Appendix 1
d. Wet and Contaminated Runway Surface. When the runway is wet or slippery, reverse thrust (if the airplane is equipped), may be the dominant deceleration force just after touchdown, and throughout the deceleration if the runway has poor or worse braking conditions. As the airplane slows down, the wheel brakes become the dominate deceleration force. When the runway length is limited, for airplanes equipped with an antiskid system, maximum wheel braking should be applied immediately after touchdown. For airplanes without an antiskid system slow back pressure should be applied to the yoke such that it will not raise the nose of a nose gear airplane for aerodynamic braking while maximum braking that will not cause skidding is applied. In all situations, braking should be maintained until the airplane slows to a safe taxi speed for the conditions.
e. Autobrakes. If the airplane is equipped with autobrakes, manufacturers recommend the use of the autobrakes for all landings on contaminated runways. Autobrakes are applied earlier in the landing roll, and to the level selected by the pilot for the anticipated landing condition, runway available, and provide the most efficient and timely use of braking action. However, the pilot must ensure that if the autobrakes do not engage upon touchdown, then manual braking must be applied.
f. Antiskid. Application of brakes is different for airplanes equipped with a functioning antiskid braking system than for airplanes without such a system.
(1) For airplanes without an antiskid system, brakes should be applied progressively throughout the deceleration process, and the pilot must recognize the point that wheel skid occurs. Maximum braking effectiveness occurs just prior to the point where wheel skidding occurs. However, should a skid occur, releasing brake pressure can stop skidding and then maximum braking can be reestablished until the deceleration process is completed. Pilots should be aware that a skid is most likely at higher speeds and at that point may not be perceptible.
(2) For airplanes with antiskid system, to achieve the benefits of antiskid, the brakes must be applied firmly throughout the deceleration process. When maximum braking is required, it is accomplished by holding maximum brake application pressure and allowing the antiskid system to operate. Letting up on the brakes (unless required to regain directional control) defeats the purpose of the antiskid system. The pulsation caused by the modulation of the brake pressure by the antiskid system indicates that the antiskid system is operating normally although the pulsation may be disconcerting to the pilot.
g. Touchdown Technique. A firm touchdown at the target touchdown point, followed by, for those airplanes so equipped, the deployment of ground spoilers, the timely selection of thrust reverse (if installed), and the application of max/progressively applied firm braking will result in the shortest landing distance ground roll, particularly on wet or contaminated runway surfaces.
h. Directional Control. The nosewheel should be lowered onto the runway immediately after touchdown. Placing the nosewheel on the runway will assist in maintaining directional control. It also decreases the wing angle of attack, thereby decreasing lift and placing more load onto the tires, which increases tire-to-ground friction.
Appendix 1
i. Thrust Reversers. In the event of an asymmetric deployment, the nosewheel on the ground will aid in directional control. If the thrust reversers deploy asymmetrically, or if the airplane begins to drift due to a crosswind, close the thrust reversers and reestablish directional control. Once the airplane’s track down the runway is reestablished, redeploy the thrust reversers. Use airplane steering in accordance with the AFM procedures.
6. SUMMARY. A stabilized approach terminating with a landing in the TDZ, timely deployment of airplane deceleration devices, and braking technique are critical elements to mitigating the landing runway-overrun risk. It is a responsibility of operators to consider the factors presented, and incorporate these items, as well as the extensive research and safety information available regarding avoiding a runway overrun into training programs and operations manuals. It is the pilot’s responsibility to apply the landing assessment process, exercise conservative aeronautical decision-making (ADM), be proficient in the landing techniques for the conditions to be encountered, and that a go-around or diversion are mitigations to prevent a runway overrun.
Appendix 2 APPENDIX 2. REGULATORY CONSIDERATIONS AND RECOMMENDED
OPERATIONAL PRACTICES
1. REGULATORY REQUIREMENTS FOR LANDING FOCUS ON PREDEPARTURE FLIGHT PLANNING. The intent is to ensure that a flight operation does not begin that cannot reasonably be safely concluded upon reaching the destination or alternate airport, as applicable.
Regarding regulations, there are differences in the various operating regulations concerning landing performance. Compliance with these regulations is shown using approved data from the Airplane Flight Manual (AFM).
NOTE: Some manufacturers supply advisory or supplemental data that provides landing performance data based on landing weight, airport elevation and temperature, corrected for wind (headwind, tailwind), and slope. Manufacturers may also supply advisory or supplemental data that accounts for runway condition (wet, dry, and contaminated) and braking degradation (i.e., antiskid is inoperative, thrust reversers are inoperative, etc.). Pilots and operators should be familiar with the data presented in their AFM, and they should be capable of applying both the approved data and advisory or supplemental data to make operational decisions.
2. REGULATORY CONSIDERATIONS. It is not the intent of this advisory circular (AC) to provide the regulatory requirements. However, operators and pilots must be knowledgeable of the operational regulations applicable to their type of operation. Figure 2-1, Sections 121.195(b),
135.385(b), and 91.1037(b) 60-Percent Rule; Figure 2-2, Sections 121.195(d), 135.385(d), and
91.1037 Wet Runway 115-Percent Rule; and Table 2-1, Regulatory Planned Landing Distance Calculations Overview, provide a regulatory overview of airplane landing performance requirements applicable to flight operations conducted in accordance with Title 14 of the Code of Federal Regulations (14 CFR) parts 91K, 121, and 135.
FIGURE 2-1. SECTIONS 121.195(B), 135.385(B), AND 91.1037(B) 60-PERCENT RULE
Appendix 2 NOTE: Part 91, § 91.1037 states, in part: “(e) Unless, based on a showing of actual operating landing techniques on wet runways, a shorter landing distance (but never less than that required by paragraph (b) or (c) of this section) has been approved for a specific type and model airplane and included in the Airplane Flight Manual, no person may take off a turbojet airplane when the appropriate weather reports or forecasts, or any combination of them, indicate that the runways at the destination or alternate airport may be wet or slippery at the estimated time of arrival unless the effective runway length at the destination airport is at least 115 percent of the runway length required under paragraph (b) or (c) of this section.”
FIGURE 2-2. SECTIONS 121.195(D), 135.385(D), AND 91.1037 WET RUNWAY 115-PERCENT RULE
NOTE: Calculations depicted in Table 2-1 are preflight planning calculations. When the flight arrives at the destination, 100 percent of the effective runway length is available for landing. It should be noted that operators with operations specifications (OpSpecs) and management specifications (MSpecs) must complete these calculations in accordance with those directives.
1.67 / Factor 1.97 Page 2
Appendix 2 TABLE 2-1. REGULATORY PLANNED LANDING DISTANCE CALCULATIONS
OVERVIEW Regulation Type of Airplane Runway Condition Percentage of Effective Runway Length § 121.195(b) § 135.385(b) § 91.1037(a) Large turbine powered Dry 60 percent § 121.195(c) § 135.385(c) Turbopropeller alternate airport Dry 70 percent § 121.195(d) § 135.385(d) § 91.1037(e) Turbojet without an approved AFM wet runway landing technique Wet/Slippery 115 percent of § 121.195(b) or § 135.385(b), or § 91.1037(e) AFM factored dry landing distance § 135.385(f) § 91.1037(c)(2) Large turbine powered, eligible on demand OpSpecs/MSpecs Authorized 80 percent § 121.197 § 135.387(a) Large turbine powered alternate airport Dry 60 percent § 121.197 § 135.387(a) Turbopropeller alternate airport Dry 70 percent § 135.387(b) § 91.1037(3)(d) Large turbine powered, eligible on demand alternate airport OpSpecs/MSpecs Authorized 80 percent NOTE: For part 125 operators, it is highly recommended that they adopt the stated regulatory requirements contained in Table 2-1 above.
a. Part 91 Operational Recommendations.
(1) Preflight planning requirements for part 91 operators are governed by §§ 91.103 and 91.605. It is highly recommended that part 91 operators, and pilots calculate predeparture landing distance performance requirements based on the guidance contained in their AFM, and employ the landing assessment process before initiating the approach landing phase of the flight, and consider the factors presented in this AC to avoid a runway overrun.
(2) To ensure that an acceptable landing distance safety margin exists at TOA, the FAA recommends a 15 percent safety margin be applied to the actual airplane landing distance. The 15 percent safety margin is a minimum safety margin to be applied after accounting for all known variables, such as the meteorological, runway surface conditions, landing with a tailwind, airplane configuration and weight, runway slope, threshold crossing height and airspeed, and the timely utilization of ground deceleration devices. Be prepared, know the landing conditions, divert to an alternate, or go around, but do not risk a runway overrun.
Page 3 (and 4)
Appendix 3 APPENDIX 3. OPERATIONAL AWARENESS OF WET AND CONTAMINATED
RUNWAYS LANDING DISTANCE DATA
1. MANUFACTURERS AND AIRPLANE FLIGHT MANUAL (AFM) DATA. In accordance with Federal Aviation Administration (FAA) certification rules, the FAA-approved AFM data are determined only for dry runway conditions. Some manufacturers provide supplemental FAA-approved AFM data for operation on wet grooved runways. Manufacturers may also provide supplemental advisory landing distance data for conditions beyond those required by regulation; however, they are not used in lieu of the advised 15 percent safety margin. The data contained in these supplements, although not FAA approved, are based on the same flight test data used to generate the FAA-approved dry runway takeoff and landing performance presented in the AFM. Performance is calculated using analytical corrections to dry runway performance utilizing methods appropriate for aircraft certification outside the United States. Again, at least a 15 percent safety margin should be applied to these data.
2. METHODS USED TO ADJUST DRY RUNWAY PERFORMANCE. The analytical methods employed to adjust the dry runway performance to account for conditions encountered on wet and contaminated runways are complex and comprehensive. The methods utilized include adjustments for changes in the braking coefficient, precipitation drag, and hydroplaning, as applicable.
3. BRAKING COEFFICIENT. The braking coefficient is a measure of the braking efficiency at the contact point between the airplane main tires and the runway. The braking coefficient is the ratio of braking force divided by the weight on the tire. A tire supporting 5,000 pounds with a braking coefficient of 0.5 would be capable of producing 2,500 pounds of stopping force. As contaminants are introduced onto the runway, the braking coefficient is reduced, decreasing the stopping capability of the airplane.
NOTE: For example, a wet runway typically will reduce the braking coefficient by about 50 percent. Runways contaminated with dry snow typically can reduce the braking coefficient down to about 0.10, or only 20-25 percent of the braking capability of a dry runway. In other words, the 2,500-pound stopping force on a dry runway may now be only 500-600 pounds on dry snow.
4. PRECIPITATION DRAG. Precipitation drag comprises two components: precipitation impingement drag and precipitation displacement drag.
a. Precipitation Impingement Drag. Precipitation impingement drag is the force created as contaminant spray from the tires impacts parts of the airframe, such as the flaps behind the main gear. Impingement drag assists in slowing the airplane and resists acceleration.
b. Precipitation Displacement Drag. Precipitation displacement drag is a resistance force created as the tires push runway contaminant out of the way while moving along the runway.
c. Example. It is the force you feel when trying to move your hand rapidly through water.
As your hand moves the water is forced out of the way, and the faster you try to move your hand, the stronger the resistance. Runway contaminants act much the same way. The resultant Page 1
Appendix 3 resistance force assists in slowing the airplane during landing or a rejected takeoff, and also resists acceleration during takeoff.
NOTE: Some manufacturers do not include the effects of precipitation drag on landing distances. However, if the effect of precipitation drag is included in the landing distance performance for the airplane, it has the non-intuitive characteristic. This means that given a conservative approach to assessing the airplane’s landing distance due to precipitation drag, if a deeper contaminant level is selected with the intention of being conservative, the result will be the opposite—it will be non-conservative. If less contaminant is actually there, it will result in a longer distance than calculated.
5. DETERMINE THE RUNWAY SURFACE CONDITION. Appropriate determination of the runway surface condition is basic to the mitigation of a runway overrun. Once the surface condition is determined, it is a pilot’s responsibility to decide whether the standard AFM dry runway performance charts are appropriate or whether the wet and contaminated performance data needs to be consulted. In preparing for takeoff, this decision is considerably easier since the pilot can visually survey the runway. The standard dry runway charts are for a totally dry runway.
NOTE: For example, if the ramp is too damp to sit on due to morning dew, the runway is probably the same. The pilot should use the wet or contaminated performance data.
6. DATA REVIEW. When reviewing takeoff and landing data, the pilot should pay attention to the details, and select the correct chart. In many cases this is obvious, but there may be conditions, or combinations of conditions, that can make the selection problematic. Careful review of Aviation Routine Weather Report (METAR) or other airport reports may provide sufficient information to make the proper selection. At airports where automated terminal information service (ATIS) is available, surface contamination reports may be included that can be used as a guide. At other airports, no information may be available. Regardless of the source, it is prudent to utilize the information that yields the most conservative performance. If reports indicate mixed runway conditions such as snow and slush, use the chart for the contaminant that results in the longest distance. If no reliable information is available, use the chart for the reasonably likely condition that provides the longest distance.
NOTE: If you choose to land with a tailwind, a tailwind is a significant factor that increases an airplane’s landing distance. Selection of a runway condition that renders a shorter distance should only be based on factual information. The pilot should resist the temptation to use a less severe runway contamination condition simply because it produces a landing distance that is equal to or less than the available runway length.
NOTE: Runway overrun mitigation implies, if the landing assessment reveals that the runway length available is not long enough to safely land and stop the airplane, change to a longer runway, or even divert to a different airport.
Appendix 3
7. RUNWAY SURFACE CONDITIONS BEYOND DATA COVERAGE. There are runway surface conditions, such as wet ice, that are worse than the wet and contaminated data provided in the airplane’s landing performance AFM. Even the most effective braking systems are ineffective in the presence of a near zero braking coefficient.
NOTE: For example, with a zero or near zero braking coefficient, the rolling friction coefficient of all the tires is near zero. Nosewheel steering will be ineffective, and the pilot will not be able to correct for any side force on the airplane, such as a crosswind. Given this reported runway condition, the flight should divert to an airport where the better landing conditions are reported.
8. OPERATIONS AT NON-TOWERED AIRPORTS. Operations at non-towered airports require pilots to gather available information on expected runway conditions prior to initiating an approach.
NOTE: For example, if there is no clear report of runway condition(s), but the pilot knows rain has been in the area, that pilot should assume the runway is wet. Also, if there is rain actively falling on the runway, standing water should be assumed. If there is any doubt as to the amount of water on the runway, assume the most conservative condition that requires the longest landing distance.
9. DECELERATION. Once committed to an operation on a wet or contaminated runway, the pilot should expect a lower level of deceleration than experienced on a dry runway.
NOTE: For example, consider the landing distances for wet and contaminated surfaces, assuming zero wind and a zero runway gradient.
Then add the distance effect of a tailwind, downhill runway gradient, additional speed, and delayed use of deceleration devices. Under these conditions, a wet runway increases the landing distance over a dry runway by approximately 26 percent. If standing water is present, the landing distance increases approximately 52 percent.
NOTE: The contaminant only affects the ground roll and braking. It has no impact on the air distance from 50 feet (ft) to touchdown, which is included in the landing distance. In the presence of standing water, for the total landing distance to increase 52 percent, the ground braking distance increases 100 percent. This situation will surprise a pilot the first time it is encountered because the deceleration rate on this surface will be only one-half of what the pilot has experienced on a dry runway.
10. CONTAMINANT PROCEDURES. For any contaminant, the pilot should expect a relatively low deceleration rate in the initial phase of braking. A wet runway may be less severe than other contaminants, but the pilot must remember that any increase in total landing distance will occur entirely in the landing ground roll braking segment.
Appendix 3 NOTE: Under some conditions, wet runways have exhibited significantly worse than expected braking, and the reason for this is not yet understood.
11. HYDROPLANING. Hydroplaning is defined as a condition that exists when the tires ride on the surface of the contaminant, much like a water ski. When the tires are hydroplaning, directional control and braking action are virtually impossible. An effective antiskid system can minimize the effects of hydroplaning. See Figure 3-1, Hydroplaning.
FIGURE 3-1. HYDROPLANING
a. Hydroplaning. Hydroplaning is a significant factor that should be considered in determining stopping capability on a contaminated runway. Hydroplaning depends on wheel speed and tire pressure. The key item to remember when the airplane is hydroplaning is that the tires are no longer in contact with the runway, although the airplane is not airborne.
Though at high speeds, aerodynamic drag can provide a significant decelerating force. Reverse thrust/propeller reversing, if installed, provides nearly all the decelerating force when hydroplaning since the brakes are essentially ineffective. These characteristics are included in the distances presented in the contaminated runway supplemental data when provided by the airplane manufacturer.
b. Directional Control. It is very important to realize that directional control has not been demonstrated on these surfaces. The pilot should expect significant degradation in directional controllability on a contaminated runway, depending on the level of available runway friction, especially with an engine shut down or with a crosswind. Some manufacturers provide maximum crosswind values, derived through simulation and calculation, for landing on contaminated runways.
NOTE: Runway surface conditions are rarely consistent over the full length of the runway. Even dry runways will present different friction coefficients due to heavy rubber deposits in the touchdown zone (TDZ) and large paint markings such as the 1,000-foot markers or centerline stripes. The degree of runway surface contamination due to ice, packed snow, or standing water varies along the length of the runway. The pilot will sense changes in the deceleration rate as the airplane transitions from one contaminant condition to another.
Appendix 3
12. BRAKE FAILURE VERSUS REDUCED BRAKING. How does the pilot differentiate between reduced braking capability and a brake failure with reduced, and occasionally very low, deceleration rates due to runway contamination? The best answer is for the pilot to be thoroughly familiar with all operating characteristics of the airplane. Experience is the best tool, and until the pilot has the experience, training and knowledge of aircraft performance is the best tool. All pilots should take advantage of the opportunity to experience braking capability in the simulator on different contaminants when possible. While decelerating, scan the airspeed display in order to relate the change in speed to the kinesthetic perceptions. During the period of maximum brake application after touchdown, the antiskid system is working to keep the tires on the verge of a skid. The pilot may perceive small, abrupt pulses as the tires occasionally get a solid grip prior to skidding, followed by a short release of brakes to allow the tires to spin up again. As the surface condition becomes more challenging, the antiskid system will command longer brake releases to maintain a proper level of friction between the tire and the runway. As the airplane decelerates, the braking effectiveness will increase but may never attain dry runway levels. As long as the pilot senses the cycling of the antiskid system, the pilot knows the brakes are performing to the maximum extent permitted by the runway surface condition.
NOTE: The pilot cannot modulate the brakes better than the antiskid system. Pilot response time to the changing conditions is measured in seconds, and the antiskid system can adjust in milliseconds. The best braking performance will occur when the pilot presses hard on the brake pedals and maintains a constant pressure. Let the antiskid do all the modulation but be sensitive to that same antiskid operation. Be perceptive and make note of the antiskid pulses. That is the pilot’s firsthand knowledge of proper brake operation.
13. PERFORMANCE DATA NOTES. Every pilot should read and understand the information presented in the contaminated runway supplemental data before using the information to calculate performance. When the pilot thoroughly understands the operation of the antiskid system, becomes familiar with the runway condition at the destination, and completes and applies conservative landing distance calculations, the pilot will mitigate the risk of a runway overrun.
14. TABLES FOR RUNWAY MITIGATION. These tables are included to assist the pilot in the application of the concepts presented to mitigate the risks associated with the hazard of a runway overrun. Table 3-1, Memory Jogger: Can You Stop?; Table 3-2, All Factors Present Cumulative Landing Distance Example; and Table 3-3, All Factors Cumulative Landing Distance Example Stabilized Approach and Timely Deceleration, provide guides to be considered in order to mitigate a runway overrun. Table 3-1 provides a memory jogger for the concepts pilots must exercise to mitigate the risk of a runway overrun. Table 3-2 provides a sample of what can occur if all the runway factors to consider are present in a landing. Table 3-3 demonstrates the benefits of a stabilized approach, choosing to land with favorable winds, and timely deceleration.
NOTE: These items cannot replace the information contained in the AFM.
They are provided to help the flightcrew member recognize the possible increase in risk associated with certain conditions. The information Page 5
Appendix 3 presented in this AC must not be used to replace or supplant AFM landing performance or associated contaminated runway performance information provided by the manufacturer.
TABLE 3-1. MEMORY JOGGER: CAN U STOP?
CAN U STOP?
C–Calculate Use the manufacturer’s or company data to determine the landing distance required prior to departure and again prior to landing based on company SOPs. Be sure to consider factors as dry/wet runways and associated contamination, planned touchdown point, speed and height over the landing threshold, runway slope, tailwind/wind speed and direction, inoperative equipment, and any special cases.
U–Understand The manufacturer’s AFM landing data and it is derived based on flight test data. Factors to be applied to the data to adjust it for the current conditions. If data is not available, employ the information contained in SAFO 06012.
S–Stabilized Ensure that you understand all the requirements of a stabilized approach and you are able to fly one given the actual conditions. If not, go around!
P-Professional Land like a professional using the airplane’s capabilities as described in the AFM and SOPs.
A professional puts safety ahead of style.
Appendix 3 TABLE 3-2. ALL FACTORS PRESENT CUMULATIVE LANDING DISTANCE
EXAMPLE
1. Available runway length. 5,000 ft
2. Per AFM, Dry runway Un-factored AFM landing distance for density altitude & lightest landing gross weight. 3,000 ft
3. Runway Slope -1%: Add 10% of landing distance per 1% downhill slope, i.e., 1% downhill slope adds 10% to the landing distance.
300 (3,300’)
4. Excessive airspeed at 50 foot landing threshold, landing distance increase: For each 10% increase in landing speed greater than the AFM, add 20% landing distance or:
Example: 10 % fast (3,300 × .20 = 660 ft).
660 ft (3,960’)
5. Tailwind Condition: Add 21% to landing distance for each 10 kts in tailwind.
Example: 10-kt Tailwind .21 × 3,960 = 832 ft.
832 ft (4,792’)
6. Extended Flare Add 200 ft per second flare time:
Results in a 200 ft/sec additive (2 × 200 = 400 ft). 400 ft (5,192’)
7. Excess 50-ft height: Add 200 ft to the landing distance for each 10 ft above 50 ft.
Example: 10-ft excess.
200 ft (5,392’)
8. MEL/CDL additions: Any additions caused by minimum equipment list (MEL)/Configuration Deviation List (CDL) requirements No MEL/CDL additive 0 ft.
9. Sum of before landing items 2 through 8 added 2,392 ft = 80% greater than 3,000 ft. 5,392 ft
10. Deceleration devices, 3 second deployment time.
(1 second more than the 2 second max) add 200 ft per each second greater than 2 seconds.
Add 200 ft or use AFM data if available.
200 ft (5,592’)
11. Less than maximum braking add 20% or use AFM data if available. 1,118 ft (6,710’)
12. Wet Runway SAFO Safety Margin.
If wet, add 15 percent of line 9 or use AFM data if available .15 × 5,392 = 809 ft.
1,107 ft (7,717’)
13. After landing factors, Lines 10 - 13 added 2,425 ft, 45% greater than 5,392 ft. Required landing distance 7,717 ft 2,717 ft longer than available.
Cumulative Landing Distance Increase: 157% 7,717 ft Page 7