Kieran Daly/LONDON

A KEY ELEMENT of the USA's airport-capacity enhancement programme is being held up following unexpected difficulties in using it operationally.

The precision runway monitor (PRM), has an electronically scanned (E-scan) radar, with a high update rate, to permit independent approaches to closely spaced, parallel runways.

Following trials at Raleigh-Durham Airport, North Carolina, the US Federal Aviation Administration has approved such approaches at runways as close as 3,400ft (1,050m), rather than the 4,300ft previously required.

It needs to get down to at least 3,000ft for use at major airports, including New York Kennedy International, where the biggest capacity gains are achievable.

The FAA has a $34 million contract with AlliedSignal Aerospace for an initial five PRMs and a virtually identical system is being bought for Kingsford-Smith Airport in Sydney, Australia.

Although the development system at Raleigh-Durham was formally commissioned following the trial work, it has emerged that the US Air Line Pilots Association (ALPA) and the Allied Pilots Association advised its members on safety grounds not to use it and, in practical terms, it has never been operationally used.

New PRM simulation work, at the Mitre Research Laboratory, has confirmed that the system is unacceptable at 3,000ft runway spacing.

ALPA's primary concern is that a blocked transmission - when a controller fails to communicate with a pilot because the pilot transmits simultaneously - could lead to a collision.

The phenomenon is critical for the PRM because the controller may have minimal time to tell a pilot to go around if one aircraft approaches another.

ALPA's Tom Kreamer, who is also North Atlantic regional vice-president of the International Federation of Airline Pilots Associations, says: "The PRM as a concept is very good and very viable, but ALPA does not think it is ready to be used in the USA at this time. For a long time, no one would admit that we had a problem with blocking. The pilots should never be put in this position."

FAA programme manager for acquisitions, Byram Johnson, says that the agency now intends to test the UK-produced Contran communications anti-blocking system. If the plan goes ahead, the FAA would buy perhaps four examples of the ground element from Contran.

Johnson and PRM programme manager Gene Wong say, however, that the blocking issue is secondary to a need for better pilot and controller training.

Johnson says: "If you look at the time it takes for the aircraft to respond [when there is a conflict], it takes the controller perhaps 3s and, in the worst case we observed, 45s for a pilot to react - although that involved a number of worst factors."

Wong explains that the problem is mostly with glass-cockpit aircraft where auto-pilot-coupled approaches are used.

Source: Flight International