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1. To find the landing distance required, multiply the unfactored AFM landing distance by the applicable LDF in Table 3-1 for the runway conditions existing at the TOA.
2. If the AFM landing distances are presented as factored landing distances, first adjust the data to remove the preflight factors that were applied prior to multiplying the distance by the LDF. (See appropriate examples in Chapter 2.)
3. The LDFs given in Table 3-1 include a 15 percent safety margin.
Table 3-1. Landing Distance Factors The following factors are multipliers to the unfactored AFM demonstrated landing distances:
Runway Condition Code 6 5 Grooved/ PFC 5 Smooth 4 3 2 1 Braking Action Dry Good Good Good to Medium Medium Medium to Poor Poor Turbojet, No Reverse 1.67 2.3 2.6 2.8 3.2 4.0 5.1 Turbojet, With Reverse 1.67 1.92 2.2 2.3 2.5 2.9 3.4 Turboprop (see Note) 1.67 1.92 2.0 2.2 2.4 2.7 2.9 Reciprocating 1.67 2.3 2.6 2.8 3.2 4.0 5.1 Note: These LDFs apply only to turboprops when the AFM provides for a landing distance credit for the use of ground idle power lever position. Turboprops without this credit should use the “Turbojet, No Reverse” LDFs.
3.4 Runway Condition Considerations. Airport assessments should be based on information that most accurately represents the conditions anticipated. When available for the portion of the runway that will be used for landing, the following are considered:
• RwyCCs,
• Expected runway condition (contaminant type and depth), and
• Braking action reports.
3.4.1 Timeliness. It is important to note the time of the latest RwyCC and any associated reliable braking action reports. Several overruns have occurred when pilots were provided with a runway condition that was no longer reliable given changes in meteorological conditions.
3-4 ATTENTION: Pilots are strongly advised to review the weather conditions and compare that to the time of the latest braking action report.
3.4.2 S ituational Awareness. Throughout the descent and approach, pilots should remain vigilant for any deterioration in conditions. You should use all available resources to determine what condition you may expect upon landing to include ATC reports, field condition reports, flight visibility, and onboard weather radar.
3.5 R isks Associated With Moderate or Hea vy Rain. Several runway excursions and overruns have raised concerns with wet runway stopping performance assumptions.
Analysis of the stopping data from these incidents and accidents indicates the braking coefficient in each case was significantly lower than expected for a wet runway than would be predicted by § 25.109 and AC 25-7. These incidents and accidents occurred on both grooved and ungrooved runways. The data indicates that applying a 15 percent safety margin to wet runway advisory data, as recommended (see Figure 5-1, Effects of Compound Factors), may be inadequate in certain wet runway conditions.
3.5.1 Rainfa ll Amount. In a rainfall event, such as an active thunderstorm, the amount of water or moisture on a runway can change rapidly. The dynamic nature of rainfall can present challenges for the timely and accurate reporting of water or moisture on a runway.
3.5.2 Risk Mitigation. It is recommended that if it is anticipated that more than 1/8 inch of water will be on the runway, the LDF associated with medium to poor braking, or a Rwy CC of 2, be used during the TOA assessment. In addition, when planning to land on a smooth runway under conditions of moderate or heavy rain, or when landing on a grooved or PFC runway under heavy rain, pilots should consider that the surface may be contaminated with water at depth greater than 1/8 inch and adjust their landing distance assessment accordingly.
Note: A Special Weather Observation (SPECI) will only be generated if a thunderstorm begins. A SPECI is not generated when rainfall rates simply change.
In addition, ATC radar is not optimized for the detection of rainfall and during an active or fast-moving weather event, PIREPs can rapidly become obsolete.
3.6 Risk Associated With Standing Water. When standing water is present, aircraft braking can rapidly degrade as the contact area of the tire is lifted away from the pavement by the effects of hydroplaning. When this occurs, pilots have reported that the aircraft feels like it accelerates. This change in sensation is because braking performance can degrade in a matter of seconds, resulting in up to a 77-percent decrease in braking force. This rapid decrease in friction also affects cornering ability, making lateral drift more difficult to control, if not impossible. Unexpected handling characteristics due to standing water have been shown to lead to pilot confusion and a possible delay in the use of thrust reversers or ground spoilers.
3.6.1 RwyCC Limitations. Note on the RCAM (see Table 3-2, Pilot/Operator Runway Condition Assessment Matrix (RCAM)) that only 1/8 inch of water separates a wet r unway (with a RwyCC of 5 and “good” braking action) from a runway contaminated
3-5 with standing water (and a RwyCC of 2 and “medium to poor” braking action). This dramatic difference is due to the possibility of dynamic hydroplaning that may occur any time water depth exceeds 1/8 inch.
3.6.2 O perations at Foreign (Non-U.S.) Airports.
3.6.2.1 Pilots should be aware that the design and maintenance standards referenced in this AC might not be met in other countries. Standards for design, construction, and maintenance of runways are based on ICAO Annex 14, Aerodromes, standards; however, they may lack oversight in implementation of those standards.
3.6.2.2 O utside of the United States, there is often less usage of grooving or PFC overlay which, when present, will normally aid in drainage, mitigate the risk of hydroplaning during active precipitation, and improve braking action.
Unless the pilot is knowledgeable of an international airport’s runway maintenance program, and sure that the runway has improved drainage capabilities with grooved or PFC surfaces, they should consider basing their TOA assessment on the recommendations in paragraph 3.6.1.
3.7 Aircraft Performance Considerations. In addition to runway surface conditions, the following considerations may also impact operational landing distance calculations:
• Runway slope,
• Airport pressure altitude,
• Wind,
• Temperature,
• Airplane weight and configuration,
• Approach speed at threshold,
• Adjustment to landing distance (such as autoland), and
• Planned use of airplane ground deceleration devices.
Note: Risk of overrun linked to a runway being more slippery than expected is amplified in tailwind conditions (increased ground speed at touchdown and potential floating aircraft). This potential situation needs particular attention.
3.8 Autobrake and Manual Brake Usage. When autobrakes are a part of the aircraft’s landing configuration, the landing distance assessment is not intended to force a higher than necessary autobrake selection. Autobrakes normally target a deceleration rate and may not require the employment of the full braking capabilities of the aircraft.
Conversely, landing calculations using manual brakes assume that the full capability of the aircraft’s wheel brake system is employed during the rollout phase.
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3.8.1 Safety Margin. To accommodate for real-world operational variations, the manual wheel braking landing distance used for a TOA assessment should include a safety margin of at least 15 percent. For operations when the runway is dry, or when the runway is wet, grooved, or PFC, if the manual braking distance provides a 15 percent safety margin, then the braking technique may include a combination of autobrakes and manual brakes even if the selected autobrake landing data does not provide a 15 percent safety margin.
The operator will need to ensure that proper procedures and crew training are in place when the selected autobrake landing data does not provide a 15 percent safety margin.
3.8.2 C ontaminated Runways. For contaminated runways, the minimum 15 percent safety margin should always be based on either autobraking or manual braking to be used
(i.e., should correspond to the selected level of autobrake, if used).
3.9 Touchdown Point. The touchdown point used in the landing distance assessment reflects the assumed air distance. Operational landing data usually includes an allowance for 1,500 ft or 7 seconds of air distance from the threshold to touchdown. An air distance as short as 1,000 ft may be used provided an operator’s landing assessment procedures include enhancements to minimize the risk of overruns or undershoots, including:
1. Training in touchdown control and short field landing techniques.
2. Identification of required touchdown point and training to assure go-around procedures are initiated if unable to achieve a suitable touchdown point.
3. Approach guidance and runway markings on the specific runway are consistent with a shorter air distance.
4. Operational data provided to the crew for the specific runway, conditions, and aircraft-landing configuration without the need for interpolation.
5. The flight techniques assumed in the creation of the performance data used for shorter air distances are appropriately trained and documented. For example, the assumed speed bleed-off used in the performance data needs to be consistent with the trained flight techniques for flaring the aircraft.
3.10 Crosswind Considerations. During operations when standing water may be present, operators should be aware of the effect of crosswind landing on a contaminated runway, given most aircraft only provide demonstrated crosswind and not a maximum crosswind limit. Tire cornering limitations can reduce wheel braking capability. As a result, crosswind limits can become a dominant factor in TOA landing distance assessments.
Pilots should always be vigilant of these limits, especially when braking action is less than good.
3.11 Assessment Based on Preflight (Dispatch) Criteria. When the runway is dry, the assessment may be as simple as confirming that the runway meets the criteria used for dispatch. To use an assessment based on preflight (dispatch) criteria, pilots need to:
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1. Ensure that the runway used for landing is the same runway that was assessed during preflight or for dispatch;
2. Confirm that the wind velocity and other factors that could affect landing distance are the same as those considered during preflight or the dispatch assessment; and
3. When applicable, consider the possibility of a late runway change such as a side step to a parallel runway.
3.12 Risk Management Considerations. Landing on a contaminated runway can involve multiple hazards, including cognitive bias, changing weather conditions, and high task loading. Because these hazards occur at a time with pressing time constraints, they can create an environment where errors are likely to occur. Managing such risks requires mitigation in the form of organizational policies, effective training, and well-designed procedures.
3.12.1 Policy Considerations. The overall strategy for managing risk should involve structured briefings during times of low task loading to address contingencies should new information be received. Once in the terminal area, the pilots should focus on the execution of the briefed plan, not analysis of the risk. While flightcrews always need a decision space for unexpected events, primary decision points concerning acceptable risk should be clearly communicated by the operator.
3.12.2 F lightcrew Training Considerations . Ensure that briefings are complete, checklists are run correctly, and that plan continuation bias does not drive actions counter to established rules and SOPs. This should be the primary goals of the pilot monitoring.
3.12.3 P rocedure Considerations . Decisions regarding TOA landing distance assessments should be made using the best available information considering timeliness, reliability, and data precision. SOPs should require that when runway conditions are likely to change, crews brief the worst braking levels acceptable and the indications that would accompany them.
This briefing needs to take place prior to descent. Once the descent begins, pilots actively monitor conditions and when faced with a pre-briefed scenario, respond with the previously briefed set of actions.
3.13 Technical Considerations for Understanding Landing Performance and the RCAM.
Much like how aircrews must have a technical knowledge of their aircraft’s systems and not just checklists and procedures, a basic engineering background on wheel braking and runway friction can serve to greatly enhance the guidance in this AC. As an aid for good decision making, a knowledge of runway friction and training on the RCAM is provided.
3.13.1 Runway Friction. The ability of a runway to act as an agent for an aircraft to transfer its weight into wheel braking force during landing is a function of the runway surface friction characteristics and the wheel braking system of the aircraft.
3.13.1.1 Runway Friction Properties Runway pavement is a function of the large-scale and small-scale properties of the pavement, known as macro and micro texture. Airports construct and aircraft are certified for runways whose
3-8 pavement properties can be shown to support a minimum amount of friction when measured with a testing device. These tests are typically done in dry conditions with devices that have self-wetting capabilities.
3.13.1.2 Wet Runways. When there is a possibility that the runway surface is lubricated with water to a degree large enough to affect wheel braking performance, the runway is reported as “wet” and classified in the RCAM with the number 5. Airports are required to accomplish routine friction testing.
Should such a test result in a value below a specified threshold, the runway is listed with a Notice to Air Missions (NOTAM) of “Slippery when Wet.”
Runway friction is also affected by any substance that is found on top of the pavement. When this occurs, the runway is said to be “contaminated.”
3.13.1.3 Water Removal. Runways are normally constructed with a built-in crown so that water will drain towards each side. To aid in this drainage, pavement can be designed with lateral grooves or with a special pavement property known as PFC overlay. Grooved runways increase the rate of water drainage through the polished channels in the grooves while PFC surfaces allow water to drain through the surface. The primary purpose of each is to facilitate the dynamic drainage of water below the aircraft tire as it rolls over the surface. However, these runway improvements do not affect the basic lubricating properties water has on the texture of the pavement itself.
3.13.2 T ypes of Contamination. Any substance that rests on the surface of a pavement can have three distinct properties. These are:
3.13.2.1 So lid Contaminant. The substance represents a non-movable surface that has its own friction properties. These properties can exhibit a wide range of friction, with relatively high friction available when hot sand is bonded to very cold ice to very poor friction. While solid contaminant is mostly encountered as frozen water, it can occur as a result of rubber buildup or in rare occasions, growths such as lichen.
3.13.2.2 Loose Contaminant. A condition whereby a substance compresses directly under a rolling tire but has a depth to a degree that the tire must also displace it as well.
3.13.2.3 Deformable Contaminant. A condition whereby a substance resting above the surface of the pavement acts to deform away from underneath the tire as it rolls. Deformable contaminant can be extremely hazardous as it can lift the tire away from the surface and result in hydroplaning.
3.13.3 T akeoff Performance . During takeoff, aircraft performance may be limited with consideration of loose contaminant imparting additional drag due to the combination of displacement by the aircraft’s tires and impingement of the contaminant spray on the aircraft structures. AC 25-31 details the guidance recommended under these conditions when determining takeoff performance data.
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