New safety fears for RAF Nimrods, page 1

You have brought up a matter which I believe demands a much wider awareness.

We live in an era when a couple of aircraft types seem to have gone on for ever and ever, the DC-3 / Dakota and the B-52 (no doubt due to massive over-engineering and intensive maintenance).

We have apparently forgotten that the forces of nature that degrade the strength of materials, such as metal fatigue and corrosion are just that - forces of nature! Yes, to a LIMITED extent, these problems can be overcome (read delayed), but it is inevitable that in the end these forces will prevail.

In the case of the F-15, the US public (and no doubt the decision makers) have been convinced that the airframes can last longer than the period (cycles) for which they were designed - but on what basis? Do current engineers think that the engineers of 30 or 40 years ago were idiots? In contrast to aircraft such as the DC-3, even aircraft designed 40 years ago, were designed to be no stronger (hence heavier) than they needed to be to endure for their planned life cycle. Do current engineers believe that they can alter the laws of nature? Perhaps they do, but if so they are deluding themselves - and the public.

Nothing, repeat NOTHING lasts forever, especially items made from metal, and short of replacing the metal structure of an object, nothing is going to make it last forever!

Of course this situation is not confined to aircraft, evidence the recent bridge collapses (metal fatigue), steam pipe failure/explosion in New York, etc.

The laws of nature require that every metal bridge will have to be replaced after 'x' number of cycles - there is absolutely no other alternative - you cannot make a metal bridge last forever - it is like talking of perpetual motion, while friction exists perpetual motion is IMPOSSIBLE!

This attitude even seems to extend to the automobile. Yes, advances in lubrication have allowed the extension of time between oil changes (TBO in aviation terms), but they have not eliminated them - and they never will. Unfortunately, the importance attached to vehicle servicing by our grandfathers has now been totally lost on this generation. We no longer service to prevent failure - we just throw the item away when its (shorter than it should be - due to lack of servicing) life is over.

If society can afford such waste then, fine, but let's not deceive ourselves into thinking we can make the same item last forever, just because it will last some finite time without servicing, or component replacement.

So it is well to remember that if we build, say, a bridge then we are not only committing to the cost of the bridge and its maintenance, but eventually it's total replacement after a given amount of usage. In the case of underground structures (such as New York's steam pipes) we had better plan, during its design, for the ability to replace parts or all of the structure. Unfortunately (and no doubt catastrophically) designers (and legislators) only plan for the life of the product not for what has to be done to eventually and inevitably replace the item.

Surely, much of the blame for this falls upon the shoulders of politicians (with the tacit approval of the electorate) who will not make the hard decisions to replace systems BEFORE they planned life has expired, but rather to extend the life of the systems (on obviously shaky and optimistic grounds) merely to get re-elected.

An obvious lesson (which I believe will go unheeded) is the case of the F-15 (and the Nimrod), is that you cannot plan or extend the life of a system such as a warplane - and thus its replacement - on a peacetime utilization rate, especially when the lead time to introduction of a replacement system is in the order or 20 years or more. If the F-15 structure cannot be repaired, just how many years will it be before the USAF is back to its capability level before the wings started falling off? Perhaps never!

And this from the 'most powerful' nation on earth. How pitifully weak we humans really are!

The Winged Wombat