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the human equation in the form of the pilot and crew. There is an increasing awareness of the fact that the experience and point of view of operating personnel should be intimately joined with that of the designer from the beginning."

And a leading manufacturer, in a personal communication to the author, wrote, in discussing the contributions made by active airline pilots to the success of the design in question:

"The question of why there was success here and not elsewhere seems to be answered by the timing factor. This program was set up at a very early date in the development thus allowing enough time to thoroughly discuss differences of opinion and reduce them to an objective common denominator."

We wish the thoughts expressed above were more widely practiced within the industry.
In passing, it might be well to note that the Air Line Pilots Association is carrying on an active campaign of familiarization with the problems of design and operation of turbine powered transports in anticipation of their early commercial application, and we would welcome the opportunity to contribute to their safe and efficient development. 

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OPERATIONS

Given an initially sound design, the next and very important step in making it a safe plane to fly is the "debugging" of it under actual operations. Contrary to popular opinion this process does not end with the first few years in service but extends throughout the total operating life. Figure 3, "Accident Rate as a Function of Cumulative Miles Flown", shows this clearly. Though the initial 4 or 5 hundred million miles are probably the most important, the DC-3's long history shows a continuous gradual improvement beyond that point. This initial rapid improvement is also clearly shown by the DC-4 and 6 curves, evidence of the excellent joint efforts of the manufacturer and operators. If their future development parallels that of their predecessor, and if other current transport types are improved at the same high rate as has been shown for these types, we indeed have promise of a marked improvement in the overall accident rate.

Incidentally, in the preparation of this figure it was not meant to slight other types. The aircraft plotted were chosen because their accumulated mileage in domestic scheduled service was sufficiently large to plot a reasonably smooth curve. 

Also pointedly showing the effects of improvements while

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