Albert A. Herndon

Use of lateral/parallel FMS procedures and implementation issues

The lateral offset operation allows a trailing aircraft to overtake a leading aircraft (subject to clearance by air traffic control [ATC]), by: turning off course, intercepting a parallel route, effecting the overtake, and then, optionally returning to course. Alternately, the leading aircraft could perform the offset, allowing the trailing aircraft to pass while staying on course. With modern flight management computers (FMCs), the procedure is easily performed with just a few button pushes. In a previous presentation at this forum, testing at Albuquerque and Houston air route traffic control centers (ARTCCs) was described. That testing demonstrated the feasibility and general acceptance of the procedure. Controllers and pilots were able to agree on phraseology, angle of turn, etc. Controllers at adjoining facilities were able to coordinate to allow boundary crossing of flights on the parallel offset route. Recent testing at the Minneapolis ARTCC extended these tests. Whereas the initial tests demonstrated feasibility, the Minneapolis test was designed to demonstrate benefits. For flights westbound from Minneapolis-St. Paul International Airport, faster, trailing aircraft were able to be offset and overtake slower, leading aircraft. Although there was ample airspace to solve these situations using other techniques (e.g., turn-out, then direct), we were able to compute a provisional benefit of the lateral offset procedure, probably most applicable to more constrained airspace conditions. This paper will describe the test and present numerical results of time and distance savings, and the subjective responses of air traffic controllers surveyed at the end of the test.

Estimated Time Of Arrival (ETA) performance system comparative evaluation

As the United States (U.S.) moves toward the various phases of Next Generation Air Transportation System (NextGen), there will be more emphasis on control of aircraft using time as well as the traditional speed control. With this in mind, Radio Technical Commission for Aeronautics (RTCA) was directed by Federal Aviation Administration (FAA) in 2012 to revisit the Minimum Aviation System Performance Standards (MASPS): Required Navigation Performance (RNP) for Area Navigation (RNAV), DO-236B [1], to update the requirements for RNP RNAV systems based on lessons learned from implementing Performance Based Navigation (PBN). The committee was also asked to consider a forward look/refinement of the time-based requirements for systems. The RNP RNAV system performance standard DO-236C [2] Change 1 [3] amended existing standards from DO-236B by expanding the minimum requirement for system computed Estimated Time of Arrival (ETA) in a Flight Management System (FMS). The new minimum functional requirement is that the ETA must be available for each fix in a flight plan; the previous minimum only required ETA at the “go to” fix. In an important addition, DO-236C Change 1 sets a minimum performance requirement on ETAs at all planned (future) fixes in the onboard flight profile. Thus the standard has been expanded both in the functional and the performance requirements for ETA in an RNP RNAV system.

Performance-based navigation fleet equipage evolution

As fleet avionics continue to evolve, the use of the solutions provided by performance-based navigation (PBN) will continue to grow and provide benefits to the aircraft operators. Due to these potential benefits, several air carriers in the United States have announced plans to retro-fit their fleets with PBN capabilities. However, it is important to understand the current snapshot of avionics, as well as the historic growth before analyzing the future forward-fit scenarios. Since 2004, the MITRE Corporations Center for Advanced Aviation System Development (CAASD) has monitored the navigational avionics for Part 121 United States airlines. In this time span, the number of Part 121 airframes has dropped by more than 400 aircraft while the number of Part 121 aircraft with a flight management computer (FMC) has grown at approximately the same rate. This has resulted in a fleet wide growth in the percent of aircraft operating with an FMC from 79% to 90%. Also, the number of aircraft operating with a Global Positioning System (GPS) (also known as Global Navigation Satellite System (GNSS) navigational sensor) has grown with 1,100 additional aircraft operating with a GNSS sensor today. This has resulted in a growth from 47% of the aircraft in 2004 to 66% of the aircraft. There have been three primary reasons for the growth of PBN operational capability: equipped aircraft delivered to the system, current fleet retro-fits, and new knowledge of the airline operators. This paper will discuss the current equipage trends, capability, and identify the evolutionary change in Part 121 PBN avionics from 2004 through 2008. Additionally, this paper will discuss the next generation of aircraft and potential future scenarios for fleet avionics.

Use of magnetic variation and station declination for heading (VX) and course (CX) leg types

Leg types, also known as path terminators, are used in aircraft navigation to define paths as routes for RNAV equipped aircraft. Many leg types are specifically defined to cause the Area Navigation (RNAV) system to emulate the actions that an aircrew would take when flying the route manually based on the text and other depictions on the chart. Some emulate magnetic headings or courses, which, for various reasons, can lead to differences between what the procedure designer intended and what the RNAV system displays or flies. Two in particular are in common use individually and in combination, and this paper will explore the potential for unexpected differences in the resulting paths. These two are the heading type (Vx) which may be used where the procedure or airspace designer calls for a heading to some type of termination, and the Course type (Cx) which may be used where designers wish to fix the aircraft path over the ground using a course defined by a navigational aid (NAVAID). Issues arise because of the need to implement magnetic courses and headings in an RNAV system that navigates in a true north reference frame. Given that the Earths magnetic field orientation varies with location on the Earth (hence true north and magnetic north change relative to each other), changes with time, and that NAVAIDS and runways are marked/oriented in the magnetic reference frame of the time they are surveyed, care must be taken to make the RNAV system emulate the procedure intent; this paper will describe and summarize those cautions and issues.

A separation standard for departures transitioning from terminal to en route control

The advent of radar surveillance over half a century ago enabled numerous Air Traffic Control (ATC) standards that continue to be in use today to safely separate aircraft. In the case of departure operations, the discrete increase of spacing requirements that applies when transitioning from terminal to en route control hampers Next Generation Air Transportation System (NextGen) goals of improving operational efficiencies. This paper proposes the concept of the Established-on-Departure Operation, or EDO, standard that capitalizes on improved navigational precision of Performance Based Navigation (PBN) operations. The concept incorporates current diverging procedures permitted in the terminal area as well as the concept of reduced divergence. The paper describes the requirements for its application and presents the analysis carried out to extend the applicability of a previously proposed standard for reduced-divergence operations. For Area Navigation (RNAV) Standard Instrument Departure (SID) operations, the analysis conservatively quantified a reduced divergence angle of 9 degrees, a 40-percent reduction in angular divergence when compared to todays 15-degree requirement. In order to illustrate implementation examples and estimate potential benefits, the concepts were applied to the RNAV SID structure at The Hartsfield-Jackson Atlanta International Airport (ATL). For ATL alone, the estimates show a potential annual benefit of approximately

Analysis of advanced flight management systems (FMS), flight management computer (FMC) field observations trials, vertical path

1.6 million per year. The standard concepts offer a suite of additional procedure design options not currently available to better accommodate airspace constraints and to increase the efficiency of departure operations transitioning from terminal to en route control.