7.1 C onsiderations. To make an accurate assessment of the airplane’s braking performance, whether the braking action report is based on pilot’s observations (PBAR) or aircraft data (ABAR), the following questions need to be considered:
1. Wh at was the level of braking performance in relation to the scale in the RCAM? For aircraft with little or no direct instrumentation on wheel braking forces, pilots should determine the level of braking through observation. (See paragraph 4.9 below.) For
4-4 aircraft with ABAR systems installed, the system may automatically identify if braking is friction limited and will determine the RCAM level of braking.
2. Was it possible to detect wheel braking during the aircraft’s deceleration on the runway? Confirm that wheel braking can be readily distinguished by applying brakes to the point where a change in deceleration can be identified. This change in deceleration should be easily discernable during manual braking by noting the effect of increasing brake application on deceleration. It may also be discernable while using autobrakes if the aircraft manufacturer or operator has developed appropriate procedures for this purpose.
3. Was the runway condition such that the observed braking action could reasonably be expected throughout the entire landing rollout? If you determine that runway conditions are not consistent throughout the entire runway, that information should be indicated in the braking action report.
4. Did the aircraft’s braking system reach the point where it was friction limited?
Identify when friction-limited braking occurs by observing the point where an increase in brake activation yields no increase in deceleration.
Note 1: In case of landing in non-normal conditions, ABAR/PBAR may not be applicable, since the aircraft may not have its normal braking capability.
Note 2: The primary focus during landing is a safe stop and lateral control.
4.8 Recommended Method for Classifying Pilot Observations. The following information is applicable to PBARs based on the observations made by a pilot without any reference to aircraft data. It utilizes industry best practices to provide observational references for the braking levels listed.
4.8.1 T erminology . Given that autobrake use is an SOP in most large jets, the criteria that can be observed when applying brakes manually, to maximize the usefulness of PBARs, should be the use of the terms “good,” “medium,” “poor,” and “nil.” (See Figure 4-1, An Illustration of Good, Medium, and Poor Braking, below.) These terms allow a pilot with little or no flight deck instrumentation on braking to report significant ranges of deceleration performance. The criteria for these reporting terms are described below:
4.8.1.1 G ood. Describes the level of braking typically seen on a wet runway when aggressive braking can still be achieved, and directional control is not significantly compromised. For this level of deceleration performance, the initiation of friction-limited braking may not be required as aggressive braking can be reasonably inferred.
4.8.1.2 Medium. Describes the level of braking typically seen on snow-covered runways. Wheel braking forces can still be differentiated, and their effectiveness controlled, but at a noticeably reduced level. Friction-limited braking is readily identified as the point where brake pedal commands cease to increase deceleration or when anti-skid braking becomes active. Directional control is noticeably reduced.
4-5
4.8.1.3 Poor. Describes the level of braking typically seen on ice-covered runways or when hydroplaning during heavy rain. Braking and directional control is minimal and an increase in brake application fails to produce any increase in deceleration. Poor braking is considered a hazardous condition, as small errors in aircraft configuration and technique can result in excessive deviations in landing performance.
4.8.1.4 Nil. Braking deceleration is minimal to non-existent or directional control is uncertain. A report of nil braking action on a runway requires the closure of that runway for safety reasons. Although closing the runway may be an inconvenience to other pilots, pilots that experience nil braking action should be encouraged to make such reports.
Note: During landing, if you do not observe an indication of friction-limited wheel braking (where an increase of force on the brake pedals does fails to produce an increase of deceleration), the appropriate response to a braking action query is “braking action nil.”
(See paragraph 4.8.1.4 above.)
4.8.2 E xample. With proper training, the criteria listed above can be readily observed by pilots.
Consider an airplane that weighs 120,000 lbs. During landing, 100,000 lbs. of that weight will be supported by the main landing gear, which is equipped with wheel brakes, and the remaining 20,000 lbs. will be supported by the nose landing gear, which does not have wheel brakes. In this condition, an accurate mapping of the observed forces could be described in terms of braking action in the following manner:
1. G ood: A 120,000 lbs. airplane could experience a wheel braking force on the order of 30,000 lbs. or approximately 0.3 Gs.
2. Medium: A 120,000 lbs. airplane would only experience a braking force on the order of 16,000 lbs., approximately a 47 percent decrease from GOOD braking.
3. Poor: A 120,000 lbs. airplane would experience a wheel braking force on the order of 7,000 lbs.; this is approximately a 57 percent decrease from MEDIUM and approximately 77 percent from GOOD.
Figure 4-1. An Expectation of Good, Medium, and Poor Braking GOOD - This level of braking capability is typically seen on a wet runway where aggressive braking can still be achieved and directional control is not significantly compromised.
MEDIUM - This level of braking capability is typically seen on snow covered runways.
Wheel braking forces can still be discriminated, and their effectiveness modulated but at a noticeably reduced level.
POOR - This level of braking capability is typically seen on an ice-covered runway or when hydroplaning in heavy rain.
Braking and directional control is minimal. Increased brake application does not produce any increase in deceleration.
Figure courtesy of Robert Kostecka
4.8.3 Usage. It is recommended that pilots refrain from making reports using the phrasesigood to medium" and "medium to poor" unless they have been specifically trained on how to recognize those conditions. In the absence of that training, we encourage pilots to be conservative and report the lowest braking action level observed.
4.9 Pilot or Pilots Reporting Conventions. Both PBAR and ABAR are normally considered valid for the entire runway. Braking action reports may be reported with reference to the applicable third of the runway, although this is not a requirement. Airport operators may also report runway surface conditions by runway thirds.
4.9.1 Examples. The following examples illustrate:
1. Braking action reports applicable to the full runway length:
• PBAR: "Tower, flight XXX experienced POOR braking."
• ABAR: "Ground, flight XXX would like to report an ABAR of MEDIUM."
4-6
4-7
2. Braking action reports applicable to a specific portion of the runway:
• PBAR: “Tower, flight XXX experienced POOR braking due to standing water at the intersection of runways 33 and 10.”
• ABAR: “Ground, flight XXX would like to report an ABAR of MEDIUM on the last third of the runway just before the turnoff at Juliet.”
4.10 Comparison of Braking Action Reports: PBAR vs ABAR.
4.10.1 Accuracy and Precision. Braking action reports are of the greatest value when accuracy and precision are maximized.
4.10.1.1 A c lear understanding of accuracy and precision is important when comparing the relative advantages and limitations of braking action reports which are based on pilot observations (PBARs) and reports automatically generated by systems using aircraft data (ABARs).
4.10.1.2 With respect to braking action reports, accuracy refers to the degree to which the braking action report correctly correlates to the braking levels in the RCAM. Precision refers to the ability of a braking action report to consistently represent a given value for a given observation.
4.10.1.3 The concepts of precision and accuracy are illustrated in Figure 4-2. Accuracy is represented by how close we are to the bullseye; precision is represented by the closeness of the grouping.
Figure 4-2. Precision and Accuracy
4-8
4.10.2 Limitations and Advantages of Braking Action Reporting Methods. Figure 4-3 illustrates how precision and accuracy are affected when braking action reports are made under the described conditions.
Figure 4-3. Comparison of Various Braking Action Reports B raking Action Report
• W ith little or no guidance and training, current braking action reports can be subject to large variations in accuracy and precision.
Pilot Braking Action Report (PBAR)
• With effective training on the elements of braking action and their reporting, the precision of standardized observations and the accuracy of their mapping can be significantly increased.
• Harmonizes engineering analysis methods with the braking levels that can be discerned by the pilot.
Aircraft Braking Action Report (ABAR)
• ABAR systems provide the highest level of accuracy and precision.
• ABAR systems most effectively serve as the basis for continuous improvement in the safety assurance process.
4.10.3 Validate. By providing timely information relevant to all aircraft with similar braking systems, PBARs can be used by pilots to make assessments that affirm or counter the RCAM’s predicted level of performance and by airport operators to confirm or downgrade a RwyCC. To achieve these purposes, it is important that the guidance in this AC regarding PBARs (i.e., braking action reports that are accurate and precise) be followed.
4.11 Recommended Action. O perators should use the information provided in this AC to review and assess the risks associated with operations on wet and contaminated runways and update or modify their procedures, as appropriate, to mitigate these risks. The information should also be included in operations manuals, SOPs, training programs, and any other established means of conveying safety and operational information within the organization.