The main structural components, spars and beams of the Valiant had been constructed from a zinc/magnesium/copper aluminium alloy designated as DTD683 in the UK. The Valiant had been designed with a 'Safe-Life' strategy; this combination of 'Safe-Life' and DTD683 came to be viewed as a severe mistake. In 1956, a publication within the Journal of the Institute of Metals condemned the material DTD683 as being unstable and capable of catastrophic failure when stressing the airframe close to its design limits. The "Safe-Life" design strategy was dismissed by a Lockheed engineer in a talk given to the Royal Aeronautical Society in 1956, because it did not guarantee safety from catastrophic failure.