Ageing Commuters a Potential Source of Long Term Concern

Regardless of whether or not the author of the submission made a mistake in the name of the aircraft in question, it is well known that there are potential problems with the aircraft at the lower end of the commuter airline fleet, due to their age, both in terms of design standard and actual accumulated flying hours. This is not to say that the commuter fleet is inherently unsafe, despite the sensational headlines. Far from it. But it does mean that increasingly expensive effort is needed on the part of both maintenance staff and regulatory authorities, to ensure that the aircraft stay safe, a point also made publicly quite recently by Bob Scott, the CAA airworthiness manager.

The potential problem was very succinctly described by Alan Emmerson, the CAA Manager Maintenance and Durability at the CAA Ageing Aircraft Conference held in Canberra in August 1992 as follows:

“The risks associated with old aeroplanes arise in the main from the difficulty of obtaining support from the manufacturer and other skilled people, and from a general loss of reliability caused by wear and other deterioration.”

Mr Emmerson explained that this loss of reliability took two forms: the visible “self-evident, and hazardous rather than catastrophic” problems of age, and the “insidious and potentially catastrophic” problems of structural fatigue. The former problem is taken care of by good routine maintenance, but the latter is not, and it was this type of problem presumably referred to in the individual submission.

When this type of problem is known to exist, it is preferably managed by establishing an inspection routine which gives an acceptable probability of finding and repairing cracks before they become dangerous. In some aircraft such a procedure is not possible, either because the critical areas are not accessible for inspection or because any cracks are already unsafe by the time they are visible. In this case, the item is given a mandatory retirement life. Typical retirement lives for wing main spar lower caps are shown in our table. The key to success in this system of risk management is anticipating the problem before it is found by accident.

Operators at the lower end of the regional airline market face a Catch 22 situation. Generally, the less profitable the route, the less expensive the aircraft must be to make the route pay, and this inevitably leads to the retention in service of progressively older aircraft. However, while older aircraft are generally cheaper to acquire, they require progressively more effort to maintain them in a safe condition. But the less profitable the route, the less money is available for maintenance.

Ultimately, the continued use of such aircraft becomes uneconomic to the point where it is necessary to either replace them with aircraft requiring less maintenance, or cease operations on that route. The backbone of the Australian commuter fleet, the long out of production Piper PA31 and Cessna 400 series aircraft, have already reached this stage in the USA, with very few remaining in revenue service there. This fact creates additional long term difficulties for the Australian aviation industry.

In the restructuring of the CAA, it was decided that money could be saved by generally relying on the world’s leading aviation regulatory authorities, and in particular the US FAA, for the airworthiness control of our fleet, rather than retaining the large engineering staff inherited from the Department of Transport/DCA. This decision was fine as long as the Australian fleet largely equated with the overseas fleets in terms of aircraft types and ages. But the Australian commuter fleet no longer equates with the US fleet, now almost exclusively turbine powered.

Given the current situation in the GA industry, neither Piper nor Cessna can be expected to willingly continue to devote increasing quantities of scarce resources to obsolescent aircraft approaching the end of their working lives. Similarly, the FAA is less likely to retain as close an interest in these aircraft now that they are no longer in revenue service in the USA. In addition, there has probably been a natural diminution of technical expertise related to the older aircraft within the FAA and the manufacturers.

This then begs the question, was it a mistake to cut back so harshly in the airworthiness branch of the CAA in ongoing surveillance terms, and to rely so heavily on overseas regulatory authorities whose priorities may not necessarily reflect Australia’s priorities or needs? While undoubtedly there were some excesses in the past, given the ageing of our commuter fleet, has the airworthiness surveillance capability of the CAA been cut too far?