The Inverythan rail accident occurred when a faulty girder collapsed on a single-track railway underbridge between Auchterless and Fyvie. The engine of the freight/passenger train (5 loaded wagons, 4 carriages) crossed safely, but most of the train fell into the gap onto a road below. Cause A simple vertical crack with a freshly fractured surface and old rust marks on the face was easily distinguished to the side of the centre joint, extending from the bottom flange to the top of the girder. This was associated with a casting defect hidden behind a surface skin of sound metal at the thickest part of the section where the flanges met the web. This was described by the accident report as a large honeycomb, or drawhole, which measured 3½ ins (c 90 mm) across at the face, and narrowed to about 1½ ins (c 40 mm). inside , 2⅜ ins (c 60 mm) in extreme depth and 6ins (c 150 mm). in extreme length, extending inwards and downwards ...but not within 1 ½ ins of the outer face of the joint flange. The total capacity of the hole, measured by filling it with water, was 15 ½ cubic inches (about 250 ml) and, as the metal immediately round the hole was not sound, this amount does not measure the actual extent of the flaw. There were other signs of poor foundry practice when the girder had been cast; honeycombing elsewhere, a cold shut (incomplete fusion between different streams of filling metal), and residual stresses in the girder web (as a consequence of which, when sample cores were being drilled for testing, the web (but not the flanges) fractured along the line of holes. Whilst the metal appeared to be of good quality to the naked eye, the tested tensile strength of the metal varied widely from the shaft lowest of ~4.5 tsi (c 70 MPa) (close to the honeycombing) with a mean of 7.5 tsi (c 115 MPa). The accident report says that the girder if sound would have had a breaking strength of 80 tons and concludes that the theoretical strength of the girder was 'above but only just above' the Board of Trade requirement (live load x 6 + dead load x 3) (However this appears inconsistent with the figures quoted by the report for dead weight (21 ton shared between 2 girders) and live load (21 ton shared between