NationaalNa Lucht- en Ruimtevaartlaboratorium NLR-TP-2001-003 Safety aspects of tailwind operationsSafety operations G.W.H. van Es and A.K. Karwal Nationaal Lucht- en Ruimtevaartlaboratorium National Aerospace Laboratory NLR NLR-TP-2001-003 Safety aspects of tailwind operations G.W.H. van Es and A.K. Karwal This report is based on a presentation held on the Flight Safety Foundation Annual European Aviation Safety Seminar, Amsterdam, The Netherlands on 12-14 March, 2001. The contents of this report may be cited on condition that full credit is given to NLR and the authors. Division: Air Transport Issued: January 2001 Classification of title: Unclassified -3- NLR-TP-2001-003 Summary In the present study the safety aspects of aircraft takeoff and landing operations in tailwinds are explored. The study covers a description of legislative instruments that influence preferential runway selection in relation to the maximum tailwind component applied; tailwind certification issues; and relevant safety issues concerning tailwind operations in general. Also a systematic analysis of historical tailwind related overrun accidents and incidents is presented. Some of the important findings of this study are: • In many of the analysed accidents the actual tailwind exceeded the approved limit. • The tailwind component determined by the Flight Management System (FMS) appears to be relatively insensitive to common FMS errors. • Present-day wake vortex separation criteria for final approach may be insufficient in light tailwind conditions. • Operating on wet or contaminated runways in combination with a tailwind yields a high risk of an overrun. • Current certification requirements of operations in tailwinds greater than 10 Knots are limited to guidelines in the Flight Test Guide. -4- NLR-TP-2001-003 Contents 1 Introduction 6 2 Legislation, standards and recommendations 6 2.1 Runway selection 6 2.1.1 ICAO recommendation for noise preferential runways 6 2.1.2 FAA recommendation for noise preferential runways 6 2.2 Aircraft certification 7 2.3 Aircraft takeoff and landing performance information 10 3 Operational issues 10 3.1 Effect of tailwind on field performance 10 3.2 Tailwind during the approach 11 3.2.1 Speed, path and configuration control 11 3.2.2 Rate of descent 12 3.3 Floating during landing 13 3.4 Wake vortices and tailwind 13 3.4.1 Approach 13 3.4.2 Landing 13 3.5 Wind information available to the flight crew 14 3.5.1 ATIS wind reporting 14 3.5.2 Tower wind reporting 15 3.5.3 FMS wind 15 4 Analysis of tailwind related overrun events 16 4.1 Phase of flight 16 4.2 Runway surface condition 17 4.3 Excessive approach speed 17 4.4 Floating during landing flare 18 4.5 Tailwind conditions 19 5 Conclusions and recommendations 20 5.1 Conclusions 20 5.2 Recommendations 20 6 References 21 -5- NLR-TP-2001-003 Appendix A: PANS-OPS Doc 8168-OPS/611, Chapter 2.1 22 Appendix B: FAA Order 7110.65L: Air Traffic Control 23 Appendix C: FAA Order 8400.9: National Safety and Operational Criteria for Runway Use Programs 24 Appendix D: Flight Test Guide FAA AC 25-7A (31/3/98) 25 (26 pages in total) -6- NLR-TP-2001-003 1 Introduction The present study will explore the safety aspects of aircraft takeoff and landing operations in tailwinds. Legislative instruments and the maximum tailwind component that influence preferential runway selection at airports are explored. Certification of tailwind operations is reviewed in detail. The relevant safety issues concerning tailwind operations are reviewed and discussed. Finally a systematic analysis of historical tailwind related overrun accidents and incidents is presented. The basic objective of the present study is to get a general understanding of the issues that play a role in the safety of tailwind operations. 2 Legislation, standards and recommendations 2.1 Runway selection World-wide more than 300 airports have a noise preferential runway system. There are international recommendations regarding the runway assignment process and the maximum tailwind component used in selecting the preferred runway: a recommendation by the International Civil Aviation Organisation (ICAO) and a recommendation by the Federal Aviation Authorities (FAA). 2.1.1 ICAO recommendation for noise preferential runways In the PANS-OPS1 document, ICAO recommends a maximum tailwind for runway selection of 5 Knots including gusts (see Appendix A). The guidance material provided in PANS-OPS does not carry the status afforded to Standards and Recommended Practices (SARPs) adopted by the Council, and therefore does not come with the obligation imposed by Article 38 of the Convention to notify differences in the event of non-implementation. Furthermore SARPs are adopted by the Council as Annexes to the Convention, whereas guidance material such as the PANS-OPS are approved by the Council and are recommended to the contracting states for world-wide implementation. 2.1.2 FAA recommendation for noise preferential runways The FAA has published an Order that prescribes air traffic control procedures, including runway selection criteria. When no ‘runway use’2 program is in effect, FAA Order 7110.65L applies, see Appendix B. This Order prescribes the selection of the active runway as the one most 1 PROCEDURES FOR AIR NAVIGATION SERVICES-AIRCRAFT OPERATIONS. 2 Runway use program: A noise abatement runway selection plan designed to enhance noise abatement efforts. These plans are developed into runway use programs. Runway use programs are coordinated with the FAA. -7- NLR-TP-2001-003 aligned with the wind when the wind exceeds 5 Knots, effectively restricting the tailwind component to 5 Knots through runway selection. No reference is made to gusts. For runway use programs, FAA Order 7110.65L refers to another publication (FAA Order 8400.9 "National Safety and Operational Criteria for Runway Use Programs", see Appendix C). The purpose of FAA Order 8400.9 is to provide safety and operational criteria for runway use programs. These criteria are applicable to all runway use programs for turbojet aircraft. The Order provides parameters in the form of safety and operational criteria that must be used in the evaluation and/or approval of runway use programs. Regarding tailwind conditions, an important distinction is made here between dry and wet runways: for dry runways a tailwind component of 5 Knots (7 Knots if an anemometer is installed near the touchdown zone) may be present. For wet runways, no tailwind component may be present at all. Again, no instructions are given on how to interpret gusts that may exceed the given values. 2.2 Aircraft certification Under Federal Aviation Regulations FAR Part 25 or Joint Aviation Requirements JAR Part 25 no specific flight-testing is required for approval of operations in tailwind components of up to 10 Knots. Aircraft certified according to FAR/JAR Part 25 are therefore automatically approved for operations in tailwind components of up to 10 Knots. The origin of this 10 Knots tailwind limit can be found in Federal Aviation Administration (FAA) Civil Air Regulations release 60- 14, dated August 9, 1960. Specific flight-testing is required for approval of operations in tailwind components greater than 10 Knots. The requirements for these tests are not provided in the FAR/JAR Part 25. Currently only FAA Advisory Circular AC 25-7A (Flight Test Guide) gives guidance for the certification of tailwind operations greater than 10 Knots (see Appendix D). At present the FAA and the Joint Aviation Authorities (JAA) are trying to harmonise the FAA Flight Test Guide with the JAA equivalent. The section on tailwind certification is also under discussion. Although the work has not been finalised some of the important issues of this discussion are presented here (Ref. [1]): • For the certification of tailwind operations greater than 10 Knots, the FAA requires that testing is done with a tailwind greater than 150% of the value to be certified. Furthermore the FAA also states that an average tailwind should be used. When certifying tailwind operations of for instance 15 Knots, the "average" tailwind during flight testing must be 22.5 Knots (all wind speeds are measured at a height of 10 meters above the surface). In such conditions the wind is very gusty and the tailwind component can momentarily reach values of 30 Knots or higher. JAA considers such conditions as very severe and therefore proposed to amend the FAA guidelines on the 150% factor. -8- NLR-TP-2001-003 • The FAA considers that takeoff test flights with one engine inoperative should be conducted to show acceptable handling qualities during tailwind operations. The JAA does not consider this to be critical. Therefore this issue is still subject to discussion. During tailwind certification flight tests the measured wind data can come from the Inertial Navigation System (INS), tower, or portable ground recording stations (See Flight Test Guide for details). The wind data should be corrected to a 10-meter height. The tower wind contains a mean wind based on a two minute sample and (if high enough) a gusting wind value. Wind derived from the INS can include gusts depending on for instance the way the data are analysed. Among the aircraft manufactures different ways of analysing INS based wind data exist. Also engineering judgement is used in fairing the INS wind data which can introduce subjectivity into the results. An overview of tailwind limits obtained from available Aircraft Flight Manuals (AFMs) of a number of transport aircraft is given in table 1. The tailwind components are measured at or corrected to a 10-meter height. A large number of aircraft listed in table 1 have a tailwind limit of 15 Knots. This does not mean that all operators have approval to conduct takeoffs or landings with tailwind components greater than 10 Knots.