Airspace Management

CASA is also working on a partial ‘user pays’ budget and relies heavily on industry to lobby for what they want. But CASA says industry must be mindful of its limited staff and resources when making their submissions. CASA’s Mike Smith pointed to the example of the removal of the DME-A system. According to Smith, during the time from 1991 when the decision was made to switch off the DMEs until now, industry said little or nothing about a replacement system. But now, just months before ‘D’ day, everybody’s jumping up and down asking what is CASA doing about it.

One of the working groups within GIT is tasked to look at the DME substitution question. At present, operators are making a list of airports not equipped with DME (or won’t be after December 7) and prioritising them in terms of the requirement for an instrument letdown procedure. Implementing a DME arrival could be a simple matter of overlaying an existing DME/NDB or VOR procedure or, as complex as promulgating a brand new stand alone GPS approach. This would involve extensive surveying, site evaluation and flight testing – to say nothing of the time and paperwork involved.

There is the potential, for example, to create a DME arrival, aligned with the runway, effectively looking like an ILS approach to decision height. Instead of starting an approach from overhead the airport, an approach can be designed to start at a point, say 20 kilometres from the end of the runway on the extended centreline. This technique has been successfully demonstrated in Fiji where the cost of installing ground based navaids can’t be justified. However, this is very much a local procedure and only applies to aircraft and operators who are locally approved.

GIT appreciates that the problems of certifying GPS procedures are widespread and complex. At present, the GPS system does not have the integrity and availability necessary to upgrade the aid above its present status as a supplementary IFR en route navigation aid. Another issue is the legal ramifications of approving a system which has the potential of causing huge damages claims should an accident result from the failure of a system for which CASA is responsible. There’s also the issues of having a system which is internationally recognised under ICAO. There needs to be a huge degree of inter-operability between different brands of equipment and flight crew licensing and training requirements need to be discussed, as does implementing an effective NOTAM system for GPS.

82 Australian Aviation September 1995

These problems can be resolved over time, however, a great deal of work is being directed towards the pilot/machine factors in applying the new technology in the cockpit. Currently the workload required to input the relevant information for an instrument approach into a GPS unit involves total pilot concentration. Compared to the present ‘tune to the aid, identify and fly the approach’ concept, there are now many key strokes required to perform a non-precision approach using GPS equipment. In a single pilot, pea-soup situation, where the workload is already demanding, pilots will need to be very familiar with the equipment and procedures. This leads to another important issue revealed at the seminar – human factors and attitudes.

There seemed to be a number of ‘VFR by day’ pilots who came to the meeting emotionally charged with their list of questions about why they can’t use their GPS for this reason or for that. This technology is not intended for VFR navigation, it is the ultimate, sophisticated IFR en route and approach aid of the future. The US FAA has recently approved GPS as a sole means aid for oceanic en route navigation (refer article elsewhere this issue). Sure, the small hand held GPS receivers have their place, and should be used by pilots who have a full understanding of the system’s capabilities as well as its limitations.

At the end of the seminar in Brisbane, it was coupons evident that some pilots were confused by the definitions associated with GPS; integrity, availability and accuracy.

One pilot said GPS was wonderful, it worked for him, so why can’t we all use it? He claimed, “whenever I flew this particular track, I always went over the same tree at the same place every time.” At least he looked out the cockpit at some stage of the flight, even if it was only to confirm his faith in GPS – frightening. An instrument rated pilot, drew on his IFR training and precisely quoted the tolerances of DME equipment. He went on to say, “GPS is more accurate than DME so, why can’t we use GPS instead?” Both pilots had missed the point. No one has ever said GPS was not accurate. CASA has no real problem with accuracy, and soon, with some form of augmentation, the equipment will be approved for non-precision approach procedures.

Another member of the audience used not one, but two GPS units when he went fishing. Sometimes he got two different readings at the same position. This highlighted the integrity and availability problems and the necessity for approved equipment and procedures for aviation.

Ian Mallett from ASA, who heads GIT, related a GPS ‘blind faith’ accident overseas involving a pilot flying IMC by GPS to the initial fix of an instrument approach he was to carry out. Air traffic controllers who were monitoring the aircraft by radar told the pilot he was off course and heading for a range of mountains. The pilot responded by saying his GPS was pointing the right way and there must be something wrong with their radar. The aircraft flew into the side of the mountain at precisely the point where he had programmed the GPS to fly him. The GPS unit survived the crash for investigators to determine this.

There is little doubt, that by adopting an intelligent phased approach to GPS implementation, Australia will no longer require conventional ground based aids. This will ultimately lead to improved efficiencies and significant savings for the aviation industry. A lot will be said in these pages as more GNSS technology becomes available to aviation.