Qantas has been proving FANS equipment and refining procedures.


AIRLINE PLANNERS AND civil-aviation authorities understand the long-term benefits of future-air-navigation-systems (FANS) technology. Early unease among pilot unions over reduced separation standards and other aspects, however, suggests that some line crews may have been kept less fully informed. To assess the way FANS affects the line pilot's working environment, Flight International was aboard the first pre-implementation Boeing 747-400 FANS 1 demonstration flight, a direct Qantas revenue service from Sydney to Los Angeles, immediately following type certification by the US Federal Aviation Administration and Australia's Civil Aviation Authority (ACAA).

"The purpose of this flight was to demonstrate to the world, that the system is here and that it's up and running" says, Capt David Massy-Greene of Qantas, who was aboard as an observer, along with a Boeing, SITA and Honeywell team, returning from work in Australia on the final type certification.

Although the flight was primarily report-and-controlled on high-frequency (HF) radio, all activities and functions were duplicated on datalink, meaning that the crew workload was increased, rather than diminished as it will be under fully operational FANS procedures. This account describes a typical FANS operation rather than the proving flight specifically.


FANS operation begins at the gate, with standard instrument departure and airways clearances uploaded to the flight-management system (FMS) following pre-flight "log-on" to the ACAA's ground terminal in Canberra. That procedure, which requires only about 20 keystrokes, also activates the automatic-dependent-surveillance (ADS) function. From that point, the aircraft's flight-management system (FMS) begins its uncommanded reporting to air-traffic-control (ATC), where the aircraft's position is continually "painted" on a terminal resembling a modern radar display unit. In-flight log-on (normally only necessary for non-normal communications such as revised clearance requests) requires about 30 keystrokes.

Because FANS/ADS operation is simply another function of the software-updated FMS, it requires no additional crew-training time. The visible changes evident to the crew are virtually all in the software, and appear as modifications to a few pages of the FMS. Hardware additions include dual global-positioning system receivers and satellite-communications (satcom) capability. A flight deck printer, required for FANS 1 operation, is a standard fit on 747-400s.

Flight planning has already indicated the chosen "flex-track" route, confirmed by the uploaded clearance, which will take the flight some 1,880km (1,020nm) to the south of its return route. The difference on this flight will represent a 30min saving on the great circle route, despite the route distance of 12,500km, which exceeds the great-circle distance by 485km.

The plan, or any of its details, can be set up on the navigation display (ND) for review, with a hard copy available from the flight deck printer. To upgrade the plan from inactive to active status in the FMS, the captain simply presses the "accept" key from the menu options, and the plan then becomes the primary navigation command to the autopilot and flight director.

Other options offered are "Reject" or "Standby" and, if the system is requested to reach an altitude within specifications outside the aircraft's physical capability, it will issue a message such as: "Unable. Next alt". Acceptance of the clearance sends a "Wilco" message, which closes the loop because the acknowledgment has the same reference number as the original transmission, so that ATC knows that the message has been accepted.

Taxi and take-off clearances are still verbal, but ARINC has a proposal to datalink them, too, during 1996. No post-departure call is normally required and, on climb, crews will also appreciate the silence, which replaces the customary frequent ATC requests for reports passing through levels. An aircraft 130km ahead on the same route, which would have delayed the climb under conventional ATC procedures, would now cause no restriction on initial climb.


It is when the flight is beyond VHF navigation and communications range that the pilot benefits of ADS are fully appreciated. The multiple factors compelling controllers to build an ever-growing conflict-resolution zone around aircraft in oceanic airspace include the non- availability of VHF navigation aids to update inertial-reference systems; provision for the contingency of protracted loss of communications; and the "blunder factor", by which a crew may overlook planned course changes at waypoints, or may make an incorrect course change.

On this flight, actual navigation performance never exceeded a maximum theoretically possible 111m position error The end result is that the information available to controllers (including a zoom function) is of higher quality, precision and integrity monitoring even than that now available in terminal-area radar environments, and will clearly be proved by current appraisal to be more than capable of supporting the ultimately planned 55km along-track and lateral separation. Inherently, because it is based on grid winds and ground speed advantages, the dynamic air route planning system also guarantees that all traffic on a given track will be flying in the same direction.

"One of the big differences between ADS and radar is that radar says: 'Here I am and this is where I've been', while ADS says: 'Here I am and this is where I'm going'. That's gold to an air-traffic controller and, ultimately, it's possible to build variable conflict zones around various aeroplanes depending on their capability," says Massy-Greene.

The flight demonstrated the practicality, attractive to pilots, of not once, for over 12h, having to pick up a microphone and do battle on HF with the mercurial ionosphere - a goal which will be reached when the US Federal Aviation Administration has ADS available, about mid-1996, for datalinked position reports. Pilots who fear that sustained inactivity may create a situational-awareness gap when a crew is given a revised flight plan in mid-Pacific, can be reassured by an experiment conducted during the flight. A re-generated route clearance and flight plan, developed by the US Oakland Centre's dynamic ocean-tracking system, was uplinked by Auckland. The ND can display the current flight-plan route, along with that of the newly proffered version, including off-track navigation aids, en route and diversion airfields, and revised fuel reserves on arrival. In the re-routing process, all calculations of critical points, equal time points, points of no return and divert points are incorporated in the revised flight plan, based on the new flight path.

The destinations of messages to and from the flight, and the frequency of ADS reports, are determined by the ATC system. They are normally invisible to the flight crew, but can be displayed at will. To minimise cost (SITA has not yet disclosed its pricing, but is expected to be about A$1.00 [76¢] per satcom ADS report), the system also automatically selects VHF as the communications medium when the flight is in range. Message handling is not complex, with standard messages such as clearance requests pre-formatted so that the crew needs only to fill in the blanks on the "ATC datalink" page.

As ADS becomes the norm on transpacific routes, the question of separating FANS 1-equipped aircraft from those using conventional communications and navigation will be highlighted, says Massy-Greene: "It's really a question of RNP [required-navigation-performance] and non-RNP aircraft. The only way it can be done is by declaring some routes to have an RNP requirement, similar to the MNPS [minimum navigation performance standards] requirement on the North Atlantic."

The threshold of system overload in the current satellite system is low, but manageable. When Inmarsat 3's directional antenna "spot-beam" system becomes available, each transponder will be capable of carrying 1,096 airborne aircraft. A spot beam is preferred over the global beam in current use.

"The flight really brings home the realities to the FAA technical centre in Atlantic City. They may have thought they had a bit longer, but there's now a live aeroplane here that wants to talk to them, and we're going to start saying that, as an airline, we want the benefits out of it. That will start from October onwards. Out of Los Angeles westbound, we have been re-routing virtually every flight, particularly the evening departure, because it leaves half an hour before the new forecast is issued, and the current forecast is 11h 30min old. A new forecast can quite substantially change the track."


Other carriers watching Pacific progress keenly, are beginning to realise FANS potential, according to Massy-Greene. "The advantages are almost impossible to ignore, although I think some people doubt we'll achieve all the benefits we're planning on. There's still air-traffic-controller training; there are ground systems to be installed; and, while all that can be done very quickly, there's a whole stack of institutional matters to be overcome too, in terms of such aspects as FIR crossing points - where do you cross the boundaries of national airspace?"

Massy-Greene's insistence on cost benefits have driven the development parameters of FANS 1. While FANS 1 users have been guaranteed "backward compatibility", he is nevertheless convinced that further development will be imperative. "FANS 2, 3 and 4 are inevitable, because we'll find things we should have done. Some things were deliberately left out of this stage because of the development time involved, some were left out because of cost, because we couldn't see short-term benefits, and because we can't afford throwaway software," he says.

The datalink repertoire is almost certain to change, he says. "We're finding that the datalink library we have now could do with some more capability in terms of message content. For example, there is no message currently to report maintaining an altitude at the pilot's own volition; it has to come up from the ground," he says. Massy-Greene has also noted that, in terms of separation standards, "...the distance report doesn't contain seconds, but only whole minutes". At the speeds, the aircraft are being flown, that is between 14.8km and 18.5km, " the time report is too coarse."

Some of the development has been limited by the computing power of the current FMS and, in time, there will be a new FMS with more computing power, but, that will be driven by the benefits, Massy-Greene says. "We're way beyond the stage where the flight-operations departments of airlines could say: 'That seems like a nice idea, let's do it'. We had to do an in-depth cost-benefit analysis on what we're going to get from it all, and whether it would meet our corporate-payback periods. The answer was yes, it does," he says.

Source: Flight International