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flight, the plane was in normal condition as regards care and maintenance and structural soundness.
lh.h.l.1 Breakdown because of metal fatigue
The possibility of a collapse of the Wing structure as the result of [metal] fatigue appears unlikely for the following reasons:
(a) No evidence of breakage from this cause was found in the wreckage;
(b) The reSistance of the main structures to fatigue is peeitively evidenced by the results of the speCific laboratory tests made in due time by the Lockheed 00., and by the results of the practical use of the L.16L;9-A planes. In fact, of the 29 planes of this type in service on TWA routes, 19 have had a total number of flight hours greater (by as much as 1,000 hours in some caSes) than those flown by plane N. 7313-0, without showmg any signs of fatigue.
(c) The Wing structure meets the well-known Fail Safe (C.A.R. h b-270) requirements; therefore, even in the case of breakdown of a structural element, no collapse of the entire Wing structure should have occurred.
114.1L.l.2 Breakdown as the result of excessure maneuver stress or offigust
Under the conditions of weight and peeition of the plane's center [of granty] at the time of the accident and in the
presumed climbing trim, with the speed of 170 knots or less indicated on the flight path, neither intentional maneuver nor positive, or negative, gust of any intensity could have caused the breakdown of the wing because, before the forces necessary to cause the collapse of the structure had appeared, the wing would have gone into a stall.
At speeds higher than that indicated above, that is, in case the plane had gone into faster flight trims than its climbing trim, the Wing could not have broken away except under one
of the following conditions:
(a) Maneuver: Exceeding the pOSitive load factor 14.5 g. This condition appears to be unlikely, becausa the coefficient 11.5 is very high (13% of the prescribed maneuver limit factor) and to reach it would have required a sharp maneuver at a very high speed, such as after a prolonged dive, which does not seem likely to have happened in View of the suddenness of the accident, but above all, because the breaking of the Wing should have ocourred in the outer part between station 525 and the Wing tip and not in the inner part, as actually happened.
