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.