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(c) Hidden fault, etc., as mentioned in paint (b) , with the variation that the final breaking of the thread of the central stem occurred immediately before the explOSion as a consequence of the pre—stress exerCised by the check nut, the repeated opening and closing of the cap for refueling, etc. - that is to say, in the course of the practical use of the m1. 750158-13 cap.

01‘ the three hypotheses mentioned above, the one in point c) , regarding the loss in flight of one of the fuel tank caps, is manifestly by far the least probable. Specifically, there is no record that loss in flight of P.N. 75(1138-13 caps has ever occurred in the past (see par. ll.Lt.11). However, Since such a hypotheSis is the only one of the three which is pertinent in so far as the search for the causes of the explosmn of tank No. 7 is concerned, it has nevertheless been taken into conSideration, in relation to the contents of par. 1h.2.5.6.

1h.LL.2.h Explosition set off by bodies striking the_plane's outer surface, whether sucl'Tbodies were extraneous to the plane or were parts of the plane wlfich had become detached from it.

The wreckage of the plane showed no trace of such an eventuality; in particular, all the propellers were found an the ground, together With the engines they belonged With (see par. 11.2.2.2).

111.b.2.5 Explosion set off by explOSive deVices as the result of sabotage

A meticulous examination of the various pieces of wreckage and the results of additional inquiries failed to disclose any eVidence of such a pOSSibility.

The presence of the roll of paper mentioned in par. 11.3.5 in a field together With other pieces of wreckage, in View of

[1] The reenlts of the investigations mentioned in para. 11.3.5 and 11.h.lh;

[2] The fact that, after the loss of the right Wing and the tail asembly, the fuselage Was still a closed body;

[3] The fact that the plane's cargo was found among the main piece of the wreckage (fuselage-left Wing),

has been cons1dered fortuitous; at any rate, even if the roll of paper had been on board the plane, the chemical analyses mentioned in pars. 11.3.5 and ll.h.15 exclude the possibility of its having characteristics such as would set off explosions or start fires.

1h.h.2.6 Egilosmns set off by atmospheric electric discharges

In as much as