Trajectory-based ops pair new tech and flying basics

 - August 2, 2010, 5:23 AM

Now that we’ve all gotten accustomed to acronyms like Rnav, RNP, LPV and all the others, the next big game changer will be TBO, for trajectory-based operations, sometimes loosely thought of as user-preferred trajectories. Oddly enough, trajectory flying was the fundamental technique used way back by pilots flying the mail in their biplanes and in early passenger operations. Load up, start up, taxi out, take off, climb, cruise and descend along the most direct route at the preferred speed and altitude, and then land and taxi in, all with minimum or no delay.

But then someone invented the low-frequency A/N radio range tied to things called airways and, old timers undoubtedly felt, it was downhill from then on. There’s a grain of truth in that. Flights between major centers in the 1920s that took, say, two hours at an average of 110 knots can now take around the same time at an average of 400 knots, and still have a hard time meeting the schedule.

Hence the coming move to trajectory operations where, with the help of advanced technology, we will return to the way it all began. But getting to that point will not be as simple as before, speakers emphasized at the annual technical symposium sponsored by the FAA and Air Traffic Control Association at Atlantic City in May.
Safety is the prime consideration, of course. Yet with many more aircraft in the world’s skies–36,000 in 2025 versus around 22,000 today, according to similar Airbus and Boeing estimates–and with more than three-quarters of the future fleet carrying advanced-technology avionics, the pressure on air traffic management will be intense.

First, voice communications will no longer be adequate or effective, and by 2018 will be largely superseded by digital data communications, or DataComm, now under development, where clearances and other instructions will arrive via the FMS, with their messages displayed for pilot acceptance or rejection. When DataComm is fully integrated by 2025, messages will neither be created nor inserted for transmission by controllers. By then, those tasks will be performed by the system’s automation from its knowledge of all other aircraft movements and all other things relevant to them.

In fact, the automation won’t even know the word “aircraft.” By NextGen’s forecast end state in 2025, your sleek new machine and its intended operation will have become a “flight object,” with its trajectory profile determined by the automation, after consideration of a host of different influences such as other traffic, en route and destination weather, airspace availability versus time, individual aircraft equipage and operating capabilities in the several flight phases. The preferences of the owner’s flight operations department regarding things like economy or high-speed cruise, required fuel, weight, acceptable departure and arrival time “windows,” diversion airports and similar factors will also be included in the development of the trajectory profile.

A Smarter Aircraft
Interestingly, most conference presentations on trajectory operations these days, including those at the FAA/ATCA Symposium, describe the automation aspects in detail but rarely cover the pilots’ functions. Perhaps the pilot’s role will simply be typing “N-12345 JFK-LAX, please” on the automation’s input device.

What avionics will your aircraft carry? DataComm, of course, and a much more advanced flight management system than most aircraft carry today. You’ll have ADS-B in, with its presentation of other aircraft probably integrated, or “fused” with Tcas, where ADS-B gives longer-range TAs and Tcas provides the RAs. The
ADS-B’s transmissions will likely also include intent and other messages not sent today. The aircraft’s altimetry system will also probably be more advanced than today’s RVSM standard, with the likely addition of GPS/GNSS altitude, since by then there could be 50 or more navigation satellites in orbit.

Rnav and RNP will be standard, but with RNP 0.1 expected to be the typical requirement for entry into the future super-density terminal and high-altitude airspace where traffic separations are anticipated to be much closer than today. Some specialists forecast a new vertical RNP capability on the grounds that while conventional RNP would be satisfactory for level cruise, it will probably not be precise enough for climbs, due to less predictable climb rates, winds, groundspeeds and temperatures with the changes in altitude, coupled with the tight vertical and lateral limits of the assigned “windows” of the climb corridors, which would also be constraints in climbing passing maneuvers.

Vertical RNP would also play an important role in maintaining post-takeoff departure routings, which are expected to form a widespread fan-shaped array of tracks shortly after liftoff, minimizing wake turbulence effects from earlier departures and allowing shorter intervals between them.

The en route domain will be monitored by advanced versions of today’s conflict probes, with their data going to the ground automation system that will continuously check individual track-keeping compliance and issue track corrections when necessary to the FMS for crew acceptance. This would also be the case should a weather system move onto the planned trajectory track, requiring a heading change to avoid it, followed by a return to the planned track. Heading changes calculated by the automation would be sent to the FMS as radii of the RF turn required to accomplish the required maneuver precisely.

Timekeeping will be critical throughout, monitored by the automation and exercised through required time of arrival (RTA) commands to the FMS. RTA adherence will be particularly important during the descent phase, where several aircraft will merge and in-trail spacing will reduce. With full automation control, today’s continuous descent arrival procedures will probably more closely resemble the somewhat more flexible tailored arrivals developed for oceanic operations, and which integrate lower-altitude domestic arrivals into the traffic flow.

It will certainly be a different, more efficient, world, with clear benefits in safety, time and fuel savings and reductions in emissions. Its effect on pilot job satisfaction is perhaps quite a different question.   

First Garmin G500H Installed 

Edwards & Associates has outfitted the first helicopter with a Garmin G500H glass cockpit–a Bell 407 delivered to New York’s Zip Aviation earlier this summer.
The G500H includes helicopter synthetic vision technology and XM WX satellite weather with Nexrad. The avionics primary flight display shows attitude, airspeed, vertical speed, altitude and course/heading information, while the multifunction display can present the helicopter’s current position in relation to terrain, aeronautical chart data, navigation aids and flight plan routings. The G500H is integrated with the aircraft’s Garmin GNS 530W navigation/communications radio, which can navigate using GPS and Waas signals.    –M.H.