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.
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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."
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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
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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.
5-1 CHAPTER 5. RUNWAY OVERRUN HAZARDS
5.1 Background. In addition to being able to predict and assess aircraft performance on a runway, pilots need to understand and account for other hazards that can significantly affect the landing distance required.
5.2 Overrun Hazards. The following hazards have been shown to increase the risk of a runway overrun.
5.2.1 Unstabilized Approach. Deviations in airspeed, altitude, descent rate, glideslope, runway aim point, and localizer control place pilots in a position where recovery to the desired flight path is unlikely. It is the pilot’s responsibility to inform ATC when compliance with an instruction will result in an unstabilized approach due to speed or descent rate.
5.2.2 E xcess Airspeed . It is critical that the pilot be aware of airspeed during the approach. The recommended approach reference landing airspeed (Vref), plus wind and gust additives, should be maintained until 50 ft over the runway threshold. Excessive approach speed may result in extra speed over the runway threshold and landing beyond the intended touchdown point. In addition to using more runway to touchdown, once the aircraft is on the runway, excessive speed will require more runway to stop, which could lead to a runway overrun. As a rule of thumb, on dry or wet runways, a 10 percent increase in final approach speed results in a 20 percent increase in landing distance. For example, published Vref is 120 knots (kt) with a landing distance of 3,000 ft. If the aircraft crosses the runway threshold at 132 kts, the aircraft will require 3,600 ft to stop.
5.2.3 E xcessive Height Over the Runway Threshold. The landing distances provided in the AFM are based on the aircraft being at 50 ft over the runway threshold. For every 10 ft above the standard 50 ft TCH, landing distance will increase 200 ft. For example, if the aircraft crosses the threshold at 100 ft, the required landing distance will increase by 1,000 ft. (Refer to FSF ALAR Briefing Note 8.3, Landing Distances.)
5.2.4 Landing Beyond the Intended Touchdown Point. AFM/POH distances are based on a touchdown point determined through flight testing procedures outlined in AC 23-8, AC 25-7, and AC 25-32. If the airplane does not touch down within the air distance included in the AFM/POH landing distance, it may not be possible to achieve the calculated landing distance.
5.2.5 H igh Airport Elevation . High airport elevation or high-density altitude results in a higher true airspeed, groundspeed, and a corresponding longer landing distance, compared to a lower airport elevation. Pilots should be aware that the performance penalty for high airport elevation can be significant. The AFM/POH usually includes an adjustment for this factor. (Refer to § 25.125(a).)
5.2.6 Airplane Landing Weight. Any item that affects the landing speed or deceleration rate during landing affects the landing distance, so the gross weight of the aircraft has a significant effect on landing distance. In other words, the required landing distance varies in direct proportion to the gross weight. For example, a 10 percent increase in landing weight results in a 5 percent increase in landing speed and a 10 percent increase in
5-2 landing distance. (Refer to the Pilot’s Handbook of Aeronautical Knowledge (PHAK) for more information.)
5.2.7 D ownhill Runway Slope . Runway slope has a direct effect on landing distance.
A 1-percent downhill slope increases landing distance by 10 percent (factor of 1.1). This effect is usually only accounted for in performance computations if the downhill runway slope exceeds 2 percent. (Refer to FSF ALAR Briefing Note 8.3.)
5.2.8 Delayed Use of Deceleration Devices/Maximum Braking.
5.2.8.1 For those airplanes so equipped, deceleration devices consist of spoilers/speed brakes, thrust reversers, and brakes. Since wheel brakes are much more effective in slowing the airplane once on the ground than air drag during the airborne part of the landing, pilots should prioritize achieving the intended touchdown point. The sooner the airplane touches down and starts braking, the shorter the total distance will be. Delayed braking action by the flightcrew during the landing rollout has been the causal factor in several accidents and serious incidents. Similarly, improper use of speed brakes, wheel brakes, and reverse thrust have been significant factors in a number of runway excursion landing accidents.
5.2.8.2 Prompt and proper operation of all means of deceleration has a major effect on landing distances. For aircraft with automatic ground spoilers/speed brake deployment but with manual arming, it is of paramount importance that these devices are effectively armed before landing. In addition, once on the ground, deployment should be verified. Spoilers/speed brakes greatly decrease lift, dump the weight on the wheels, and make the brakes effective. It should be noted that manual spoilers/speed brakes operated by the pilot involve a delay.
A 2-second delay at speeds of 200 ft/second (118 kts) increases the airplane stopping distance by almost 400 ft. Landing distance data in the AFM is typically based on a 1-second delay between successive actions to manually deploy/engage the deceleration devices. A conservative approach is to add 200 ft to the landing distance for every second in excess of 2 seconds to deploy the airplane’s deceleration devices.
5.2.9 E ffect of a Tailwind on Landing Distance. The effect of a tailwind on landing distance is significant. Given that the airplane will land at a particular airspeed independent of the wind, the principal effect of a tailwind on landing distance is the change in the groundspeed at which the airplane touches down. The effect of a tailwind increases the landing distance by 21 percent for the first 10 kts of tailwind. (Refer to the PHAK for additional general information and the aircraft’s AFM/POH data to specifically determine if tailwind-landing data is available for your airplane.)
5.2.9.1 T ailwind landings affect all types of airplanes. For transport category airplanes, the effect of tailwind is shown in the AFM landing distance information. For small airplanes, tailwind-landing data may not be provided.
The Aircraft Certification Service (AIR) provided the following tailwind performance information for a few small airplanes:
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1. Cessna 150 and 152: Note on the landing distance chart, “For operation with tailwinds up to 10 knots, increase distances by 10 percent for each 2 knots.”
2. TBM 850: Note under landing distance table to “increase total distances of 30 percent for every 10 knots of tailwind.”
5.2.9.2 Tailwind example: Available runway of 5,000 ft, AFM landing distance of 3,000 ft, 50 ft TCH, and at the correct airspeed with a 10 kts tailwind results in an increase in the operational landing distance of 21 percent. This increase equates to an additional 630 ft, which increases the operational landing distance to 3,630 ft.
5.2.10 Cumulative Effect. The LDA can be exceeded when a cumulative effect of the above conditions exists. Pilots need to be aware of this cumulative effect. An example of the compound effects is in Figure 5-1, Effects of Compound Factors, below.
Figure 5-1. Effects of Compound Factors
1. Base line: At target landing speed, 50 ft at the threshold crossing height, dry runway, zero wind = 0% increase in AFM/POH landing distance.
2. With a 10-ft increase in threshold crossing height = 200-ft increase in landing distance.
3. With a 10% increase in landing speed = 20% increase in landing distance.
4. Plus a 10 kts tailwind, 21% increase in landing distance.
5. Add 20% for less-than-maximum braking and 200 ft for each second greater than 2 seconds to use deceleration devices.
6. Delay to employ deceleration devices. For each second beyond 2 seconds, add 200 ft to the landing distance
7. Add 15% safety margin to the resultant required runway length.
Total landing distance, including safety margin The End 5,000 ft of runway
5.3 Risk Mitigation.
5.3.1 SOPS. Specific SOPs to prevent a runway overrun are a primary risk mitigation tool.
Once SOPs are developed, it is imperative that the pilot/flightcrew execute them faithfully to mitigate a runway overrun. At a minimum, the SOPs should contain the factors presented in this AC.
5.3.2 Runway Overrun Mitigation Training Curriculum. An effective training program provides the knowledge and skill to increase the pilot's awareness of the factors that can cause a runway overrun. At a minimum, the operator's training program should include the same elements contained in their SOPs. Also, the go-around maneuver and the 5-4
5-5 reasons to initiate a go-around should be part of the training program. (Refer to SAFO 10005.)
5.3.3 Certificated Air Operator’s Flight Checking and Recurrent Training. Checking, testing, and recurrent training that emphasize airplane-landing performance are essential tools to mitigate runway overruns. Pilot examiners, flight and ground instructors, check airmen, and dispatch examiners should specifically stress aeronautical decision-making (ADM), runway overrun risk management, and the elements within this AC as they qualify and train pilots and dispatchers. Instructors and examiners should include runway overrun mitigation strategies during training and checking to ensure the pilot/applicant can apply the principles in a real-world environment.
Appendix A A-1 APPENDIX A. AIRCRAFT BRAKING ACTION REPORT (ABAR) SYSTEMS A.1 Overview. The information in this appendix is intended for consideration by flight operations management personnel responsible for creating policies and procedures regarding the use of automated systems that generate ABAR. As such, it provides background information for management purposes and is not intended as an operational guide for pilots.
A.2 Design Philosophy. An ABAR system is a report given describing a level of braking action using data from the aircraft. It will reflect to what degree the weight of an aircraft can be transferred to a deceleration force via the wheel brakes when the anti-skid activates during a friction-limited event. An ABAR system can be located either remotely or onboard an aircraft and uses the aircraft’s data to produce a standardized indication of wheel braking performance.
A.2.1 ABAR systems are the most accurate and objective means of observing and reporting aircraft braking action. The use of aircraft data to generate an ABAR can mitigate the human errors resulting from inadequate training, inexperience, or cognitive bias that may occur with a Pilot Braking Action Report (PBAR).
A.2.2 The data recorded by the ABAR system during the landing roll is used to:
1. Isolate the mechanical wheel braking forces from all other forces contributing to deceleration, as well as identify when wheel braking is friction limited; and
2. Map those forces in friction-limited conditions to the scale used to make braking action reports.
A.2.3 ABAR systems may come from different vendors and apply to different aircraft. A means of assuring that all systems operate within minimum, industry-based engineering standards, is through demonstrated compliance with ASTM E3266, Standard Guide for Friction-Limited Aircraft Braking Measurements and Reporting. Compliance ensures a minimum degree of confidence in all ABAR systems and facilitates a harmonized communication of wheel braking capability between aircraft with similar performance characteristics. (Refer to Advisory Circular (AC) 25-32, Landing Performance Data for Time-of-Arrival Landing Performance Assessments.)
A.2.4 A ircraft systems may also transmit data that is not visible to the flightcrew. Data not visible to the pilot is not considered part of the ABAR, and may be utilized for other data analysis purposes.
A.3 Aircraft Considerations.
A.3.1 ABAR generating systems are considered applicable to a wide range of aircraft types and manufacturers whose design allows for such an analysis.
A.3.2 ABAR systems installed on aircraft may require appropriate supplemental type certification approval.