AC Perfomance Landing Performance PDF

Getting to Grips with Aircraft Performance LANDING E. LANDING 1. INTRODUCTION To dispatch an aircraft, an operator has to verify landing requirements based on airplane certification (JAR 25 / FAR 25) and on operational constraints defined in JAR-OPS...

Getting to Grips with Aircraft Performance LANDING E. LANDING 1. INTRODUCTION To dispatch an aircraft, an operator has to verify landing requirements based on airplane certification (JAR 25 / FAR 25) and on operational constraints defined in JAR-OPS and FAR 121. In normal operations, these limitations are not very constraining and, most of the time authorize dispatch at the maximum structural landing weight. This leads to a minimization of the importance of landing checks during dispatch. However, landing performance can be drastically penalized in case of inoperative items, adverse external conditions, or contaminated runways. Flight preparation is, therefore, of utmost importance, to ensure a safe flight. In the next chapters, we will specify landing requirements based on airworthiness rules, and dispatch conditions. A final chapter will address the flight management and the choice of a diversion landing airport. 2. LANDING DISTANCE AVAILABLE (LDA) 2.1. With no Obstacle under Landing Path In this case, the Landing Distance Available (LDA) is the runway length (TORA). The stopway cannot be used for landing calculation. Landing Distance Available (LDA) Figure E1: Landing Distance Available 2.2. With Obstacles under Landing Path The landing distance available (LDA) may be shortened, due to the presence of obstacles under the landing path. Annex 8 of ICAO recommendations specifies the dimension of the protection surfaces for landing and approach (Approach funnel). When there is no obstacle within the approach funnel, as defined below (see Figure E2), it is possible to use the runway length to land. 111 LANDING Getting to Grips with Aircraft Performance 15% 300 m Runway approach surface 60 m Figure E2 : Approach Surface However, if there is an obstacle within the approach funnel, a displaced threshold is defined considering a 2% plane tangential to the most penalizing obstacle plus a 60 m margin (Figure E3). Obstacle influence on LDA Displaced threshold 2% 60 m LDA Figure E3: Displaced Threshold In this case, the Landing Distance Available (LDA) is equal to the length measured from the displaced threshold to the end of the runway. 3. LANDING PERFORMANCE 3.1. Operating Landing Speeds Originally, the speeds defined in next chapters were manufacturer or operator operating speeds. Today, most of them (as the term VREF the reference landing speed for example) are widely used and understood operationally. The JAR authorities found it convenient to use the same terminology in stating airworthiness requirements and have, indeed, been used in recent requirement amendments. 112 Getting to Grips with Aircraft Performance LANDING 3.1.1. Lowest Selectable Speed: VLS As a general rule, during flight phases, pilots should not select a speed below VLS (Lowest Selectable Speed), defined as 1.23 VS1g of the actual configuration. VLS = 1.23 Vs1g g * The 1.23 factor is applicable to the fly-by-wire aircraft (1.3 for the others). This rule applies for landing. During landing, pilots have to maintain a stabilized approach, with a calibrated airspeed of no less than VLS down to a height of 50 feet above the destination airport. 3.1.2. Final Approach Speed: VAPP VAPP is the aircraft speed during landing, 50 feet above the runway surface. The flaps/slats are in landing configuration, and the landing gears are extended. VAPP is limited by VLS: VAPP ≥ VLS It is very common to retain a margin on VLS to define VAPP. For Airbus aircraft, in normal operations, the VAPP is defined by: VAPP = VLS + wind correction Wind correction is limited to a minimum of 51 knots, and a maximum of 15 knots. VAPP is displayed on MCDU APPRoach page. The FMGS and managed speed is used to define the VAPP TARGET. It gives efficient speed guidance in approach with windy conditions, since it represents: VAPP TARGET = GS mini + actual headwind GS mini = VAPP – Tower wind Actual headwind is measured by ADIRS, and the tower wind is entered on the MCDU. 1 When the auto-thrust is used or to compensate for ice accretion on the wings 113 LANDING Getting to Grips with Aircraft Performance 3.1.3. Reference Speed: VREF In case of failure in flight, emergency or abnormal configuration, performance computations are based on a reference configuration and on a reference speed. VREF means the steady landing approach speed at the 50 feet point for a defined landing configuration. For Airbus, this configuration is CONF FULL. That gives: VREF= VLS in CONF FULL In case of a system failure affecting landing performance, Airbus operational documentation indicates the correction to be applied to VREF to take into account the failure: VAPP = VREF + ∆VINOP Another speed increment can be added to VAPP to account for wind, when needed. 3.2. Actual Landing Distance (ALD) JAR 25.125 Subpart B FAR 25.125 Subpart B 3.2.1. Manual Landing “JAR/FAR 25.125 (a)The horizontal distance necessary to land and to come to a complete stop from a point 50 ft above the landing surface must be determined (for standard temperatures, at each weight, altitude and wind within the operational limits established by the applicant for the aeroplane) as follows: The aeroplane must be in the landing configuration A stabilized approach, with a calibrated airspeed of VLS must be maintained down to the 50 ft.” During airplane certification, the actual landing distance is demonstrated as follows: It is the distance measured between a point 50 feet above the runway threshold, and the point where the aircraft comes to a complete stop. To determine this actual landing distance, several conditions must be achieved: Standard temperature Landing configuration 114 Getting to Grips with Aircraft Performance LANDING Stabilized approach at VLS (or VMCL whichever is greater) for the configuration for manual landing. Non excessive vertical acceleration Determination on a level, smooth, dry, hard-surfaced runway Acceptable pressures on the wheel braking systems Braking Means other than wheel brakes: Spoilers, reversers (except on dry runway), can be used when they are safe and reliable. Actual landing distance is also certified with degraded braking means (spoiler inoperative, one brake inoperative…). V ≥ 1.23 V S braking action V =0 50 ft A ctual L anding D istance Figure E4: Actual Landing Distance Actual Landing Distances are certified on dry runways for all Airbus aircraft, certified on contaminated and icy runways for all fly-by-wire aircraft and published (for information) for wet. Demonstrated landing distances will not account for reversers on dry runways. The reverse thrust influence may be considered on contaminated runways. On dry runways, landing distances are demonstrated with standard temperatures, according to JAR/FAR 25. However, on contaminated runways, Airbus decided to take into account the influence of temperature on landing distance demonstration. This choice ensures added safety as it gives a conservative ALD. Landing distance data must include correction factors for no more than 50% of the nominal wind components along the landing path opposite to the landing direction, and no less than 150% of the nominal wind components along the landing path in the landing direction. This is already taken into account in published figures and corrections. 115 LANDING Getting to Grips with Aircraft Performance 3.2.2. Automatic Landing JAR AWO The required landing distance must be established and scheduled in the airplane Flight Manual, if it exceeds the scheduled manual landing distance. On a dry runway, the ALD in autoland is defined as follows: ALD = (Da + Dg) Where : Da is the airborne phase distance Dg is the ground phase distance. Airborne phase = Da 50 ft d1 d2 3xσd2 Threshold 0 Figure E5 : Airborne Phase The airborne phase Da is the distance from the runway threshold up to the glideslope origin (d1), plus the distance from the glideslope origin up to the mean touchdown point (d2), plus three times the standard deviation of d2 (σd2). The distance from the glideslope origin to the mean touchdown point (d2), as well as its corresponding standard deviation (σd2), have been statistically established from the results of more than one thousand simulated automatic landings. Ground phase = Dg 50 ft VTD =VTD + 3σ VTD Threshold 0 Figure E6 : Ground Phase The Ground Phase Dg for an automatic landing is established as with a manual landing, assuming a touchdown speed equal to the mean touchdown speed (VTD) plus three times the standard deviation of this speed (σVTD). 116 Getting to Grips with Aircraft Performance LANDING 3.3. Go-Around Performance Requirements A minimum climb gradient must be observed, in case of a go-around. The minimum air climb gradients depend on the aircraft type. 3.3.1. Approach Climb JAR 25.121 Subpart B FAR 25.121 Subpart B This corresponds to an aircraft’s climb capability, assuming that one engine is inoperative. The “approach climb” wording comes from the fact that go-around performance is based on approach configuration, rather than landing configuration. For Airbus fly-by-wire aircraft, the available approach configurations are CONF 2 and 3. 3.3.1.1. Aircraft Configuration One engine inoperative TOGA thrust Gear retracted Slats and flaps in approach configuration (CONF 2 or 3 in most cases) 1.23 VS1g ≤ V ≤ 1.41 VS1g and check that V ≥ VMCL 3.3.1.2. Requirements The minimum gradients to be demonstrated: Approach Climb Minimum Twin 2.1% climb gradient one engine out Quad 2.7% (N-1) engine(s) TOGA thrust gear retracted approach configuration 1.23 VS1g   ≤ V ≤ 1.41 VS1g VMCL  minimum gradient: 2- engine aircraft: 2.1% 4- engine aircraft: 2.7% Figure E7: Minimum Air Climb Gradients - Approach Climb 117 LANDING Getting to Grips with Aircraft Performance An approach configuration can be selected, as long as the stall speed VS1g of this configuration does not exceed 110% of VS1g of the related “all-engines-operating“ landing configuration. 3.3.2. Landing Climb JAR 25.119 Subpart B FAR 25.119 Subpart B The objective of this constraint is to ensure aircraft climb capability in case of a missed approach with all engines operating. The “Landing climb” wording comes from the fact that go-around performance is based on landing configuration. For Airbus FBW, the available landing configurations are CONF 3 and FULL. 3.3.2.1. Configuration N engines Thrust available 8 seconds after initiation of thrust control movement from minimum flight idle to TOGA thrust Gear extended Slats and flaps in landing configuration (CONF 3 or FULL) 1.13 VS1g ≤ V ≤ 1.23 VS1g and check that V ≥ VMCL. 3.3.2.2. Requirements The minimum gradient to be demonstrated is 3.2% for all aircraft types. N engines TOGA thrust gear extended landing configuration 1.13 VS1g   ≤ V ≤ 1.23 VS1g VMCL  minimum gradient: 3.2% Figure E8: Minimum Air Climb Gradients - Landing Climb For all Airbus aircraft, this constraint is covered by the approach climb requirement. In its operational documentation (FCOM), Airbus publishes the maximum weight limited by the approach climb gradient only. Landing climb performance is found in the AFM. 118 Getting to Grips with Aircraft Performance LANDING 3.4. External Parameters Influence 3.4.1. Pressure Altitude Approach speed is equal to 1.23 VS1g. But, the corresponding TAS increases with the pressure altitude. PA Ê Ö ρ Ì Ö TAS Ê Consequently, the landing distance will also increase. TOGA thrust, used for go-around, decreases when pressure altitude increases. PA Ê ⇒ engine thrust Ì Therefore, in the event of a go-around, a decrease in engine thrust implies a decrease in the air climb gradients, which means that: landing distance Ê  PA Ê ⇒  air climb gradients Ì  3.4.2. Temperature Engine thrust decreases when the temperature passes the reference temperature. Therefore, in case of a go-around, the air climb gradients will decrease. Temp Ê ⇒ go-around air climb gradients Ì 3.4.3. Runway Slope JAR-OPS 1.515 (b) Subpart G From a performance standpoint, an upward slope improves the aircraft’s stopping capability, and, consequently, decreases landing distance. Upward slope ⇒ Landing distance Ô Downward slope ⇒ Landing distance Ò 119 LANDING Getting to Grips with Aircraft Performance 3.4.4. Runway Conditions The definition of runway conditions is the same as for takeoff. When the runway is contaminated, landing performance is affected by the runway’s friction coefficient, and the precipitation drag due to contaminants. Friction coefficient Ô ⇒ Landing distance Ò Precipitation drag Ò ⇒ Landing distance Ô Depending on the type of contaminant and its thickness, landing distance can either increase or decrease. So, it is not unusual to have a shorter ALD on 12.7 mm of slush than on 6.3mm. 3.4.5. Aircraft Configuration 3.4.5.1. Engine air bleed Engine air bleed for de-icing or air conditioning, implies a decrease in engine thrust. As a result, go-around air climb gradients will decrease. Engine air bleed ON ⇒ air climb gradients Ì 3.4.5.2. Flap setting An increase in flap deflection implies an increase in the lift coefficient (CL), and in the wing surface. It is therefore possible to reduce speed such that the aircraft will need a shorter distance to land (VS1G CONF FULL < VS1G CONF 3). When wing flap deflection increases, landing distance decreases. However, when flap deflection increases, drag increases thus penalizing the aircraft’s climb performance. Landing Distance Ì Wing Flap Deflection Ê ⇒ Air Climb gradient γ % Ì When landing at a high altitude airport with a long runway, it might be better to decrease the flap setting to increase the go-around air climb gradient. 120 Getting to Grips with Aircraft Performance LANDING 4. DISPATCH REQUIREMENTS 4.1. Required Landing Distance (RLD) JAR-OPS 1.515 (c) Subpart G FAR 121.195 (b) Subpart I It is assumed “that the aeroplane will land on the most favorable runway, in still air”. Furthermore, “the aeroplane will land on the runway most likely to be assigned considering the probable wind speed and direction and the ground handling characteristics of the aeroplane, and considering other conditions such as landing aids and terrain”. Before departure, operators must check that the Landing Distance Available (LDA) at destination is at least equal to the Required Landing Distance (RLD) for the forecasted landing weight and conditions. The RLD, based on certified landing performance (ALD), has been introduced to assist operators in defining the minimum distance required at destination, and allow flight dispatch. In all cases, the requirement is : RLD ≤ LDA Operators must take into account the runway slope, when its value is greater than ± 2%. Otherwise, it is considered to be null. In the event of an aircraft system failure, known prior to dispatch and affecting the landing distance, the available runway length must at least be equal to the required landing distance with failure. This distance is equal to the required landing distance without failure multiplied by the coefficient given in the MMEL, or to the performance with failure given by the Flight Manual. 4.1.1. RLD Dry Runways JAR-OPS 1.515 (a) Subpart G FAR 121.195 and 197 Subpart I The aircraft’s landing weight must permit landing within 60% of the Landing Distance Available at both the destination and any alternate airport. That gives: RLD dry = ALD / 0.6 ≤ LDA 4.1.2. RLD Wet Runways JAR-OPS 1.520 Subpart G FAR 121.195 Subpart I If the surface is wet, the required landing distance must be at least 115% of that of a dry surface. 121 LANDING Getting to Grips with Aircraft Performance RLD wet = 1.15 RLD dry ≤ LDA A landing distance on a wet runway, shorter than that above but no less than that required on a dry runway, may be used if the Airplane Flight Manual includes specific additional information about landing distances on wet runways. This is not generally the case for Airbus aircraft. 4.1.3. RLD Contaminated Runways JAR-OPS 1.520 Subpart G For JAR operators, if the surface is contaminated, the required landing distance must be at least the greater of the required landing distance on a wet runway and 115% of the landing distance determined in accordance with approved contaminated landing distance data. ALD contaminated x 1.15 RLD contaminated = the greatest of or RLD wet For contaminated runways, the manufacturer must provide landing performance for speed V at 50 feet above the airport, such that: 1.23 VS1g ≤ V ≤ 1.23 VS1g + 10 kt In certain contaminated runway cases, the manufacturer can provide detailed instructions such as antiskid, reverse, airbrakes, or spoiler. And, in the most critical cases, landing can be prohibited. 4.1.4. RLD with Automatic Landing (DRY) Regulations define the required landing distance for automatic landing as the actual landing distance in automatic landing multiplied by 1.15. This distance must be retained for automatic landing, whenever it is greater than the required landing distance in manual mode. ALD automatic x 1.15 RLD automatic = the greatest of or RLD manual 122 Getting to Grips with Aircraft Performance LANDING 4.2. Go-Around Requirements 4.2.1. Normal Approach JAR 25.121 Subpart B FAR 25.121 Subpart B During dispatch, only the approach climb gradient needs to be checked, as this is the limiting one. The minimum required gradient is the one defined during aircraft certification (C.f. 3.3.1 Approach Climb). Operators have a choice of go-around speed (from 1.23 VS1g to 1.41 VS1g), and configuration (3 or 2) to determine the Maximum weight limited by go-around gradient. In the rare case of a go-around limitation during dispatch, operators can select CONF 2 and 1.4 VS1g for go-around calculation, and should no longer be limited. Nevertheless, even if the regulation authorizes such assumptions, it is important to warn pilots about the speed and configuration retained, as soon as they are not standard (CONF 3 and 1.23 VS1g). In a normal approach, the required climb gradient is 2.1% for twin and 2.7% for four engine aircraft, independently of airport configuration and obstacles. During dispatch, operators can account for the gradient published in the airport approach chart. 4.2.2. CAT II or CAT III Approach JAR-OPS 1.510 Subpart B & AWO 236 “JAR-OPS 1.510 (a) For instrument approaches with decision heights below 200 ft, an operator must verify that the approach mass of the aeroplane, taking into account the take-off mass and the fuel expected to be consumed in flight, allows a missed approach gradient of climb, with the critical engine failed and with the speed and configuration used for go- around of at least 2.5%, or the published gradient, whichever is the greater. The use of an alternative method must be approved by the Authority”. In case of a CAT II/III approach, the gradient is 2.5% (all aircraft types) or more if the approach charts require a higher value for obstacle consideration. 4.3. Conclusion Landing weight must satisfy the structural constraints. So, the first limitation is: LW ≤ maximum structural landing weight Landing weight is limited by aircraft performance (runway limitation and go- around limitation). Thus, the second condition is: 123 LANDING Getting to Grips with Aircraft Performance LW ≤ maximum performance landing weight Therefore, from these two conditions, it is possible to deduce the expression of the maximum allowed landing weight called maximum regulatory landing weight (MLW): maximum structural landing weight    MLW = minimum  maximum landing weight limited by performance    5. IN-FLIGHT REQUIREMENTS 5.1. In-Flight Failure JAR-OPS 1.400 Subpart D FAR 25.473 Subpart C “JAR-OPS 1.400 Before commencing an approach to land, the commander must satisfy himself that, according to the information available to him, the weather at the aerodrome and the condition of the runway intended to be used should not prevent a safe approach, landing or missed approach, having regard to the performance information contained in the Operations Manual. The in-flight determination of the landing distance should be based on the latest available report, preferably not more than 30 minutes before the expected landing time.” In the event of an aircraft system failure occurring in flight, and affecting landing performance, the runway length to be considered for landing is the actual landing distance without failure multiplied by the landing distance coefficient associated to the failure. These coefficients, as well as the ALDs for each runway state, are published in Airbus’ operational documentation (Flight Crew Operating Manual and Quick Reference Handbook). Note that the required landing distance concept no longer applies and the margins retained for alternate airport selection are at the captain’s discretion. 5.2. Overweight Landing Requirements In exceptional conditions (in-flight turn-back or diversion), an immediate landing at a weight above the Maximum Landing weight is permitted, provided pilots follow the abnormal overweight procedure. 124 Getting to Grips with Aircraft Performance LANDING JAR 25.473 Subpart C FAR 25.473 Subpart C The aircraft’s structural resistance is protected for a landing at the Maximum structural Takeoff Weight (MTOW), with a rate of descent of -360 feet per minute. Nevertheless, the minimum required air climb gradients, in the case of a go- around, must be complied with. For certain aircraft types, the go-around can be performed in CONF 1+F if the climb gradient cannot be achieved in CONF 2. The landing configuration is then CONF 3. That’s possible when VS1g (CONF 1+F) < 110% VS1g (CONF 3). 5.3. Fuel Jettisoning Conditions JAR 25.1001 Subpart A FAR 25.1001 Subpart E “JAR/FAR 25.1001 A fuel jettisoning system must be installed on each aeroplane unless it is shown that the aeroplane meets the climb requirements of Approach Climb gradient and Landing Climb gradient at maximum take-off weight, less the actual or computed weight of fuel necessary for a 15-minute flight comprised of a take-off, go-around, and landing at the airport of departure with the aeroplane configuration, speed, power, and thrust the same as that used in meeting the applicable take-off, approach, and landing climb performance requirements of this JAR-25.” When the Maximum Takeoff Weight (MTOW), less the weight of fuel necessary for a 15-minute flight (including takeoff, approach, and landing at the departure airport) is more than the maximum go-around weight, a fuel jettisoning system must be available. The aircraft must comply with go-around requirements 15-min emergency flight MTOW Figure E9: Fuel Jettisoning 125