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CliffS wrote:

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emc wrote:

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iirc, the average flight time for currently active 747's is about 100,000 flight hours. Yes, commercial aircraft are used as close to 24/7 as is possible (sometimes too close; Southwest Airlines apparently neglected their maintenance to keep aircraft flying). I remember reading a story a few years ago (it was in a trade publication, but not AvWeek) of a 727 that accumulated something like 700 flight hours in a month. It was exceptional; I suspect that average for the aviation industry is about 450 to 500 hours per month, which is probably more than the average peacetime annual flight time of most US military aircraft.

A airliner in revenue service would probably use up 28,000 hours of airframe life in less than 5 or 6 years.

In Australia, Ansett Airlines went broke through trying to support a fleet of superannuated B-767s as though they were new. As airframes age, the maintenance periods come closer together. Ansett found they couldn't afford the downtime with their tight schedules - for either the 767-200s or their 737-300s. The planes were just falling apart, and passenger confidence was severely eroded. The Civil Aviation Safety Authority grounded several aircraft after maintenance-related incidents, and Ansett could no longer function. Of course, a big fuel price rise also played a part in this sorry tale. Even QANTAS were hanging on by their fingernails about 7 years ago.

Cheers,
Cliff

Well, a bunch of US airlines just got caught in major maintenance screw-ups. Part is, no doubt, due to years of lax oversight by the FAA (much as I dislike Bush & Co, I think the problem goes back to the Carter Administration), and part is doubtless due to managers who are less concerned with safety than the bottom line.

Michael ODonnell wrote:

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The cycles versus flight hours also explains why short-haul aircraft are heavier than longer ranged aircraft (for a given size). The short-haul aicraft have to take into account the more frequent pressurisation cycles, plus more take-off and landing cycles, and will therefore have a stronger (and heavier) structure. There is a lot that goes into the design of an aircraft, you have to match the design to the requirements of the role, not the other way around. While there may seem to be similarities between passenger airliners and bombers (large size, long range, heavy payload), there are so many differences that there has been (to date) no real attempts to use civil airliners as heavy bombers.

iirc, there were a couple of attempts in the 1930's, which usually failed miserably