The Inverythan rail accident occurred when a faulty girder[1] collapsed on a 39 by 15 ft (11.9 by 4.6 m) single-track railway underbridge between Auchterless and Fyvie.

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.

[1]It was considered that the fault could not have been detected by routine inspections, so no blame attached to those responsible for inspecting the bridge, but this conclusion gave the BoT inspector considerable concern: For, if one such girder, which was of sufficient theoretical strength when cast, and which, being in constant use for 25 years, had never shown any signs of weakness or any outward flaw, suddenly breaks down, owing to a defect which must have existed when it was originally made, and laid latent ever since, it is very difficult to know what steps should be taken to guard against the recurrence of a like disaster.

Little further action was taken until the 1891 Norwood Junction rail accident of a first class train which injured 1 businessman because of a cast iron girder fracture from a latent defect.