U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Mitigating the Risks of a Runway Overrun Upon Landing Date: 9/17/14 Initiated by: AFS-800 AC No: 91-79A Change:
1. PURPOSE. This advisory circular (AC) provides ways for pilots and airplane operators to identify, understand, and mitigate risks associated with runway overruns during the landing phase of flight. It also provides operators with detailed information that operators may use to develop company standard operating procedures (SOP) to mitigate those risks.
2. AUDIENCE. This document provides guidance to pilots and flightcrews, airplane operators, certificate holders, program managers, training providers, pilot examiners, and other support personnel. Pilots, airplane operators, certificate holders, program managers, training centers, and other support personnel should adopt the recommended procedures found in this AC to enhance awareness of the risks inherent during the landing phase of flight and the mitigations to employ to reduce the risk of a runway landing overrun.
3. APPLICABILITY. The focus of the content of this AC is primarily on operations not covered by Safety Alerts for Operators (SAFO) 06012, Landing Performance Assessments at Time of Arrival (Turbojets). Any values or examples provided in this AC are estimated values.
Consult manufacturer information for specific guidance applicable to a given airplane model.
However, in the absence of specific landing performance data provided by the airplane’s manufacturer, the pilot/operator is encouraged to use the most conservative landing performance information presented in this AC. Further, the operator may consider these concepts as additional information in conjunction with an operator’s specific operations specifications (OpSpecs) or management specifications (MSpecs) and the airplane’s pilot’s operating handbook (POH), or Airplane Flight Manual (AFM), as appropriate.
4. RELATED READING MATERIAL (current editions):
• AC 23-8, Flight Test Guide for Certification of Part 23 Airplanes;
• AC 25-7, Flight Test Guide for Certification of Transport Category Airplanes;
• AC 60-22, Aeronautical Decision Making;
• AC 120-71, Standard Operating Procedures for Flight Deck Crewmembers;
• AC 121.195(d)-1, Operational Landing Distances for Wet Runways; Transport Category Airplanes;
• Approach and Landing Accident Reduction (ALAR)/Runway Excursion Risk Reduction (RERR) Tool Kits;
• FAA-H-8083-25, Pilot’s Handbook of Aeronautical Knowledge;
• FAA-H-8083-3, Airplane Flying Handbook;
• Flight Safety Foundation (FSF) ALAR Tool Kit; FSF ALAR Briefing Notes, 8.3, Landing Distances; 8.4, Braking Devices; 8.5, Wet or Contaminated Runways; 6.4, Bounce Recover-Rejected Landing; and 2.1, Human Factors.
• Reducing the Risk of Runway Excursions, FSF;
• Safety Targeted Awareness Report (STAR), Overruns on Landing, from the European Regions Airline Association (ERA) Air Safety Work Group;
• SAFO 06012, Landing Performance Assessments at Time of Arrival (Turbojets); and
• SAFO 10005, Go-Around Callout and Immediate Response.
5. BACKGROUND. According to Federal Aviation Administration (FAA) and National Transportation Safety Board (NTSB) information, runway overruns during the landing phase of flight account for approximately 10 incidents or accidents every year with varying degrees of severity, with many accidents resulting in fatalities. The NTSB also concludes that because of the dynamics of a tailwind approach and landing, particularly on wet or contaminated runways, the FAA should provide current and comprehensive guidance regarding the risks associated with tailwind landings and raise awareness of the reduced margins of safety during tailwind landing operations. Therefore, the NTSB recommended that the FAA revise AC 91-79, Runway Overrun Prevention, to include a discussion of the risks associated with tailwind landings and landings on wet or contaminated runways.
a. Strategy. Focused training and testing of pilots and flightcrews, combined with training-based scenarios, are the tools to preventing runway overrun events. Targeted emphasis on training and checking during initial pilot certification, recurrent training, and checking events must not merely be an academic event, but must be practical in order to increase a pilot’s recognition of a higher-risk landing operation.
b. Necessity of Training. Focused training and testing of pilots and flightcrews, combined with training-based scenarios, are important tools for preventing runway overrun events.
c. Operator and Pilot Responsibility. Operators are responsible for developing training programs, SOPs, and complying with all of the regulatory requirements for the flight. All pilots are responsible for knowing the operational conditions they will be encountering and being able to assess the impact of environmental situations on the airplane’s landing distance. This responsibility includes following company SOPs and/or industry best practices and exercising the highest level of aeronautical decision-making (ADM) to ensure the safety of the flight.
NOTE: This guidance pertains to the preflight planning requirements of Title 14 of the Code of Federal Regulations (14 CFR) part 91, §§ 91.103,
91.1037, and 91.605; part 121, § 121.195; and part 135, § 135.385.
6. DISCUSSION—HAZARDS ASSOCIATED WITH RUNWAY OVERRUNS. In order to develop risk mitigation strategies and tools, it is important to identify hazards associated with runway overruns. A study of FAA and NTSB data indicates that the following hazards increase the risk of a runway overrun:
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• Unstabilized approach;
• High airport elevation or high-density altitude, resulting in increased groundspeed;
• Effect of excess airspeed over the runway threshold;
• Airplane landing weight;
• Landing beyond the touchdown point;
• Downhill runway slope;
• Excessive height over the runway threshold;
• Delayed use of deceleration devices;
• Landing with a tailwind; and
• A wet or contaminated runway.
a. What is an Unstabilized Approach? Safe landings begin long before touchdown.
Adhering to the SOPs and best practices for stabilized approaches will always be the first line of defense in preventing a runway overrun. See Appendix 4, Unstabilized Approach Case Study, for an example of an unstabilized approach that led to a runway overrun.
b. High Airport Elevation. High airport elevation or high density altitude results in a higher true airspeed (TAS), ground speed, and a corresponding longer landing distance, compared to low airport elevation or low density altitude.
NOTE: For example, at 1,000-ft airport elevation, with a landing distance factor (see Appendix 1, Suggested Procedures and Training Information) of
1.05 to 1.10 (depending on runway condition), the crew should apply to the landing distance achieved at a sea-level airport elevation. The AFM/POH usually includes the adjustment for this factor.
c. The Effect of Excess Airspeed. The pilot must be aware of airspeed during the approach and of the targeted reference landing airspeed (VREF)/airspeed, plus wind gust adjustments, over the runway threshold. An excessive approach speed may result in an excessive speed over the runway’s threshold, which may result in landing beyond the intended touchdown point as well as a higher speed from which the pilot must bring the airplane to a stop. (Refer to the current editions of FSF ALAR Briefing Note 8.3—Landing Distances, and Boeing’s Takeoff/Landing on Wet and Contaminated Runways.)
(1) FSF ALAR Briefing Note 8.3. A 10 percent increase in final approach speed results in a 20 percent increase in landing distance. This assumes a normal flare and touchdown (i.e., not allowing the airplane to float to bleed excess airspeed).
(2) Example. Runway length available is 5,000 ft and the airplane’s AFM/POH certified landing distance may be up to 3,000 ft at the correct airspeed at the threshold crossing point.
However, given a 10 percent increase in airspeed over the runway threshold, increasing the landing distance 20 percent, the resultant operational landing distance is now 3,600 ft
(1.20×3,000).
d. Airplane Landing Weight. Any item that affects the landing speed or deceleration rate during the landing roll will affect the landing distance. The effect of gross weight on landing distance is one of the principal items determining the landing distance of an airplane. One effect Par 6 Page 3
of an increased gross weight is that the airplane will require a higher landing speed. When one considers minimum landing distances on a dry runway, braking friction is the main source of deceleration. The minimum landing distance will vary in direct proportion to the gross weight.
NOTE: For example, a 10 percent increase in gross weight at landing would result in a 5 percent increase in landing velocity and a 10 percent increase in landing distance. (Refer to the Pilot’s Handbook of Aeronautical Knowledge for more information.)
e. Landing Beyond the Intended Touchdown Point. AFM/POH distances are based on a touchdown point determined through flight-testing procedures outlined in the current editions of AC 25-7 and AC 23-8. If the airplane does not touch down within the air distance included in the AFM or POH landing distance, it will not be possible to achieve the calculated landing distance.
f. Downhill Runway Slope. A negative runway slope of 1 percent (downhill) increases landing distance by 10 percent (a factor of 1.1). (Refer to FSF ALAR Briefing Note 8.3 and Appendix 1, Table 1-3, Sample Computation: Runway Length7,000 ft.)
g. Excessive Height Over the Runway Threshold – Threshold Crossing Height (TCH) Greater Than 50 ft (Excess TCH). The certified landing distances furnished in the AFM are based on the landing gear being at a height of 50 ft over the runway threshold. For every 10 ft above the standard 50 ft threshold height, landing air distance will increase 200 ft.
NOTE: For example, TCH of 100 ft increases the landing distance by about 1,000 ft (50 additional ft divided by 10 = 5 X 200 ft landing distance increase per each 10 ft above 50 ft TCH = 1,000 ft additional landing distance). (Refer to FSF ALAR Briefing Note 8.3.)
h. Delayed Use of Deceleration/Maximum Braking.
(1) For those airplanes so equipped, deceleration devices consist of spoilers, thrust reversers, and brakes. The touchdown point is important since the wheel brakes are much more effective in retarding the airplane than the air drag during the airborne part of the landing distance. The sooner the airplane touches down and starts braking, the shorter the total distance will be. The FSF ALAR Task Force found that delayed braking action during the landing rollout was involved in some of the accidents and serious incidents in which slow/delayed crew action was a causal factor. The FSF Runway Safety Initiative (RSI) team found that improper use and malfunction of speed brakes, wheel brakes, and reverse thrust were significant factors in a number of runway excursion landing accidents.
(2) Prompt and proper operation of all means of deceleration has a major influence on landing distances. Spoilers greatly decrease lift, dump the weight on the wheels, and thereby make the brakes effective. It should be noted that manual spoilers, operated by the pilot, involve a delay. Even 2 seconds at speeds of 200 ft/second (118 knots (kts)) can increase the stopping distance by almost 400 ft. Landing distance data in the AFM is typically based on a time increment of 1 second between successive actions to manually deploy/engage the deceleration devices (see Figure 1, Assumed Landing Time Delays in Deriving the Scheduled Landing Distance). A conservative approach is to add 200 ft to the landing distance for every second in Page 4 Par 6
excess of 2 seconds to deploy the airplane’s deceleration devices. A prudent pilot will make a reasonable adjustment to the airplane’s landing distance for any delay in employing the airplane’s deceleration devices. Figure 2, Braking Devices on Stopping Energy and Stopping Distance, shows the relative effectiveness of each of the deceleration devices during the landing roll (refer to FSF ALAR Briefing Note 8.4).
FIGURE 1. ASSUMED LANDING TIME DELAYS IN DERIVING THE SCHEDULED
LANDING DISTANCE
• Segment 1. This segment represents the flight test measured average time from touchdown to pilot activation of the first deceleration device. For AFM data expansion, use the longer of 1 second or the test time.
• Segment 2. This segment represents the flight test measured average test time from pilot activation of the first deceleration device to pilot activation of the second deceleration device. For AFM data expansion, use the longer of 1 second or the test time.
• Segment 2 is repeated until pilot activation of all deceleration devices has been completed and the airplane is in the full braking configuration.
NOTE: For approved automatic deceleration devices (e.g., autobrakes or auto-spoilers, etc.) for which performance credit is sought for AFM data expansion, established times determined during certification testing may be used without the application of the 1-second minimum time delay described in the appropriate segment above.
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FIGURE 2. BRAKING DEVICES ON STOPPING ENERGY AND
STOPPING DISTANCE
FIGURE 3. THRUST REVERSE EFFECTIVENESS
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FIGURE 4. SECONDS COUNT – REVERSE THRUST APPLICATION SEQUENCE (BOEING PERFORMANCE TAKEOFF/LANDING ON WET, CONTAMINATED, AND
SLIPPERY RUNWAYS)
(3) Be conservative and add 20 percent to the rollout distance if the pilot does not maintain maximum braking until the airplane reaches a full stop. Otherwise, if available, use AFM data for less than maximum braking.
(4) For airplanes that do not have antiskid brakes, spoilers, or thrust reverse, caution should be exercised. Excessive braking can lead to causing a tire failure or cause a skidding condition, leading to a runway excursion. Therefore, flying a stabilized approach and timely application of deceleration devices are the keys to a safe landing.
NOTE: Example: Available runway 5, 000 feet (ft), AFM landing distance 3,000 ft, at correct speed, and at 50-ft TCH, a total of 3 seconds to deploy the airplane’s deceleration devices, results in 1 second over the AFM landing distance assumed 2 seconds to deploy deceleration device will result in an additional 200 ft operational landing distance, for a total of 3,200 ft.
i. Landing with a Tailwind – Effect of a Tailwind on Landing Distance. The effect of a tailwind on landing distance is significant and is a factor in determining the landing distance required. Given the airplane will land at a particular airspeed, independent of the wind, the principal effect of a tailwind on operational landing distance is the change in the ground speed at which the airplane touches down.
(1) The effect of a tailwind will increase the landing distance by 21 percent for the first 10 kts of tailwind. (Refer to the Pilot’s Handbook of Aeronautical Knowledge, and the aircraft’s AFM/POH data to determine if tailwind landing data is available for the airplane.)
(2) Tailwind 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, Par 6 Page 7
tailwind landing data may not be provided. The FAA Small Airplane Directorate provided the following tailwind performance information for a few small airplanes:
• Cessna 150, 152, note on the landing distance chart, “for operation with tailwinds up to 10 knots, increase distances by 10 percent for each 2 knots.”
• TMB 850, note under landing distance table to “increase total distances of 30 percent for every 10 knots of tailwind.”
• The Cirrus and Columbia are two very popular piston airplanes. The Cirrus uses the same note in the chart as Cessna. The Columbia is like the Diamond airplane and offers factors for grass but not tailwinds.
NOTE: Remember to account for the effect of a tailwind on landing distance, whether you are flying a large or small airplane.
(3) Tailwind example: Available runway 5,000 ft, AFM landing distance 3,000 ft, TCH at 50 ft 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 a total of 3,630 ft.
j. A Wet or Contaminated Runway. Landing distances in the manufacturer-supplied AFM provide performance in a flight test environment that is not necessarily representative of normal flight operations. For those operators conducting operations in accordance with specific FAA performance regulations, the operating regulations require the AFM landing distances to be factored to ensure compliance with the pre-departure landing distance regulations. These factors should account for pilot technique, wind and runway conditions, and other items stated above.
Pilots and operators should also account for runway conditions at the time of arrival (TOA) to ensure the safety of the landing. Though the intended audience of SAFO 06012 is turbojet airplanes, it is highly recommended that pilots of non-turbojet airplanes also follow the recommendations in SAFO 06012.
(1) The SAFO urgently recommends that operators develop a procedure for flightcrews to assess landing performance based on conditions actually existing at the TOA, as distinct from conditions presumed at time of dispatch. Those conditions include weather, runway conditions, the airplane’s landing weight, landing configuration, approach speed, and the flightcrew deploys deceleration devices in a timely manner.
(2) Once the actual landing distance is determined, an additional safety margin of at least 15 percent should be added to that distance. Except under emergency conditions, flightcrews should not attempt to land on runways that do not meet the assessment criteria and safety margins as specified in SAFO 06012.
(3) A safety margin of 15 percent should be added, and the resulting distance should be within the runway length available. The FAA considers a 15 percent margin to be the minimum acceptable safety margin.
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NOTE: The flightcrew should not apply this 15 percent safety margin to the landing distance determined for compliance with any other OpSpec/MSpec requirement.
(4) Know you can stop within the landing distance available. The cumulative effect of the conditions that extend the airplane’s landing distance, plus the 15 percent safety margin, can be a substantial increase to the AFM/POH data, unless the pilot is aware of the items presented, and possesses the knowledge and flying discipline to mitigate the risk of a runway overrun.
See below Table 1, The Effects of Compound Factors—The End is Closer Than You Think.
TABLE 1. THE EFFECTS OF COMPOUND FACTORS—THE END IS CLOSER THAN
YOU THINK
7. RISK MITIGATION.
a. SOP. 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. As a minimum, the SOPs should contain the factors presented in this AC.
b. Runway Overrun Mitigation Training Curriculum. An effective training program is the next tool that provides academic 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 Par 6 Page 9
include the same elements contained in their SOP. Also, the go-around maneuver and the reasons to initiate a go-around maneuver must be part of their training. (Refer to SAFO 10005.)
NOTE: Operators should also incorporate this training into their pilot and dispatcher training for operations conducted in accordance with 14 CFR parts 121, 135, 125, 91, 91K, 141, and 142. Further, all independent certificated flight instructors (CFI) should also provide this training to the pilots they train.
c. Flight Checking and Recurrent Training. Checking, testing, and recurrent training that emphasizes airplane landing performance are essential tools to mitigate runway overruns.
Designated Pilot Examiners (DPE), flight and ground instructors, check airman, and dispatch examiners should specifically stress ADM, runway overrun risk management scenarios, and the elements within this AC as they qualify, train pilots, flightcrews, and dispatchers to exercise the privileges of their certificate. Trainers and examiners must include runway overrun mitigation strategies during training and checking to ensure the pilot/applicant can apply the principles in a real-world environment.
NOTE: The following appendices provide additional information for operators and pilots to develop SOPs, training programs, pilot techniques, and case study.
John Barbagallo Acting Deputy Director, Flight Standards Service Page 10 Par 7
Appendix 1 APPENDIX 1. SUGGESTED PROCEDURES AND TRAINING INFORMATION
1. ORGANIZATION. This appendix divides the discussion of runway overruns during the landing phase of flight into the following broad categories:
• Definitions;
• The necessity to fly a stabilized approach to the touchdown aiming point;
• A discussion of landing performance data; and
• Landing and braking techniques.
2. DEFINITIONS. The following, though not all inclusive, are definitions of landing elements that form the foundation for a successful landing.
a. Declared Runway Distance. Declared distances for a runway represent the maximum distances available and suitable for meeting takeoff and landing distance performance requirements. All Title 14 of the Code of Federal Regulations (14 CFR) part 139 airports report declared distances for each runway. For runways without published declared distances, the declared distances may be assumed to be equal to the physical length of the runway unless there is a displaced landing threshold. (Refer to the Aeronautical Information Manual (AIM) for more information.)
b. Landing Distance Available (LDA). The length of the runway declared available for landing. This distance may be shorter than the full length of the runway due to a threshold displacement.
c. Actual Landing Distance. The landing distance for the reported meteorological and runway surface conditions, runway slope, airplane weight, airplane configuration, approach speed, use of autoland or a Head-Up-Guidance System (HGS), and ground deceleration devices planned to be used for the landing. It does not include any safety margin and represents the best performance the airplane is capable of for the conditions. (Refer to SAFO 06012, Landing Performance Assessments at Time of Arrival (Turbojets), for more information.)
d. Braking Action Reports. When available, air traffic control (ATC) furnishes pilots the quality of braking action received from pilots or airport management. The quality of braking action is described by the terms “good,” “fair (medium)” (see note below), “poor,” and “nil,” or a combination of these. When pilots report the quality of braking action by using the terms noted above, pilots should use descriptive terms that are easily understood, such as “braking action is poor the first/last half of the runway,” and include the type of airplane. When tower controllers have received runway braking action reports, which include the terms fair (medium) (see note below), poor, or nil, or whenever weather conditions are conducive to deteriorating or rapidly changing runway braking conditions, the tower will include on the automated terminal information service (ATIS) broadcast the statement, “Braking Action Advisories are in Effect.”
(Refer to the AIM for more information.) See Table 1-1, Operational Runway Condition Assessment Matrix (RCAM) Braking Action Codes and Definitions, below. (See the notes below for the RCAM for clarification and information of terms and addition of codes.)
Appendix 1 NOTE: The braking action term “FAIR” is in the process of being changed to “MEDIUM” throughout the Federal Aviation Administration (FAA).
Until an official language change is published, the current guidance of the term “FAIR” is used.