P1: NAI/NAI/SPH P2: NAI JWBK JWBK169-Swatton June 13, :13 Printer: Yet to come. Part 2 Scheduled Performance Theory

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1 Part 2 Scheduled Performance Theory 119

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3 6 Performance Planning 6.1 Regulations and Requirements Performance regulations and requirements are a set of flight safety rules established to ensure that any aeroplane engaged on a public transport flight is despatched at a mass which, with the known and forecast conditions, the pilot is held to be unlikely to have to make critical performance decisions in flight, at times when he/she is likely to be under pressure. The foundation of all performance requirements is a scale of probabilities that is based on the statistics and analysis of past aircraft accidents and incidents. Flying is now ten times safer than it was in 1955 and the probability of a catastrophic accident on a public transport flight now is not significantly greater than the risk of being killed in a private motor car. This probability is about one in one million per hour of flight. Table 6.1 is a summary of the scale of probabilities used for determining performance requirements by the EASA and is shown in CS 25 Book 2, p. 2-F-43. It gives brief descriptions and examples for each major group. AMC Scheduled Performance The primary objective of scheduled or planned performance is the determination of the maximum TOM that will ensure the successful attainment of the predetermined safety level in all phases of flight. The CAA was entrusted with the responsibility of ensuring that all British registered public transport aeroplanes attain an adequate minimum safety standard irrespective of the size of the aeroplane, its number of engines or the phase of flight. The Remote probability of 10 6 was selected as the target for all public transport aircraft scheduled performance and has now been adopted by the EASA as that for all European registered public transport aeroplanes and is the one that should be learnt from Table 6.1 for the examination. To discharge its commission the CAA introduced three measures: 1. All public transport aeroplanes were divided into groups in which each type of aeroplane has approximately the same performance capabilities. 2. Legislation was devised for each phase of flight, both high and low performance aeroplanes that would produce approximately the same level of safety for all groups of aeroplanes. 3. The performance safety level to be used for all calculations was specified, together with the way in which that level has to be determined. Aircraft Performance Theory and Practice for Pilots C 2008 John Wiley & Sons, Ltd P. J. Swatton 121

4 122 PERFORMANCE PLANNING Table 6.1 The scale of probabilities. Classification of CS 25 Effect on aircraft failure conditions Probability and occupants Examples Minor Frequent probable Normal Heavy landing Likely to occur during the life of each aircraft Minor Reasonably probable Operating limitations Engine failure Unlikely to occur often during the life of each aeroplane. Major Unlikely to occur to each aeroplane during its life, but may occur several times during the life of a number of aircraft of the type. Hazardous Possible, but unlikely to occur in the total life of a number of aircraft of the same type Remote improbable 10 7 Extremely remote improbable 10 9 Catastrophic Extremely Remote Improbable emergency procedures Significant reduction in safety margins. Difficult for crew to cope. Large reductions in safety margins. Crew extended because of workload. Serious or fatal injuries to a small number of passengers. Aeroplane destroyed. Multiple deaths Low-speed overrun. Falling below the take-off net flight path. Minor damage. Possible passenger injuries. High-speed overrun. Ditching. Extensive damage. Possible loss of life. Hitting obstacle in the take-off net flight path. Double engine failure on a twin. Mid-air collision. Hitting terrain on approach to land. Similar measures were introduced by the JAA in 1998 dividing all public transport aeroplanes into Classes which were subsequently adopted by EASA using JAR-OPS, CS 25 and CS 23 as the legislative documents. 6.2 The Performance Class System For the purposes of scheduled performance regulations and requirements all public transport passengercarrying aeroplanes are divided into Classes: Class A Aeroplanes This Class has the most stringent requirements of all classes and is used for all multi-engined turbopropeller aeroplanes having ten or more passenger seats or a maximum take-off mass exceeding 5700 kg and all multi-engined turbo-jet aeroplanes. Aircraft in this Class can sustain an engine failure in any

5 PERFORMANCE LEGISLATION 123 phase of flight between the commencement of the take-off run and the end of the landing run without diminishing the safety below an acceptable level. A forced landing should not be necessary because of performance considerations. Class A aeroplanes are permitted to operate on contaminated runways. They are allowed to operate with certain configuration deviations without endangering the safety of the aeroplane. These requirements ensure compliance with the standards promulgated in paragraph 2.2 of Part III of ICAO Annex 8 for transport aeroplanes and those of CS 25. The performance data are published in the Aeroplane Flight Manual. Examples in this Class are: DC10, B707, B727, B737, B747, B767, and B777. JAR-OPS 1.470(a) Class B Aeroplanes This Class includes all propeller driven aeroplanes having nine or less passenger seats and a maximum TOM of 5700 kg or less. Any twin-engined aeroplane in this Class that cannot attain the minimum climb standards specified in Appendix 1 to JAR-OPS 1.525(b) shall be treated as a single-engined aeroplane. Performance accountability for engine failure on a multi-engined aircraft need not be considered below a height of 300 ft. IEM OPS paragraph 1. The performance requirements for this class of aeroplanes are those of CS23. Single-engined aeroplanes are prohibited from operating at night or in IMC (except under Special VFR) and are restricted to routes and areas in which surfaces are available to permit a safe forced landing to be executed. JAR-OPS 1.470(b) and 525(a) Class C Aeroplanes This Class includes all reciprocating-engined aeroplanes with ten or more passenger seats or a maximum TOM exceeding 5700 kg. Aircraft included in this Class are able to operate on contaminated surfaces and are able to suffer an engine failure in any phase of flight without endangering the aeroplane. JAR-OPS 1.470(c) Unclassified Aeroplanes that have specialized design features that affect the performance in such a manner that it is impossible to fully comply with the requirements of the appropriate Class of aeroplanes are considered Unclassified (e.g. Seaplanes, Supersonic aeroplanes). Specialized performance requirements applied to these aircraft ensure an equivalent level of safety is attained as though the aeroplane had been included in the relevant Class. JAR-OPS 1.470(d). The manner in which a particular aircraft type is to be flown, the purpose for which it may be used and the absolute maximum TOM are specified in the Flight and Operating Data Manuals. These are issued as part of the Certificate of Airworthiness. 6.3 Performance Legislation The minimum performance standards deemed acceptable by EASA for each Class of aeroplanes and for each phase of flight are published in the appropriate airworthiness requirements manual. Because of the wide disparity of the safety standards between performance classes it was necessary to introduce two complementary measures which when imposed together produce a uniform safety standard for all public transport aeroplanes, irrespective of the performance class. They were: 1. Operating Regulations that were introduced on 1April 1998 in JAR-OPS. 2. Airworthiness Requirements, which are the minimum acceptable performance levels in all phases of flight, are detailed in CS 25 and CS 23.

6 124 PERFORMANCE PLANNING Operational Regulations The operational regulations applicable to UK registered aeroplanes regarding the mass and performance used for public transport are legally permitted by ANO Article 30 and prescribed in AN(G)R s. They are legally enforceable by virtue of Statutory Instruments No. 2005/1970 The regulations in JAR-OPS will supersede them when an appropriate statute is approved by Parliament. For each performance class contained in this document there is a set of despatch rules, which is aimed at producing a maximum TOM, using the forecast conditions for take-off, route, destination aerodrome and alternate aerodrome. To obtain an approximately uniform level of safety for all public transport flights these have the least stringent operational regulations for the performance class that has the most stringent airworthiness requirements and vice versa. The application of these rules ensures that the aircraft performance characteristics as scheduled in the Flight Manual are properly matched to the route and climatic conditions Airworthiness Requirements The law governing the operation of public transport aeroplanes in the UK is contained in the Air Navigation Order (ANO) and requires all aeroplanes to be registered (Article 3) and to have a valid Certificate of Airworthiness (Article 7). All public transport aircraft on the UK register are certificated according to the appropriate airworthiness code of a particular performance class. See Table 6.2. Table 6.2 Applicable paragraphs in regulatory documents. Performance class A B C Document CS25 JAR OPS1 CS23 JAR OPS1 JAR OPS1 Take-off (a) Climb limit (a) (a) 565(a) (b) Field-length limit 109/ (b) (b) 565(b) (c) Flight path One-engine inoperative 111/ En-route All engines operating Inoperative power units (a) One engine 123(b) (b) Two engines 123(c) Landing (a) Approach climb limit 121(d) 510(a) (b) Field-length (dry) (c) Field-length (wet) (d) Landing climb limit (b)

7 PERFORMANCE PLANNING 125 JAR-OPS, Certification Standards Document 25 (CS 25) and Certification Standards Document 23 (CS 23) are the current regulatory documents for the operation of public transport aeroplanes and are discussed in detail in this book. They are mandatory for all passenger-carrying aeroplanes requiring registration in the UK or any other European country. 6.4 Aeroplane Performance Levels Measured Performance The performance actually achieved in both high and low performance conditions are measured by the manufacturers. After sufficient measurements have been recorded, the makers produce a set of measured performance figures. These are the average performance figures of an aircraft or group of aircraft, having been tested by the required method under specified conditions. However, they are unrealistic because they are measurements of a brand new aeroplane being flown by a highly skilled test pilot. So they have to be adjusted by the engine fleet mean performance or the minimum acceptance power or thrust to obtain the aircraft s gross or average performance Gross Performance All aeroplanes of the same type perform slightly differently, even when flown by the same pilot in exactly the same conditions and in accordance with the techniques prescribed in the Flight Manual. Gross performance therefore represents the average performance that a fleet of aircraft can be expected to achieve if they are satisfactorily maintained. There is at least a 50 % probability of the gross performance level being exceeded by the actual performance of any aircraft of the specified type, measured at any time. In other words, it is the level of performance that an average pilot flying an average aeroplane could be reasonably expected to attain Net Performance To account for further variations in performance caused by manoeuvring, piloting technique and temporary below average performance, the gross performance values are further diminished for each phase of flight, as specified by the EASA in the CS documents. This is the safety factorization. The resulting net performance figures are those used in the Flight Manual and Operating Data Manual. Where the gross performance is the average in a normal distribution, the net performance corresponds to approximately five standard deviations. It is based on an incident probability rate of one in one million flights, making it a remote probability, that the aircraft will not achieve the specified performance level. 6.5 Performance Planning The prime objective of the EASA adopting JAR-OPS, CS25 and CS23 is safety. These regulations ensure that the aircraft is constructed and operated in the safest manner possible and that all aircraft operators are legally obliged to fly within the limitations imposed by these rules and regulations. To operate within these boundaries the aircraft must be able to manoeuvre safely, even after the critical engine fails at the most crucial point in flight. Thus space is of paramount importance. The space required to manoeuvre must never exceed the space available. Sound performance planning ensures that this goal is achieved. Time and fuel used in manoeuvring are relatively unimportant; but operators must be concerned that the maximum profitability is achieved by carrying the maximum traffic load.

8 126 PERFORMANCE PLANNING Essential Data To enable the performance calculations to be made and comply with the regulations of JAR-OPS 1, information is required from two sources: 1. Aerodrome: The various distances, runway slopes, obstructions and elevations required for the performance calculations are extracted from the Aeronautical Information Publication (AIP), and from the ICAO Aeronautical Chart catalogue. 2. Meteorological: The temperature used at aerodrome level may be measured or forecast. However, the altitude used in all performance calculations is the pressure altitude, which is the reading of an altimeter with hpa set on the sub-scale. This altitude is not often available and the QFE or QNH has to be used to convert the airfield elevation to a pressure altitude. The wind component relative to the appropriate runway may be measured or forecast The International Standard Atmosphere The basis for all performance calculations is the International Standard Atmosphere (ISA) which is defined as a perfect dry gas, having a mean sea level temperature of +15 C, which decreases at the rate of 1.98 C for every 1000 ft increase of altitude up the tropopause which is at an altitude of ft above which the temperature is assumed to remain constant at 56.5 C. The mean sea level (MSL) atmospheric pressure is assumed hpa (29.92 in. Hg). See Table ISA Deviation It is essential to present performance data at temperatures other than the ISA temperature for all flight levels within the performance spectrum envelope. If this were to be attempted for the actual or forecast temperatures, it would usually be impractible and in some instances impossible. To overcome the presentation difficulty and retain the coverage or range required, it is necessary to use ISA deviation. This is simply the algebraic difference between the actual (or forecast) temperature and the ISA temperature for the flight level under consideration. It is calculated by subtracting the ISA temperature from the Actual (or forecast) temperature for that particular altitude. In other words: ISA Deviation = Ambient temperature Standard Temperature Usually 5 C bands of temperature deviation are used for data presentation in flight manuals to reduce the size of the document or to prevent any graph becoming overcrowded and unreadable JSA Deviation As an alternative to ISA deviation some aircraft manuals use the Jet Standard Atmosphere (JSA) Deviation which assumes a temperature lapse rate of 2 /1000 ft and that the atmosphere has no tropopause, the temperature is, therefore, assumed to continue decreasing at this rate beyond ft Height and Altitude Three parameters are used for vertical referencing of position in aviation. They are the airfield surface level, mean sea level (MSL) and the standard pressure level of hpa. It would be convenient if the performance data could be related to the aerodrome elevation because this is fixed and published in the Aeronautical Information Publication. This is impractical because of the vast range that would have to be covered. Mean sea level and pressure altitude are the only permissible references for assessing altitude for the purposes of aircraft performance calculations, provided that the one selected by the manufacturers for the Flight Manual is used consistently throughout the manual. Alternatively, any combination of them may be used in a conservative manner.

9 PERFORMANCE PLANNING 127 Table 6.3 International Standard Atmosphere (Dry Air). Pressure Temperature Density Height Thickness of 1 hpa layer hpa C F gm 3 m ft m ft Using MSL avoids the problem of the range of heights and would be ideal from a safety viewpoint; but again this would be too variable because of the temperature and pressure range that would be required. The only practical datum to which aircraft performance can be related is the standard pressure level of hpa Pressure Altitude In Aeroplane Flight Manuals (AFMs) the word altitude refers strictly to pressure altitude, which can be defined as the vertical distance from the hpa pressure level. Therefore, aerodrome and obstacle elevations must be converted to pressure altitude before they can be used in performance graphs. Many large aerodromes provide the aerodrome pressure altitude as part of their hourly weather reports. To correct an aerodrome elevation to become a pressure altitude if Table 6.4 is not available use the following formulae: A/F Pressure Altitude = Aerodrome elevation in ft + [( hpa QNH) 27 ft] A/F pressure Altitude = ( hpa QFE) 27 ft To correct an altitude for the temperature errors of the altimeter use the following formula: Altitude Correction = 4 ISA Deviation Indicated Altitude 1000 ft

10 128 PERFORMANCE PLANNING Table 6.4 ISA height in feet above the standard pressure level.* Pressure (hpa) Enter with QFE to read Aerodrome Pressure Altitude. Enter with QNH to read the correction to apply to Aerodrome/Obstacle Pressure Altitude.

11 ALTIMETER CORRECTIONS Density Altitude The performance data for small piston/propeller-driven aeroplanes is calculated using density altitude, which is pressure altitude corrected for non-standard temperature. It is the altitude in the standard atmosphere at which the prevailing density occurs and can be calculated by using the formula: Density Altitude = Pressure Altitude + (118.8 ISA Deviation) 6.6 Altimeter Corrections The construction of the altimeter is such that it will only indicate the true height above mean sea level if the actual conditions of temperature, pressure and lapse rate are precisely the same as the International Standard Atmosphere values for these factors. Rarely do these circumstances occur and an error is introduced to the indications that can be directly attributed to the deviation from the ISA conditions. The magnitude of any such error, in particular barometric and temperature, is related to the size of the deviation. Although they can be calculated, neither can be compensated for in the instrument. Other errors inherent in the construction of the instrument and the nature of its operation can be calibrated, listed on a correction card and due allowance made for them. Because Scheduled Performance calculations are concerned with ensuring that the aircraft obtains adequate vertical separation from all obstacles encountered during any particular flight, it is important that the two errors that cannot be calibrated and are caused by non-standard atmospheric conditions be properly understood to ensure adequate allowance is made for them. Obstacle heights are TRUE heights above MSL. To enable an accurate clearance height over any obstacle to be determined, it is essential that the aeroplane s indicated altitude be corrected for all errors to obtain the TRUE altitude of the aeroplane. This is particularly important for the period of flight during the initial climb directly after take-off, when for Class A aeroplanes the minimum net obstacle clearance legally required is only 35 ft in straight flight or 50 ft during a turn. For Class B aeroplanes the required clearance in straight flight is 50 ft. It is also important during the approach to land when the obstacle clearance limit may be as low as 200 ft above the surface level Barometric Error Barometric error is caused when the MSL pressure differs from the ISA value of hpa. Offsetting the datum from which the altitmeter measures the aircraft s height to the value of the actual MSL pressure can compensate for this error. This is done by means of a setting knob that is directly linked to a sub-scale. It enables the measuring datum to be set to any desired value. This error is of particular significance in mountainous areas if an aeroplane is flying at safety altitude, or is compelled to descend to safety altitude when the local MSL pressure may not be known and the sub-scale has to be set to the forecast value. If the MSL pressure is unknown at take-off the sub-scale can be adjusted so that the instrument indicates the aerodrome elevation plus the height of the altimeter above the aerodrome surface. This method ensures that the indicated altitude is only subject to temperature error plus the calibrated instrument error for this phase of flight. If the altimeter sub-scale is not reset during flight to the local MSL pressure the altimeter of an aircraft flying from a high-pressure area to a low-pressure area will over read by an amount in feet approximately equal to the pressure difference multiplied by 27. i.e. from High to Low indication High. This could be dangerous. When flying from a low-pressure area to a high-pressure area the altimeter will under read. i.e. from Low to High indication Low Temperature Error Because of the close relationship between temperature and pressure, any deviation between the surface temperature and the ISA assumed value of +15 C is compensated when the sub-scale is set to the local

12 130 PERFORMANCE PLANNING MSL pressure value. However, this correction does not compensate for any lapse rate difference from that of ISA. The error caused by a differing lapse rate is temperature error. Cold air is denser than warm air and therefore has a greater lapse rate. This causes the pressure at any given level above the surface to be lower than it would be at the same level in warm air. Because the lapse rate in cold air is greater, the altimeter over-reads, falsely indicating the aeroplane to be higher than it really is. When the actual air temperature is below that of ISA, the error is particularly dangerous if no allowance is made for it when estimating obstacle clearance, because the actual vertical separation will less than that indicated. An investigation made in 1979 confirmed that an allowance of 4 ft per 1000 ft of indicated altitude must be made for every 1 C difference of the actual temperature from that of ISA at that altitude. If the static air temperature is lower than the ISA temperature, the correction must be subtracted from the indicated altitude to obtain the true altitude above the datum set on the altimeter sub-scale. It is estimated that the error caused if the temperature error is not corrected can be as high as 9.44 % of the indicated altitude in temperate climates, but in extreme low temperature conditions it can be as much as 25 %. If the indicated altitude is corrected it will be within 1.5 % of the true altitude in normal temperature conditions and within 3 % in extreme temperature conditions. The formula to be used to correct for temperature error is: 1. Altitude Correction = 4 ISA Deviation Indicated Altitude Temperature below ISA then: True Altitude = (Indicated Altitude Correction) 3. Temperature above ISA then: True Altitude = (Indicated Altitude + Correction) Temperature Considerations The temperature of the air quoted for the aerodrome surface is measured by a thermometer hung in a louvered screen 4 ft above the ground, which shields it from the direct rays of the sun. Thus it is not a true measurement of the temperature at the runway threshold, which is exposed to the sun and re-radiates heat. The difference between these two temperatures is not significant in temperate and cold climates, but in tropical and sub-tropical climates, it can make a considerable difference to the take-off and landing performance of an aircraft. In these circumstances, the performance calculations are too optimistic because the reported temperature is too low. In practice, some airlines advise their aircrew that when operating in hot climates in daylight hours it is prudent to increase the reported surface temperature by 2 C before using it in performance computations. 6.7 Flight Manuals The Flight Manual is a legal document and forms an integral part of the Certificate of Airworthiness (ANO Arts 7 and 8). It contains the information essential, from a Scheduled Performance viewpoint, to the safe operation of the aircraft. Absolute limiting values quoted in the Manual are therefore legally enforceable, and can only be exceeded for a particular flight if specific permission is obtained from the Authority before the flight begins. If any particular limitation is exceeded, the aircraft s Scheduled Performance guarantee is automatically invalidated. The conditions observed in the construction of all graphical data and the range of data which must be included is specified in JAR-OPS and in the UK in AN(G)R. The minimum amount of information provided in any particular Aeroplane Flight Manual must be sufficient to enable it to be operated in at least one region of the world in which the prevailing meteorological conditions would only infrequently be outside the range provided. Manufacturers usually determine and schedule sufficient data to enable the aircraft to be safely operated anywhere in the world. On the rare occasions when the prevailing conditions fall outside the

13 FLIGHT MANUALS 131 range covered by the Flight Manual, any information required must not be extrapolated from the graphs, unless specifically permitted. The manufacturer is compelled to include data in the Flight Manual, which allows for the effect of any equipment or configuration peculiar to that specific aeroplane type which if used or if unserviceable, would have a significant effect on its performance. For example using the anti-icing system, the watermethanol injection or not being able to use the reverse thrust or anti-skid system Validity of Information All flight manuals include a statement regarding the validity of the performance information contained within. The data scheduled cannot be considered valid unless this statement includes the following mandatory clauses: 1. The performance Class in which the aeroplane is classified. 2. Extrapolation of performance information is only valid if specifically permitted and within the limitations stated. 3. Performance data for any temperature beyond the maximum of the range scheduled are not valid. 4. The appropriate climb-limited mass for take-off or landing is the maximum for that phase of flight. If it is exceeded, the related performance data are automatically invalidated. 5. The maximum altitude at which an attempt to relight or restart an inoperative power unit is clearly stated. 6. A representative TAS is given that is to be used for calculating any route limitation and is often termed the Over Water Speed. 7. Equipment limitations. The aeroplane manufacturers are legally required to include in the aircraft Flight Manual the following details of equipment or configuration that will affect the scheduled performance: (a) a list defining the certificated flap settings for the aeroplane type and the way in which performance data are used if flap is selected; (b) the effect on performance data of operating specific equipment; (c) the effect on performance data of the unserviceability of specific equipments. Some of these legal requirements may be contained in a Configuration Deviation List (CDL) or Minimum Equipment List (MEL). From this list, it will be seen that the air conditioning system (ACS), reversethrust, anti-skid and power management computer (PMC) are considered to have a significant effect on the aircraft performance. A statement is included specifying the allowance that must be made for each type of equipment should it be inoperative or unserviceable Specific Conditions and Associated Ranges Aerodrome Altitude Although the requirements specify that aerodrome altitudes must be scheduled from 1000 ft below MSL to 2000 ft above MSL, it is usual for manufacturers to present a range from 1000 ft below MSL to ft above MSL. The aerodrome altitude is normally presented as a pressure altitude Cruising Altitude The data range required for the en-route phase of flight is from MSL to the maximum pressure altitude at which the aeroplane is able to operate having regard to the AUM and to the ambient temperature.

14 132 PERFORMANCE PLANNING Temperature The range of temperatures required for all performance data is from ISA +15 C to ISA 15 C. However, most manufacturers provide data up to a maximum temperature of ISA +30 C Wind Aircraft manufacturers are only obliged to provide take-off and landing performance data for a range of wind speeds from 15 kt head component to 5 kt tail component. If these limitations were observed, they would unnecessarily penalize the operator; so most flight manuals are produced with a wind component range from 40 kt head to 10 kt tail. Before these wind components are used in take-off and landing calculations AN(G)R s, JAR-OPS and CS (d)(1) require that all headwind components be reduced by 50 % and all tailwind components are increased by 50 %. The safety factorization imposed is usually already incorporated in the scheduled data of the wind grids in the various graphs by changing the slope of the grid-lines or by varying the scale of the grid so that the actual (or forecast) wind component can be used directly on the wind grid without alteration. The effect of the safety factorization is diminished in direct proportion to the size of across track angle. The greatest diminishment occurs when the wind direction is at 90 to the runway. If the wind is gusting over a range of speeds, the component that must be used in all performance calculations is the most unfavourable one. Crosswind effect is not normally scheduled. If, however, the EASA decides that within the maximum crosswind limitation the effect is significant above a particular speed for a specific type of aeroplane, then the performance data for that aeroplane type must account for this. The AFM will contain a statement to this effect if such is the case Runway Slope For the purposes of take-off and landing performance calculations, runway slope is assumed to be uniform over the entire length of the runway. If the slope varies along the runway length then the average slope is that which is promulgated and used with all field-lengths for take-off performance calculations. The range of slopes that must be included in Class A AFMs for take-off calculations is from +2%to 2% and the effective runway gradient is to be used for take-off computations. CS (d)(2). For Class A aeroplane landing performance calculations, the average slope of the runway must be used if it exceeds ±2 %. Although an operator does not legally have to use the runway slope for lesser values, it may be used if so desired provided there is a means of calculating its effect. If there were a means available in the AFM of allowing for runway slopes of less than 2 % then a prudent operator would account for any runway downslope in the landing calculations particularly with in-flight landing performance calculations, when approaching or overhead the landing aerodrome. JAR-OPS The formula for calculating runway slope is: Runway Slope % = Change of height in feet/runway length in feet Performance Calculations and Limitations Performance Calculations There are four phases of flight that are take-off, take-off climb, cruise and landing. For each phase of flight, there is a set of operating regulations in JAR-OPS and a set of minimum acceptable performance criteria specified in either CS 25 or CS 23 as appropriate. The data provided in the AFM by the manufacturers are based on the assumption that the aeroplane is fully serviceable and is operated in accordance with the recommended techniques and power settings.

15 PERFORMANCE CALCULATIONS AND LIMITATIONS 133 It is further assumed that it is being operated on a hard, dry, level runway having a co-efficient of friction of 0.5 or greater, in still air. If any of these assumptions are incorrect, due allowance must be made for them in the performance computations. Usually all take-off and landing graphs include grids that apply the effect of runway slope, wind component and either grids or statements in words to apply the effect of the use of the air conditioning system (ACS) and the anti-icing system or the non-use of the power management computer (PMC). Separate graphs are normally provided to account any other irregularity such as a very slippery runway surface; reverse thrust inoperative and high lift devices inoperative. If these abnormalities are present at take-off then the accelerate/stop distance required (ASDR) is increased; only the unserviceability of high lift devices will increase the take-off distance required (TODR). If the pilot uses a rolling technique to line-up and start the take-off while applying power, instead of a stationary start and applying full take-off power against the brakes, then all the take-off calculations will be invalidated. This is because some of the available distance is used to line-up and is during the period that the engines are spooling up to maximum take-off power and the calculations assume full take-off power over the whole distance available. When the correct technique is used the maximum take-off power for a jet engined aeroplane or the maximum efficiency of the propellers for propeller driven aeroplanes is achieved between 40 kt and 80 kt during the take-off ground run. Initially the thrust for both types of engine will decrease but will recover and then increase as the aeroplane accelerates Distances There are three types of distance in performance calculations, the first two are qualified by a suffix and the third has no qualification: Available Available distances are those that are published in the AIP and are fixed such as take-off run available (TORA), accelerate/stop distance available (ASDA) and take-off distance available (TODA). They are unaffected by any condition, except a temporary obstruction that may cause them to be reduced in length and this would be notified by NOTAM Required Required distances are those calculated from the Flight Manual graphs when all of the conditions are applied either manually or by using the graphs, including the safety factorization, such as take-off run required (TORR), accelerate/stop distance required (ASDR) and take-off distance required (TODR). They are, therefore, net distances. In CAP 698 the MRJT graphs are already factorized for safety Unqualified An unqualified distance has no descriptive suffix for example take-off run (TOR), accelerate/stop distance (ASD) and take-off distance (TOD). They are the distances derived from the graphs factorized for surface slope, type and condition but without the safety factorization. In other words, they are the distances the aeroplane would actually use in the prevailing conditions. These distances are gross distances Limitations The Certificate of Airworthiness issued for a particular aircraft type states the manner in which the aircraft must be flown and the purpose for which it may be used. The mass limitations stated therein are absolute if the maker s guarantee of performance and handling is to remain valid. Under exceptional circumstances

16 134 PERFORMANCE PLANNING the manufacturers and the EASA may together grant permission to exceed a particular limiting mass in which case the stated performance will almost certainly not be attained. All Classes of public transport aeroplanes are subject to the following restrictions Structural Limitations The maximum permitted masses for take-off, for landing and for the aeroplane without usable fuel (the zero fuel mass) are all absolute values that are specified in the AFM. If any one of these limitations is ignored it could have disastrous consequences. If it is permissible to exceed the maximum normal take-off mass, a maximum overload mass will be quoted in the AFM. There is no guaranteed performance for this mass, and if this mass is exceeded there is a real danger of structural failure. Only the maximum landing mass may be exceeded without obtaining prior permission, and then only in an emergency Overloading Effects The effects of overloading include: 1. reduced acceleration and increased speeds for take-off 2. increased take-off ground run and take-off distance 3. decreased gradient of climb and decreased rate of climb 4. increased difficulty in clearing obstacles by the statutory minimum vertical interval 5. excessive undercarriage load, especially when using natural surface runways 6. reduced ceiling and range 7. impaired manoeuvrability and controllability 8. increased stalling speed 9. increased landing speed, requiring a longer ground run and landing distance 10. decreased brake effectiveness, especially on low coefficient of friction runways 11. reduced structural strength margins 12. inability to climb or maintain height after engine failure for multi-engined aircraft 13. possibility of exceeding the brake energy and/or tyre speed limitation CG Envelope The centre of gravity (CG) is that point on the longitudinal axis through which all of the aircraft mass acts vertically downward. The CG must remain within the safe limits specified by the manufacturers. The area between the safe forward limit and safe aft limit is the CG envelope. The position of the CG for take-off is affected by the location of the load and the fuel distribution. In flight, fuel is used and the CG will move, its position can be manipulated by using the fuel from various tanks in a particular sequence or by transferring fuel between tanks. (a) Aft CG Position To assist rotation on take-off it usual to position the CG towards the aft limit of the envelope. During flight, the fuel should be managed, if possible, to maintain the CG just forward of the aft limit of the envelope. This is often referred to as flying the flat aeroplane because trim drag is minimized. If such is the case, the fuel flow is reduced, the range is increased and the stalling speed is decreased. If, in these circumstances, the power setting remains unchanged the IAS and TAS will increase and the maximum range will increase. However, if the requirement is to increase the endurance the IAS should be kept constant and the power reduced, this will further reduce the fuel flow.

17 PERFORMANCE CALCULATIONS AND LIMITATIONS 135 If the CG position is aft of the aft limit of the CG envelope it will result in: 1. premature rotation on take-off 2. inadvertent stall in the climb 3. trimming difficulties, especially at high power settings 4. longitudinal instability, particularly in turbulence 5. degraded stall qualities. (b) Forward CG Position To enhance the approach and landing of an aeroplane the CG should be moved towards the forward limit. The CG movement should be sufficient to enhance control on touchdown but not to significantly increase the stalling speed. If the CG position is forward of the forward limit of the CG envelope it will result in: 1. difficulty in rotating at take-off 2. increased stalling speed 3. greater induced drag, which will increase the fuel consumption and reduce range 4. insufficient nose-up trim available during approach to land, making a stable approach more difficult Crosswind Limitation For take-off with a crosswind, the displacement of the aircraft control surfaces, to maintain the runway track during the take-off ground run, increases the total drag and reduces the acceleration up to VLOF on some aeroplanes. The size of the fin and rudder and the length of the fuselage determine the magnitude of the counteracting moment that can be generated to overcome the tendency of the aeroplane to weathercock into a crosswind. This determines the maximum crosswind component that can be adequately counteracted by the controls and is specified in the AFM. The maximum safe crosswind limit, for take-off and landing, for Class A aeroplanes is valid for both non-icing and icing conditions, is 20 kt or 0.2 VSR whichever is greater, except that it need not exceed 25 kt. In the UK it is a legal requirement that an aerodrome should have sufficient runways (marked as such), to ensure that on not less than 97 % of occasions there is at least one direction of take-off and landing available with a crosswind acceptable for the types of aeroplane likely to use the aerodrome. This usually means that the maximum crosswind experienced at most major aerodromes is 20 kt. If the physical geography does not allow the main runway to be constructed into the prevailing wind, the licensing authority may reduce the maximum permissible crosswind limitation. The safety factorization imposed by JAR-OPS on the use of the along track wind component, i.e. 50 % of a headwind and 150 % of a tailwind, increasingly loses its effectiveness with an increasing crosswind component until there is no safety element when the wind is exactly 90 to the runway Brake-Energy Limitation The energy absorption capability of the aircraft braking system has a design limitation, usually a maximum operating temperature between 450 C and 500 C, beyond which it will fail to stop the aeroplane. The ability of the braking system to stop the aeroplane decreases with an increase of altitude, and/or temperature tailwind and /or downhill slope, so the design limitation is reached sooner. This limitation is normally related to the aircraft s speed and is referred to as VMBE. Decision speed, V1 must never exceed VMBE. If it does, the TOM must be reduced until V1 = VMBE. If the aircraft has a prolonged taxiing period and there is insufficient time for the brakes to cool before commencing the take-off ground run the brake temperatures will already be high. This will reduce their energy absorption capacity, and is a factor that cannot be scheduled but must be accounted.

18 136 PERFORMANCE PLANNING Tyre Speed Limitation The increased masses and speeds of modern transport aircraft cause the tyre temperatures during the take-off ground run and landing ground run to become very high. All tyres are fitted with fusible plugs, which melt at a predetermined temperature to give protection against overpressure due to high wheel temperatures caused by excessive periods of braking (see Chapter 18). All tyres have a maximum groundspeed specified in the AFM. A graph for the appropriate type of tyre is provided in the AFM. It combines the entries of aerodrome pressure altitude, air temperature and along track wind component to facilitate the determination of the tyre-speed limited TOM for the prevailing conditions. If the calculated tyre-speed limited TOM is less than any other limitation it becomes the limiting TOM. The most adverse conditions for the tyre speed limited TOM either individually or in any combination are high aerodrome elevation, high ambient air temperature and a tailwind component. Americans refer to the tyre limiting speed as VTIRE. Runway slope has no effect on the value of the limiting tyre speed or the tyre-speed limited TOM Practical Considerations If the actual TOM is less than the field-length-limited TOM a range of V1s is available, the lowest value is limited by the TODA or VMCG whichever produces the greatest restriction and the highest value is limited by ASDA or VR whichever causes the least restriction. Jet aeroplanes normally use the lowest value, because they have a large surplus of thrust available over thrust required. Turbo-prop aircraft that do not have that excess would use the higher value in the range. For an aerodrome with unbalanced field-lengths the V1 will be higher than the V1 for the same aerodrome if the field-lengths are artificially reduced to make them balanced. Using a V1 below the balanced field-length V1 ensures that there is ample distance in which to stop the aircraft if the takeoff has to be abandoned. However, this distance is reduced if the V1 used is higher than the balanced field-length V1. The length of the take-off distance is affected by the ability of the aeroplane to accelerate from V1 with one-engine-inoperative to reach VR, which is directly proportional to the TOM. The TOD for a balanced field length will be greater than that for a balanced-field if the V1 used is lower than the balanced-field V1 and less if the V1 used is greater. The reverse is true for the accelerate/stop distance. 6.9 Noise Abatement Procedures The procedure to be adopted after take-off to ensure the aircraft noise remains at an acceptable level to those on the ground is determined by the position of the noise sensitive area relative to the end of the TOD. The recommended procedure to be adopted if the noise sensitive area is close to the aerodrome is referred to as Noise Abatement Departure Procedure 1 (NAPD1). For those areas, some distance from the end of the TOD the procedure is called Noise Abatement Departure Procedure 2 (NAPD2). Both procedures can be divided into three segments NADP First Segment From screen height 35 ft to 800 ft above the aerodrome surface level the configuration is: 1. all engines operating at maximum take-off power/thrust 2. the flap/slats at the take-off setting 3. the undercarriage retracted 4. the climb speed at V to 20 kt.

19 NOISE ABATEMENT PROCEDURES Second Segment The earliest point at which it is permitted to reduce the power/thrust is 800 ft above the take-off surface level and is the point at which the second segment begins. From this point the aeroplane continues to climb in the same configuration and at the same speed until a height of 3000 ft above the take-off surface level is attained Third Segment The third segment commences at 3000 ft above the take-off surface level, and is where the aeroplane is accelerated, still climbing, until the en-route climb speed is attained. The flaps/slats are retracted in stages when the scheduled retraction speed is attained for each setting. The climb is continued to the cruising altitude at the en-route climbing speed (see Figure 6.1). 900 m Maintain positive rate of climb. Accelerate smoothly to en-route climb speed. Retract flaps/slats on schedule (3000 ft) 600 m 450 m (2000 ft) Climb at V to 20 kts Maintain reduced power Maintain flaps/slats in the take-off configuration 240 m (800 ft) Initiate power reduction at or above 800 ft Runway Take-off thrust V + 10 to 20 kts 2 Not to scale Figure 6.1 Noise abatement departure procedure NADP First Segment The configuration set for the first segment, from screen height 35 ft to 800 ft above the aerodrome surface level is: 1. all engines operating at maximum take-off power/thrust 2. the flap/slats at the take-off setting 3. the undercarriage retracted 4. the climb speed at V to 20 kt Second Segment At 800 ft above the take-off surface level the aeroplane is accelerated, maintaining a climbing attitude, to the minimum safe manoeuvring speed with zero flaps (VZF). The thrust is reduced during this segment, but the acceleration must continue to attain VZF +10 to 20 kt and the flaps must be retracted on schedule.

20 138 PERFORMANCE PLANNING The reduction for high by-pass ratio engines is to the normal climb thrust but for low by-pass engines the thrust must be reduced to less than the normal climb thrust but not less than that required to maintain the final segment of the one-engine-inoperative gross flight path. For aeroplanes having a slow rate of flap retraction the thrust should be reduced at an intermediate flap setting Third Segment The third segment commences at 3000 ft at which point the aeroplane is accelerated, still climbing, until the en-route climb speed is attained. The flaps/slats are retracted in stages when the scheduled retraction speed is attained for each setting. The climb is continued to the cruising altitude at the en-route climbing speed (see Figure 6.2). 900 m (3000 ft) Accelerate smoothly to en-route climb speed 600 m 450 m 240 m (2000 ft) (1500 ft) (800 ft) Not before 800 ft and whilst maintaining a positive rate of climb accelerate towards V ZF and reduce power with the initiation of the first flap/slat retraction or when flaps/slats are retracted and whilst maintaining a positive rate of climb, reduce power and climb at V ZF+ 10 to 20 knots Runway Take-off thrust V + 10 to 20 kts 2 Not to scale Figure 6.2 Noise abatement departure procedure 2.