Vereniging van Nederlandse Verkeersvliegers Dutch Air Line Pilots Association Position Paper 07 / 4 Performance Optimization Revision: 19 th September 2007 This position paper represents the opinion of the Dutch Air Line Pilots Association based on IFALPA / ECA policy, legislation, scientific research and manufacturer guidelines and recommendations.
Issue Software based takeoff performance tools together with the use of digital performance information allow for the optimisation of takeoff performance by using first principles calculation methods, optimum flap settings and optimised takeoff speeds and may result in the removal of (additional) margins present in a paper based methodology. General VNV recognizes the economic benefits resulting from the use of software based takeoff performance tools such as LINTOP or EFB based tools and the optimisation of takeoff performance. There are however several concerns which in the opinion of VNV should be addressed prior to introduction of the optimised performance in order to reduce the likelihood of potentially unsafe situations. These concerns are addressed below and concern training aspects, the availability of sufficient and clear information to the flight crew and technical considerations. Training and Standards With the introduction of optimum flap settings the flight crew will be confronted with considerably different aircraft behaviour during one of the most critical flight phases as compared to the current takeoff techniques. Notably the handling of an engine failure during takeoff identifies the need for sufficient (simulator) training and the availability of high quality background information and clear and concise instructions and regulatory background embedded in the Operations Manuals. An overview of the complexity of takeoff performance optimisation is presented in Appendix 1. Flight Crew Responsibility The flight crew is directly responsible for the safe execution of the takeoff manoeuvre. Full optimisation of takeoff performance may remove margins previously present and there are situations when full optimisation of takeoff performance may not be desirable. In order to be able to take full account of all information available prior to takeoff, such as runway state, weather, technical status of the aircraft, NOTAMS, etc. the flight crew should have a complete picture of the (performance) limitations and specifics of that particular takeoff. This is in line with the lessons learned from many takeoff accidents and incidents and identified in the FAA Takeoff Safety Training Aid and various accident and incident analyses. Key factors are knowledge of regulatory rules and certification criteria, knowledge of takeoff performance and the effects of airplane configuration and technical status as well as knowledge of available safety margins. Clearly, the presentation of takeoff speeds as function of input parameters without further information is insufficient. VNV is of the opinion that flight crews should be aware of the limitations affecting the particular takeoff by having available the weight margins with respect to the performance limitations (structural, field length, climb, obstacle, tire speed and brake energy). This has the additional advantage of contributing to the detection of possibly incorrect values. The sole option to use full rated takeoff thrust in case of doubt is a highly undesirable solution as this will not provide the required insight in available margins or limitations of that particular takeoff procedure.
Technical Considerations Data Integrity The capability to detect erroneous calculations or data corruption is clearly reduced by the calculation of point performance by a remote system. Additionally the possibility to detect errors by performing an independent check is removed. The optimisation process itself may lead to performance data (takeoff speeds and limit weights) quite different from values obtained through a (balanced) paper methodology. VNV is of the opinion that sufficiently robust measures should be in force to guarantee: Database and software integrity (NOTAMS / virus protection / firewall / encryption) Algorithm reliability (BITE / spike testing) End-user checks (e.g. actual weight versus performance limit weights, optimised takeoff speeds in relation to balanced takeoff speeds) Back-up procedures in case of system failures History has shown that there is a clear need for procedures and information to aid in the detection of erroneous takeoff performance data as outlined in a review by the Canadian Transport Safety Board (see Appendix 2). Field Performance Range of V1 Whenever the actual takeoff weight is below the field limited takeoff weight (balanced) the application of performance optimisation potentially allows a further reduction of takeoff thrust setting (increased assumed temperature or different derated thrust setting) or a variation of V 1 within the certified range or a combination thereof. Whenever the takeoff performance is not limited by field length or when the maximum allowed reduction in takeoff thrust is reached VNV would favour the adoption of a reduced V 1 policy. Clearway / Stopway Current certification standards and implementation of digital performance information allow the inclusion of clearway credit on wet runways for the engine-out case for both the 747-400 (100%) and the 777-200/300 (50%). Depending on the particular conditions this may result in the scheduling of lift-off very near the end of the runway threshold in case of an engine failure. Following concerns from IFALPA both FAA and JAA agreed this situation to be unsafe and the certification requirements were subsequently amended to deny this credit. For non-jaa certified aircraft a work-around procedure may be available by applying the slippery runway (wet/good) corrections to the dry takeoff performance, which could also result in engine-out clearway credit on wet runways. This option is not supported by VNV. Stopways usually do not have the same quality standard as the runway itself and enforcing maintenance criteria for friction levels comparable with the runway itself are often difficult to apply or are not applied at all. Certain stopways may become very slippery when wet or have a considerably reduced loading capacity when wet. It is IFALPA policy that stopways and clearways
should be considered as an additional safety margin. In any case VNV is of the opinion that the decision to include or exclude stopways or clearways in the takeoff performance calculation should be made by the flight crew. RESA Certain airfields have adopted the policy of reducing the declared Accelerate-Stop Distance Available in order to accommodate the ICAO requirements for Runway End Safety Areas (RESA). This has resulted in Takeoff Run Available (TORA) values in excess of ASDA values, which is clearly not in line with the JAA definition of a stopway. VNV/IFALPA does not support the use of RESA for inclusion in takeoff performance calculations and as such requires a thorough check of airport declared distances in order to avoid this problem. Grooved / Porous Friction Course (PFC) Performance Credit Both the 777EFB and the 737NG AFM-DPI provide for takeoff performance based on wet skidresistant surfaces. This option is based on the performance credit available in the FAR 25 Amendment 92 and JAR 25 Change 15 certification requirements for grooved or Porous Friction Course (PFC) runways and is based on accepted (conservative) performance levels of these runway surfaces equal to approximately 70% of the dry equivalent and will because of the reverse credit and reduced screen height result in roughly dry takeoff performance however with appropriate V 1 reduction and penalties for inoperative reversers. In order to stimulate the use of grooved and PFC runways IFALPA/VNV is in favour of using this option provided it is verified that the runways are indeed maintained in accordance with FAA AC 150/5320-12C or its equivalent. Typically this would mean that maintenance friction measurements satisfy the Design Objective Level (DOL) for Grooved/PFC runways and that rubber removal frequencies are sufficiently high. VNV is of the opinion that the current runway state reporting of EHAM (dry/wet) and dispatch guidelines for EHRD do not satisfy the above certification requirements and do not reflect the actual runway capability, as they are mainly based on whether or not water levels will rise above the texture depth. This is not an accepted or representative definition of dry runways but merely an indication when runway flooding will occur or when standing water will be present. Furthermore, no scientific research is available for these runways that indicates equivalent dry braking action is retained for aircraft when moisture is present on the runway. The underlying research for EHAM indicates braking action good is available, which is the equivalent of a wet runway and not of a dry runway (See VNV-VTZ Position Paper 07/1). VNV is of the opinion that performance credit in accordance with the above certification requirements (70% dry) is the only accepted method and might lead to a broader acceptance among flight crews as opposed to the dispatch rule currently applied to EHRD. In the end the takeoff performance credit would be available for all wet runway departures from EHAM and might result in an overall larger profit without compromising safety. Takeoff Obstacle Clearance Currently field performance is based either on a standard or non-standard engine failure procedure. Whenever an airport is located within high terrain with an engine failure procedure over relatively flat terrain and a SID deviation point relatively short after takeoff, fully optimised performance may prove destructive to climb out performance once the SID deviation point is passed in case of an
engine failure. This clearly shows the need for a presentation of performance margins to the flight crew and the possibility to adapt the performance parameters. JAR-OPS 1.495(f) states: An operator shall establish contingency procedures to satisfy the requirements of JAR-OPS 1.495 and to provide a safe route, avoiding obstacles, to enable the aeroplane to either comply with the enroute requirements of JAR-OPS 1.500, or land at either the aerodrome of departure or at a takeoff alternate aerodrome. Due to the absence of sufficiently accurate obstacle charts (Type B/C, which some states refuse to publish because of liability) and limited calculation resources, airlines may not always be able to fully comply with this requirement. However, with the advent of more advanced tools, the responsibility of the airline may shift towards providing more alternative routings. In any case responsibility to provide a safe routing in case of an engine failure clearly does not stop with the final takeoff segment of an engine failure procedure. NOTAM Information The presence of NOTAMs with revised obstacle heights or new obstacles is a commonality in day-today operations. With the full optimisation of takeoff performance it is therefore essential that flight crews have the ability to check whether a certain obstacle is included in the performance calculation and/or have the ability to include revised or new obstacle information in the performance calculation themselves. Other Considerations Despite the possibility of performance optimisation certain margins remain available such as the difference between gross and net performance for obstacle clearance criteria, a maximum thrust reduction of 25% relative to rated takeoff thrust and in case of use of the assumed temperature method for takeoff thrust reduction a stop margin arising from the True Airspeed (TAS) effect. By using an assumed temperature in excess of ambient air temperature, the takeoff performance is based on higher groundspeeds than those actually encountered during the takeoff and as such will lead to an additional stop margin which will become higher with increasing difference between ambient air temperature and assumed temperature. This effect can be quantified and the presentation of this additional stop margin might justify a fully optimised performance calculation.
Appendix 1: Background Information The Boeing Approach Flight Test Paper AFM BTOPS Book Building MTOPS AFM-DPI BTM Real-Time Dispatch TOPAZ MTOPS Airplane AFM-DPI BTM BTOPS MTOPS SCAP TOPAZ Airplane Flight Manual Digital Performance Information Digital Flight Manual with a graphical interface based on PC. Core calculation software is shared with operational (SCAP) software via BTM and BLM. Regulatory software program used to calculate takeoff, enroute and landing performance Boeing Takeoff Module SCAP manufacturer module used to calculate takeoff operational performance based on AFM-DPI system software. Boeing Takeoff Performance Subroutine SCAP manufacturer module used to calculate takeoff operational paper AFM-based performance. McDonnell-Douglas Takeoff Analysis Subroutine SCAP manufacturer module used to calculate takeoff operational performance from paper AFM-based databases or softwarebased databases. Standard Computerized Airplane Performance Takeoff and Landing interface specifications (as published by IATA). TakeOff Performance for AirlineZ Digital flight manual performance with a PC based menu interface. Core calculation software is shared with the operational (SCAP) software via MTOPS. Regulatory software program used to calculate takeoff performance. Source: Boeing Flight Operations Engineering Due to the possibility of reduced margins (no graphical limitations or margins), the ability to solve more complex dispatch problems and the use of updated methods, single point calculation using AFM-DPI/TOPAZ based real-time dispatch tools provides for maximum performance. This may result in increased performance limited weights or deeper reduced thrust with obvious commercial benefits. General Takeoff Performance Limitations In general takeoff performance is limited by the following requirements: Field Length Requirements with optional inclusion of clearway, stopway Climb Requirements: 1 st segment, 2 nd segment and final segment, normally limited by 2 nd segment (gear up, takeoff flap setting) climb gradient requirements Obstacle Requirements: Net Flight Path must clear all obstacles by 35 ft. The Net Flight Path is the Gross Flight Path reduced by a prescribed reduction according to FAR/JAR/CS 25 certification requirements (e.g. 0.8% for 737) Tire Speed Limit Brake Energy Limit
Range of V1 The general approach adopted by Boeing is the calculation of a Corrected Runway Length which generalizes WAT-effects (Weight-Altitude-Temperature). The corrected Engine Inoperative Takeoff Distance is the actual runway length corrected for specific conditions such as the presence and use of a clearway, the effects of runway slope, wind, anti-ice, engine bleed, MEL-items, line-up distance, etc. The corrected Engine Inoperative Accelerate-Stop Distance is the actual runway length corrected for the presence and use of a stopway, the effects of runway slope, wind, anti-ice, engine bleed, MELitems, line-up distance, etc. The actual takeoff weight determines the takeoff safety speed V 2 and the rotation speed V R is determined from V 2 as a function of altitude and temperature. Whenever field length limited the maximum performance is obtained for the balanced takeoff where the corrected Engine Inoperative Takeoff Distance is equal to the corrected Engine Inoperative Accelerate-Stop Distance, resulting in a standard V 1 /V R -ratio. When the actual takeoff weight is lower than the field length limited takeoff weight a reduced or derated takeoff thrust setting or a range of V 1 speeds or a combination of both may be available for which all legal field length requirements are satisfied, the minimum value resulting in a stop margin, the maximum value resulting in a go margin. Other requirements to be satisfied are a minimum V 1 equal to the minimum control speed V MCG and a maximum V 1 equal to the rotation speed V R in combination with tire speed and brake energy limits: Source: Boeing Flight Operations Engineering Stopway Credit ICAO Annex 14: Stopway: A defined rectangular area on the ground at the end of take-off run available prepared as a suitable area in which an aircraft can be stopped in the case of an abandoned take off. A stopway shall have the same width as the runway with which it is associated.
A stopway should be prepared or constructed so as to be capable, in the event of an abandoned take-off, of supporting the aeroplane which the stopway is intended to serve without inducing structural damage to the aeroplane. The surface of a paved stopway should be so constructed as to provide a good coefficient of friction to be compatible with that of the associated runway when the stopway is wet. Stopway credit is straightforward and can be included directly as accelerate-stop distance available (ASDA). According to JAR-OPS the accelerate-stop distance available is equal to the takeoff run available plus the length of the stopway if declared available by the appropriate authority. There have however been cases where the declared distances were not in agreement with the above definition because of the inclusion of Runway End Safety Areas (RESA). Clearway Credit ICAO Annex 14: Clearway: A defined rectangular area on the ground or water under the control of the appropriate authority selected or prepared as a suitable area over which an aeroplane may make a portion of its initial climb to a specified height. The origin of a clearway should be at the end of the take-off run available. The length of a clearway should not exceed half the length of the take-off run available. A clearway should extend laterally to a distance of at least 75 m on each side of the extended centre line of the runway. The ground in a clearway should not project above a plane having an upward slope of 1.25 per cent. Any equipment or installation required for air navigation purposes which must be located on a clearway and which would endanger an aircraft in the air shall be frangible and mounted as low as possible. Existing non-visual aids need not meet this requirement until January 1 st, 2010. Additionally in JAR/CS Definitions threshold lights may protrude above the plane if their height above the end of the runway is 0.66 m (26 inches) or less and if they are located to each side of the runway. The amount of clearway credit is expressed as the amount of the takeoff flare distance (from lift-off to the screen height) which is traversed over the clearway. Generally clearway credit is expressed as a percentage. FAA: FAR 25 Amendment 0 (effective 1 st February 1965) allows a 50% clearway credit for the flare distance between lift-off and 35 ft. This amendment does not address runway state (dry only) and typically threshold clearance may be as low as 13 feet. With the introduction of runway state accountability (dry/wet) in FAR 25 Amendment 92 (effective 20 th March 1998) it was recognized that the combination of a clearway with the 15-foot screen height for wet runways could result in a minimum height over the end of the runway of near zero (lift-off very near to the end of the runway), if clearway credit were to be permitted for wet runways in the same manner that it is currently permitted for dry runways. Both IFALPA and FAA considered this situation unacceptable. The possible presence of standing water or other types of precipitation (e.g. slush or snow) and
numerous operational factors (e.g. late or slow rotation to lift-off attitude) emphasize the need to provide more of a safety margin than would be present if lift-off were permitted so near the end of the runway. As a result clearway credit for wet runways was denied as of this amendment. JAA: Wet runway accountability was introduced in JAR 25 as early as Change 2 (effective 9 th April 1976) by requiring data to be determined to aid the selection of a V 1 for a wet runway. ACJ 25X133 required the presentation of a lowest value of V1 with adequate aerodynamic controllability, resulting in a height of 15 ft at the end of the takeoff distance and resulting in lift-off within the specified takeoff run applicable to a dry runway with clearway credit, effectively allowing full clearway credit for the engine-out case on wet runways. JAR 25 Change 5 (effective 1 st January 1979) introduced a CAA-UK national variant with a more elaborate approach to wet runway performance, allowing 100% clearway credit for the engine-out case on wet runways. With Orange Paper 25/88/1 (effective 18 th October 1988) national variants were deleted and a new paragraph 25X1591 was introduced addressing wet and contaminated runways. A similar approach as the original UK requirements was adopted, allowing 100% clearway credit for the wet runway engine-out case, although using a V STOP and a V GO speed instead of a single V 1 speed. Orange Paper 25/88/1 was included in JAR 25 Change 13 (effective 5 th October 1989). The equivalent of FAA NPRM 93-8 being JAA NPA 25BDG244 was adopted as part of JAR 25 Change 15 (effective 1 st October 2000) which denies clearway credit for the engine-out case on a wet runway. In summary the following differences in clearway credit can be distinguished: Requirement AEO dry OEI dry AEO wet OEI wet FAR 25/0 50% 50% N/A N/A FAR 25/92 50% 50% 50% 0% JAR 25/1 50% 50% N/A N/A JAR 25/2 50% 50% 50% 100% JAR 25/5 UK 50% 50% 50% 100% JAR 25/13 50% 50% 50% 100% JAR 25/15 50% 50% 50% 0% Current JAR-OPS rules do not have additional retroactive requirements. DNPA-OPS 47 developed by the JAA Performance Subcommittee however intends to retroactively prohibit clearway credit for the engine-out case on wet runways. According to Boeing the following OEI wet runway clearway credit is available: 747-400: 100% 777-200/300: 50% (halfway between the IFALPA position and applicable requirement) 777-300ER/200LR: 0% 737PG: Work around by applying Slippery Performance (Good/Wet) 737NG: 0% (certified including JAA NPA 25BDG244)
Improved Climb By increasing the climb speed climb out performance may be increased at the expense of field performance thereby optimising the performance limited weight when limited by climb requirements. Increased takeoff speed should still comply with brake energy and tire speed requirements: Source: Boeing Flight Operations Engineering
Appendix 2: Takeoff Accidents resulting from inadequate performance MK Airlines Limited Boeing 747-244SF On 14 October 2004, an MK Airlines Limited Boeing 747-244SF was being operated as a nonscheduled international cargo flight from Halifax, Nova Scotia, to Zaragoza, Spain. At about 0654 coordinated universal time, MK Airlines Limited Flight 1602 attempted to take off from Runway 24 at the Halifax International Airport. The aircraft overshot the end of the runway for a distance of 825 feet, became airborne for 325 feet and then struck an earthen berm. The aircraft's tail section broke away from the fuselage, and the aircraft remained in the air for another 1200 feet before it struck terrain and burst into flames. The aircraft was destroyed by impact forces and a severe postcrash fire. All seven crew members suffered fatal injuries. In this accident, the flight crew's take-off performance calculations resulted in an error that remained undetected until the aircraft reached a point where the crew's response was too late to avert the accident. Source: Transportation Safety Board of Canada, Accident Report A04H0004 Other Accidents; a review by the Transportation Safety Board of Canada A review of large (above 5700 kg), turbine-powered aircraft accident and incident data has shown that there have been at least 12 major occurrences where take-off performance was significantly different from scheduled performance. Four of the aircraft involved were destroyed and there were 297 fatalities. Several of these occurrences involved flight crews that attempted a take-off using incorrect performance data, and then did not recognize the inadequate take-off performance of the aircraft. There were other accidents where the take-off performance has been inadequate because of mechanical failures, incorrect aircraft configuration or incorrect instrument indications. These occurrences were not isolated to any particular aircraft type, commercial operation or geographic area. Underlying most of these occurrences were one or both of the following safety issues: The failure or absence of procedural defences to detect an error in the take-off performance data; and The failure of the crews to recognize abnormal performance once the take-off had commenced. The following are some representative accidents taken from the data: On 12 March 2003, a Boeing 747-412 suffered a tail strike on take-off in Auckland, New Zealand, and became airborne just above the stall speed (New Zealand Investigation 03 003). The aft pressure bulkhead was severely damaged, but the crew managed to land safely. The cause of the tail strike was a result of the flight crew entering a take-off weight
100 tonnes less than the actual weight into the flight management system, resulting in low take-off speeds being generated. There was no crew cross-checking of the speeds. On 11 March 2003, a Boeing 747-300 in Johannesburg had a tail strike on take-off (NTSB report DCA03WA031 refers). The flight engineer had entered the zero fuel weight of 203 580 kg instead of the take-off weight of 324 456 kg into the hand-held performance computer, and then transferred the incorrect computed take-off speeds onto the take-off cards. On 14 June 2002, an Airbus A330 had a tail strike on take-off in Frankfurt, Germany, because incorrect take-off data were entered into the flight management system (TSB report A02F0069 refers). The tail strike was undetected by the flight crew, but they were notified by air traffic services during the climb-out. The aircraft sustained substantial structural damage to the underside of the tail. On 28 December 2001, a B747-200 cargo aircraft had a tail strike on take-off in Anchorage, Alaska, and sustained substantial damage (NTSB report ANC02LA008 refers). The crew did not account for the weight of the additional fuel (about 45 360 kg) taken on board in Anchorage, and inadvertently used the same performance cards that were used for the previous landing. The crew members were unaware that the tail had struck the runway until after arrival at their destination. On 13 January 1982, a Boeing 737-222 was on a scheduled flight from Washington, DC, to Fort Lauderdale, Florida. During take-off, the EPRs were set for 2.04, and on the take-off run, anomalous engine instrument readings were noted; the captain elected to continue the take-off. Approximately 2000 feet and 15 seconds past the normal take-off point, the aircraft became airborne. The aircraft initially climbed, but failed to accelerate. The stall warning stick shaker activated shortly after take-off and continued until the aircraft settled, hit the 14th Street Bridge and several vehicles, then plunged into the frozen Potomac River. The investigation revealed that the engine inlet pressure probes became blocked with ice, resulting in high EPR indications. Of the 79 persons on board, 74 perished, and there were four ground fatalities. From at least as far back as 1972, there have been safety recommendations and initiatives to ensure that crews have a reliable on-board method of detecting abnormal take-off performance, particularly in situations where performance is less than required or expected. Unfortunately, there is still not a reliable in-cockpit system available for crews to detect and react to abnormal take-off performance in a timely manner. Source: Transportation Safety Board of Canada