Flight management systems have evolved to a level of sophistication that helps flight crews fly commercial airplanes more safely and efficiently. 20 aero QUarterlY Qtr_02 | 09 Contribution of Flight Systems to Performance-Based Navigation Flight Management Systems (FMS) and associated airplane flight systems are the primary navigation tools on board today’s commercial airplanes. The evolution of these systems has led the way for performance-based navigation (PBN) and the U.S. Federal Aviation Administration’s (FAA) Next Generation Air Transportation System. By Sam Miller, Associate Technical Fellow, Flight Deck, Flight Crew Operations PBN is a concept used to describe naviga- concept is made possible largely by aviators to fly coast to coast across the tion performance along a route, procedure, advances in the capabilities of airplane FMS. United States. However, these early flights or airspace within the bounds of which This article helps operators better were filled with uncertainties and their use the airplane must operate. For transport understand how the FMS and other of visual flight rules soon gave way to airplanes, it typically is specified in terms airplane flight systems have evolved over reliable attitude indicators and ground- of required navigation performance (RNP). time, how they contribute to PBN opera- based navigation aids, or navaids. Non- The PBN concept defines navigation tions, and plans for further advancement. directional radio beacons and the airplane’s performance in terms of accuracy, integrity, airborne automatic direction finder equip- availability, continuity, and functionality. ment allowed aviators to “home in” on the AIR NAVIGATION toolS leADING up These operations provide a basis for to the FMS beacon and navigate reliably from station to designing and implementing automated station. Non-directional radio beacons are flight paths that will facilitate airspace design, still being used today throughout the world. Early aviators relied on very basic instru- terminal area procedure design, traffic flow In the 1940s, the introduction of a mentation to keep the airplane upright and capacity, and improved access to runways radio-magnetic indicator or dual-bearing navigating toward the desired destination. (more information about PBN can be found distance-heading indicator facilitated the Early “turn and slip” indicators and ground in AERO second-quarter 2008). The PBN use of ground-based navaids, including references such as lighted beacons enabled 21 WWW.boeIng.com/commercIal/aeromagaZIne Figure 1: Typical VOR installation By 1952, more than 45,000 miles of airways using the VOR were in operation. A DME transmitter was usually located on the ground with VOR 15 DME stations. DME transmitters would respond to interrogation by transceiver equipment installed on airplanes and provide the pilot with a reliable 360º distance in nautical miles to the transmitter. Pilots operating in areas where VOR and DME coverage was available had both distance and course 270º 90º information readily available. 270-degree Radial 180º VOR/DME the very-high-frequency omni-directional on the 727, 707, and 747-100. During this While Boeing was continuing work on range (VOR) navigation system and dis- same time, Collins produced the AINS-70, new commercial airplane navigation systems tance measuring equipment (DME). VORs an area navigation (RNAV) computer on the for the new “glass” flight decks, a debate came into wide use in the 1950s and DC-10. Each of these steps reduced the was under way among the airlines about quickly became the preferred navigation amount of interpretation by the flight crew the need for a dedicated flight engineer radio aid for flying airways and instrument by presenting more specific indications of crewmember. In July 1981, an industry task approaches (see fig. 1). VOR and DME airplane positional and situational status. force determined that two-crew operation provided the framework for a permanent Even so, the reliance on the flight crew to was no less safe than three-crew operation. network of low-altitude victor airways manually interpret and integrate flight This decision would have a profound effect (e.g., V-4) and high-altitude jet routes information still provided opportunities for on the design of all Boeing commercial (e.g., J-2), which are still in place today. operational errors. airplanes, including a short-notice imple- Long-range navigation over remote mentation for the new 767. With one fewer and oceanic areas, where navigation radio crewmember, Boeing engineers focused on The FIRST INtegrAted flIght transmitters did not exist, was originally MANAgeMENT coMputer a flight deck design that would reduce crew accomplished by dead reckoning and workload, simplify older piloting functions, celestial navigation. The introduction of the and enhance flight deck efficiencies. When Boeing began work on the 767 inertial navigation system (INS) on airplanes The early 767 FMC provided airplane airplane program in the late 1970s, the facilitated long-range capability by providing performance predictions using stored company created a flight deck technology a continuous calculation and display of the airframe/engine data and real-time inputs group with engineers dedicated to the airplane’s position. Flight crews could enter from other onboard systems, such as the development of the flight management waypoints and the INS would calculate air data computer and inertial reference computer (FMC) and the control display heading, distance, and estimated time of system (IRS). This performance function unit (CDU) (see fig. 2). Boeing merged arrival to the respective waypoint. replaced flight crew back-of-the-envelope- previous designs of the performance At the same time, the 1970s fuel crisis type estimates with relatively precise time management computer and the navigation provided the drive to optimize navigation and fuel predictions based upon actual computer into a single FMC that integrated capabilities in commercial airplanes. As airplane performance parameters, such as many functions beyond navigation and a result, avionics manufacturers began gross weight, speed, altitude, temperature, performance operations. The company producing performance management and winds. used experience gained from Boeing’s other computers and navigation computers to Then, as now, the navigation function research projects to develop advanced help operators improve the efficiency of was based on the IRS position and used implementations of performance manage- their airline operations. Boeing’s initial entry ground-based navaids (e.g., DMEs, VORs, ment functions and navigation into a into this arena was represented by the localizers) to refine the IRS position and single FMC. The new FMC system was implementation of the early Sperry (now correct for IRS drift. A navigation database envisioned as the heart of an airplane’s Honeywell) automatic navigation systems (NDB) was included in the FMC’s memory flight planning and navigation function. 22 aero QUarterlY Qtr_02 | 09 Figure 2: 757/767 FMC CDU One of the first implementations of an FMC CDU was designed for the 757 and 767 in the early 1980s. and contained approximately 100 kilobytes For several years following the initial of data consisting of navaids, airways, FMS certifications, minor changes were approach procedures, and airports. The made to enhance the FMS operation, NDB allowed flight crews to easily enter but no significant hardware or software flight plans from takeoff to landing and changes were made until the early 1990s. make real-time route changes in response to air traffic control (ATC) clearances. The DEVelopING the ModerN FMC FMC also provided guidance to the flight plan route using the lateral navigation (LNAV) In the late 1980s and 1990s, the airline and vertical navigation (VNAV) functions. industry requested the capability of direct Initially, the FMC was equipped with LNAV routing from one location to another, only. VNAV was a new challenge and without the need to follow airways based required a significant effort on the part upon ground-based navaids. Modern of Boeing and Sperry (now Honeywell) FMS equipped with a multi-sensor navi- engineers to make the vertical guidance gation algorithm for airplane position component operational. determi nation using VOR, DME, localizer, After the development of the 757 and and IRS data made this possible, and 767, Boeing also worked with Smiths RNAV was transformed from concept to Aerospace (now GE Aviation) to develop operational reality. an FMC as part of a major update to the But oceanic operations and flight 737 family. The operation of the 737 FMC, over remote areas — where multi-sensor the appearance of the CDU, and the CDU updating of the FMC could not occur menu structure were designed to parallel with accuracy better than the drift of IRS those on the 757 and 767. The FMC systems — made RNAV operations difficult. became part of the design of the 737 Operations in these areas of the world were Classic family, which included the 737-300, increasing during the 1990s, and there was 737-400, and 737-500. The 737-300 was pressure on avionics suppliers, airplane the first of the family to be certified in 1984. manufacturers, and regulatory agencies Boeing offered the 737 Classic family with to find a way to support precise navigation either single or dual FMCs and with either in remote and oceanic areas. As a result, the traditional electro-mechanical attitude the concept of a future air navigation director indicator/horizontal situation system (FANS) was conceived in the early indication flight instrument suite or the 1990s (see AERO second-quarter 1998). EADI/EHSI “glass” flight deck derived Subsequently, Boeing and Honeywell from the 757/767 design. introduced the first FANS 1-capable FMC 23 WWW.boeIng.com/commercIal/aeromagaZIne An RNP system should contain both performance monitoring and alerting: a caution alert is initiated by the FMC and annunciated on the display system to draw flight crew attention in the event that ANP exceeds RNP. on the 747-400. At the heart of the system to the flight crew when this containment RNP: ENAbler of PBN was a new, more capable FMC that might not be assured.