It seems strange that, in an industry, which is rightly obsessed with safety, there should be a disagreement between major players over whether particular safety standards should be applied to particular aircraft. It seems even stranger that the disagreement is based not on when a particular airframe was built, but on when the first broadly similar airframe was built.

A derivative airframe designed today can, in effect, be certificated to the standards, which applied when the original was first designed, but a totally new design must conform to the latest regulations. Thus, a 1990s derivative of a 1960s design can reflect 1960s practice, but a 1990s derivative of a 1980s design cannot.

The usual driver for a change in regulations in civil aviation is safety. There are two main sorts of change - those, which are driven by failure; and those which are driven by improved knowledge or practice. Those, which are driven by failure, tend to be retrospective and largely have to be implemented on existing and new designs alike, regardless of cost or convenience. Those, which are driven by improved knowledge or practice, are usually prospective - regarded as non-urgent and to be implemented only as new designs are created.

It is these latter improvements which cause the trouble in the treatment of derivative designs. Knowledge or practice may have been improved since the original design was created, and a totally new design would be expected to incorporate those advances.

In the absence of failures in an earlier design, however, it can be difficult (or even impossible) to justify on economic grounds the incorporation of those advances in derivatives of that design. What might be seen as economic sense to the builder of that design (and to its customer) will not, however, to a manufacturer, which does not have the option of offering a derivative.

If the latter manufacturer wants to break into a new market sector, it must design its new aircraft to the latest specification and standards. Such a totally new design could involve penalties for both constructor and customer. The constructor has to make something to a higher (and almost inevitably, more expensive) standard; the customer might have to accept burdens such as a weight penalty, or bigger spaces around exits, as well as that of extra cost. Either way, a newer, supposedly more efficient, basic design can end up being uncompetitive in the short term with a new derivative.

The suggestion by some Airbus managers that they should be allowed to re-certificate the A320 to the same standard as that being applied to the latest derivatives of the Boeing 737 is not, as they are well aware, a realistic solution. If an improvement in standards was worth making in the first place, it is worth keeping, and to effectively downgrade a standard for commercial reasons is a denial of the whole process. Airbus' unhappiness is understandable.

Equally inadequate is the grayness of definition, which fails to draw hard lines on the extent to which a new design can be considered to be a derivative. In Boeing's eyes, a new wing does not make the new 737 a new design: in some regulators' eyes, it does.

The only possible way out of what appears to be an intractable problem would appear to be not a change in the definition of "grandfather" rights as they apply to derivatives, but a change in their application. Changing the whole design of an existing structure to accommodate a new performance standard is one thing: changing what is an acceptable number of seats is another. The one could be seen as imposing an unacceptable burden on the manufacturer through having to make a massive investment in new engineering on an old model; the other could be seen as merely affecting an artificially produced marketing advantage.

Getting agreement between manufacturers over what would be an acceptable formula for applying grandfather rights (or "dispensations" as they should rightly be called) might be difficult. Getting the world's significant airworthiness authorities to reach agreement on that issue should be easier, as they should be independent and non-partisan. Either way, this is not a subject on which the industry should be indulging in disagreements, but one on which it should be producing solutions.

Source: Flight International