US freight carriers drive towards 'free flight'

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US freight carriers are gradually opting to equip with collision avoidance systems to meet foreign regulations, but the pioneering programme they initiated to develop better solutions at home remains on track.

The airlines are not affected by the long-standing US traffic alert and collision avoidance system (TCAS)-mandate, which applies only to passenger aircraft, but are having to equip at least some aircraft in order to meet European regulations in particular which will cover all large aircraft from 2000.

In the USA, however, the freight carriers have come under pressure from pilots’ unions and politicians to fit TCAS voluntarily.

But, because they expect eventually to have to equip for automatic dependent surveillance-broadcast (ADS-B), giving not just TCAS but some form of 'free flight' capability, they are investing in an extensive ADS-B research and development programme.

A dozen aircraft will begin flying in October with 'certified' avionics to explore the sort of ADS-B techniques that are expected to revolutionise air traffic control and navigation in the future.

The work, sponsored by the US Cargo Airline Association (CAA), will permit the simultaneous comparison of the three datalink technologies competing to be at the heart of any operational ADS-B network - Mode S; VHF Datalink Mode 4 (VDL-4 - also known as the Swedish STDMA system); and the Universal Access Transceiver (UAT) concept.

The programme is run by UPS-subsidiary IIMorrow, of Salem, Oregon where project manager, Craig Hudson, says: "We are moving ahead expeditiously. I think we have a lot of difficult tasks behind us."

Hudson says the team is on schedule for FAA "operational approval" of the on-board equipment on 2 October, having received "certification plan approval" from the FAA. Applications for supplemental type certificates to modify Boeing 727s and McDonnell Douglas DC-9s are under review by the Administration. "Box-level" integration is well underway and the validation and verification phase begins in a few days.

For the trial, IIMorrow intends to equip 12 in-service aircraft, comprising UPS and FedEx 727s and ABX Air DC-9s, plus the FAA Technical Center’s 727 and Convair 580.

The airborne equipment comprises: a link and display processing unit (LDPU); a datalink transponder linked to an external Global Positioning System (GPS) receiver; a 5in (127mm), Dzus-mounted, active-matrix LCD, cockpit display of traffic information (CDTI) made by Advanced Display Corporation of Atlanta; and a control unit.

Hudson says the programme will initially concentrate on air-to-air links with air/ground work being added later. The currently envisaged surface infrastructure would consist of five ground stations including the Dayton, Louisville and Memphis hubs of the three big parcel carriers, plus Scott AFB and one other in the same part of the USA.

The concept of ADS-B is that aircraft would datalink their three-dimensional positions, speeds and intents to each other and to the ground so that conflicts could be avoided automatically or by controller-intervention, leading to much more efficient use of airspace.

Operational use of ADS-B is some way off, however, and the CAA hopes that meanwhile the project can at least yield more sophisticated collision avoidance with the potential of full use of the technique later.

Hudson says the three increments are: first, to use the CDTI to assist pilots with visually acquiring conflicting traffic by accurately showing its location; second, the generation of warnings similar to the 'traffic advisories' generated by the current generation TCAS; and third, a markedly more capable "deconfliction" function, resembling the 'resolution advisories' of TCAS, but at sufficient range to give "two or three minutes" warning rather than the 20s or so of TCAS.

He says: "The European directive for TCAS equipage means that we will not have had sufficient time to prove out some of the ADS-B functions by then. So we would expect to see at least the international [CAA] fleet equipped with TCAS. Although we would prefer not to have to do that."