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LANDING PERFORMANCE The performance data for takeoff and landing an aircraft can be obtained from the aircraft's flight manual or pilot's operating handbook. The actual performance of an aircraft is affected by many variables which must be taken into account.
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LANDING CONSIDERATIONS
Factors to Consider: Aircraft Gross Weight Available Engine Thrust Field Elevation Pressure Altitude Temperature Winds Runway Length Runway Slope Runway Condition Terrain & Obstacles MEL/CDLs Icing The weight of an aircraft is one of the basic factors that determines the length of the landing roll of an aircraft. An increase in weight increases the stall speed of an aircraft. Stall is a reduction in the lift coefficient generated by a wing as angle of attack increases. Therefore, the minimum approach speed is much higher in case of heavier aircraft's. The kinetic energy that has to be overcome to stop an airplane, is a function of the mass of the airplane and the square of the speed at touchdown. The kinetic energy in case of heavier aircraft's is higher and the brakes have to absorb this greater energy, increasing the landing run of an aircraft. A decrease in density of air results in decrease in both aircraft and Engine performance. High elevation airports are characterized by low pressure and high ambient temperatures. The TAS will be higher than the Indicated airspeed indicated by the Airspeed indicator to the pilot in air of low density. This increase in TAS leads to greater touchdown speed hence increases the landing roll. More energy has to be absorbed by the brakes thus demanding the need of a longer runway. An increased density altitude means a longer landing distance. The headwind reduces the landing distance for an aircraft. Landing into a headwind reduces the GS for the same TAS. This is beneficial to both, the pilots as well as the Air traffic controllers (ATC). An aircraft landing into a headwind will require lesser runway and will be able to vacate the runway sooner. If the headwind decreases near the ground, there's a decrease in the performance of the aircraft and it will tend to sink and possibly under shoot the aiming point. Tailwind increases the Ground Speed of an aircraft for the same TAS and thus a longer runway distance will be required for an aircraft to land. Landing in a tailwind situation could lead to a stall because of the tendency of the pilot to reduce the airspeed while landing. Also, there's a chance of over shooting the runway and colliding with objects or terrain.
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LANDING The Maximum Landing Weight (MLW) is computed by finding the most restrictive (lowest weight) of the following: 1. Landing Runway Limit Weight (Performance) 2. Landing Climb Limit Weight (Performance) 3. Structural Landing Limit Weight (Structural) The Landing Climb Limit Weight is also known as a go-around scenario. Calculate all three and use the lower number.
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LANDING The regulations require specific operational limitations for stopping on the landing runway, or initial climb away from the runway during a missed approach. Weight planning and establishing weight limitations for the aircraft allows the airline to ensure the aircraft meet these requirements depending on ambient conditions. Separate weight limitations are created for the Runway (the Landing Runway Limit Weight) to cover touchdown and stopping, and for the Climb (the Landing Climb Limit Weight), which covers a missed approach or “go-around” situation. This data is found in the Runway Analysis Manual.
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LANDING RUNWAY LIMIT WEIGHT
The Landing Runway Weight must be such that a full stop landing can be made at the destination or alternate airport within 60% of the effective length of the runway from a point 50 feet above the runway threshold at a speed no less than 1.3 Vso. Low visibility and wet runways each require an additional 15% margin above the 60% of the effective distance of the runway. The runway length required for landing is based on a full spoiler extension, anti-skid brakes, and flaps fully down throughout the landing roll. Reverse thrust is not considered. It results in only about 300 ft less runway in dry conditions.
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LANDING SPEEDS VS (Stall Speed)
Vs – stalling speed or the minimum steady flight speed at which the airplane is controllable. VSO (Stall Speed-Landing Configuration) Vso – stalling speed or the minimum steady flight speed in the landing configuration. VREF (Reference Speed) Vref – reference speed, it is normally 1.3 x Vso. Three ways of slowing/stopping Reverse thrust, Aerodynamic braking, wheel brakes Jeppesen computes V1 for its customers based on the worst performing jet aircraft is use – the B with the smaller engines. They guarantee that if your pilots reject at or after V1, that they will clear all obstacles on departure as their aircraft will out perform a B
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RUNWAY CONDITIONS Dynamic Hydroplaning
Occurs when a tire rolls through standing water, forms a bow wave then rolls up on top of the wave losing contact with rwy Rule of Thumb: 9 x square root of tire pressure Viscous Hydroplaning Occurs when there is a thin film o water covering a smooth surface such as paint or rubber-coated portion of runway. Occurs much lower speed than Dynamic Hydroplaning. Reverted Rubber Hydroplaning Occurs during a locked wheel skid. Water trapped between tire and rwy is heated by friction, tire rides on pocket of steam. Jeppesen computes V1 for its customers based on the worst performing jet aircraft is use – the B with the smaller engines. They guarantee that if your pilots reject at or after V1, that they will clear all obstacles on departure as their aircraft will out perform a B
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LANDING RUNWAY LIMIT WEIGHT
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LANDING CLIMB WEIGHT(S)
The Landing Climb Limit Weight ensures compliance with both the Approach Climb and Landing Climb requirements. Approach Climb Performance (go-around or balked landing). The approach climb gradient is based on an engine inoperative, the aircraft at maximum certified landing weight, landing gear retracted, approach flaps set, and takeoff thrust on the remaining engine(s). The demonstrated climb gradient must be at least 2.1%. Landing Climb Performance (go-around or balked landing). The landing climb gradient is based on all engines operating at takeoff thrust, full landing flaps deployed, landing gear extended, and the aircraft at maximum certificated landing weight. The gradient must be at least 3.2%.
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LANDING CLIMB WEIGHT(S)
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LANDING DATA CONSIDERATIONS
Landing (Runway) The 60% requirement is pre-dispatch ONLY and in the case of an in-flight emergency, the full length of the runway can be considered for stopping, using the judgment of the captain and dispatcher considering the current conditions at that airport. Go-Around (Climb) The length of the runway has no effect on the missed approach limitations of the aircraft as this is an in-flight consideration only. The requirement is for positive climb only; terrain clearance is not considered.
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AIRPORT/RUNWAY ANALYSIS
Prepared by independent companies (Jeppesen, AeroData, etc.) or the airline Engineering Department to provide suitable performance data for takeoff and landing. Combines Airplane Flight Manual (AFM) performance during certification with extensive and thorough runway and obstacle data. Considers TERPS (Terminal Procedures) such as SIDs, Departure Procedures (DPs) and Obstacle Departure Procedures (ODPs). Airlines can create specific, ad-hoc procedures to avoid obstacles and maintain FAA performance requirements. Not all airlines have their own engineering departments to compute these numbers. Many use vendors such as Jeppesen, AeroData, etc.
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AIRPORT/RUNWAY ANALYSIS
Considers loss of climb performance in turns. Looks at terrain up to 30 miles or farther from the departure airport. Ensures the aircraft will not exceed brake energy limits, tire speed limits, etc. Aids in maximizing payload uplift. Can account for runway construction or other shortened distances. Usually exceeds 14 CFR Part 121 and AC requirements to enhance safety.
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AIRPORT/RUNWAY ANALYSIS
Landing ASO Anti-Skid Operative - Dry Runway ASI Anti-Skid Inoperative - Dry Runway ASO WET Anti-Skid Operative - Wet Runway ASI WET Anti-Skid Inoperative - Wet Runway The Ops Manual and Ops Specs for some airlines with smaller jets allow the operator to consider a wet runway to be dry for performance planning if the runway is grooved (Comair). Larger jet transports, for the most part, do not utilize this, for safety reasons.
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ENGINE-OUT PROCEDURES
VMC (Minimum Control Speed) Vmc – minimum control speed with the critical engine inoperative. Vmc will vary with aircraft’s CG, Vmc will be higher with the CG at its most rearward-allowed position. VXSE (Angle of Climb Speed) Vxse – best single engime angle-of-climb speed. VYSE (Rate of Climb Speed) Vyse – best single engine rate-of-climb speed. Jeppesen computes V1 for its customers based on the worst performing jet aircraft is use – the B with the smaller engines. They guarantee that if your pilots reject at or after V1, that they will clear all obstacles on departure as their aircraft will out perform a B
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ENGINE-OUT PROCEDURES
VXSE Best angle of climb speed The greatest gain in altitude over a given horizontal distance. VYSE Best rate of climb speed The greatest gain in altitude over a given amount of time.
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ENGINE OUT FERRY FLIGHTS
A three or four engine turbine powered airplane may be ferried to a maintenance base with one engine inoperative if the following requirements are met: 1. Airplane model must have been test flown to show ops safe 2. Approve flight manual must contain performance data 3. Operating weight limited to minimum required for flight 4. Takeoffs are usually limited to dry runways 5. Computed T/O performance must be within acceptable limits 6. Initial climb cannot be over thickly-populated areas 7. Only required flight crewmembers may be on aircraft 8. WX conditions at T/O and Dest airports must be VFR The Landing Climb Limit Weight is also known as a go-around scenario. Calculate all three and use the lower number.
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