The early Heralds had a serious design flaw, the preformed belly skins below the chines had longitudinal top hat stringers fitted, Handley Page had used a form of spot welding to attach the stringers, this process removed the protective surface of the materials and resulted in the rapid process of corrosion in the structure.
Following the fatal crash of CF-NAF, HP reduced the max diff to either 3 psi for aircraft less than six months old, to 2 psi for aircraft between six months and one year old, and zero for aircraft over a year old.
The aircraft were recalled and modified skins were fitted, the new structure was of conventional design, with the top hat stringers attached with three thirty two mush head solid rivets, the skins and stringers being treated with heat cured epoxy resign prior to assembly, and faying surfaces sealed with prc sealant.
To prevent corrosion in service, a system of fibre wicks was fitted, running laterally from chine to chine, with small pellets of strontium chromate fitted, the idea being that moisture would cause the chromate to leach out to protect the structure.
A further problem arose later, with the last dozen or so aircraft converted to cargo aircraft, the requirement for a class E freight compartment meant that all ventilating air had to be ducted to the cockpit and not into the cabin, together with the removal of all sound proofing/insulation caused condensation, this on low utilisation aircraft that were parked up for long periods each day.
The strontium chromate pellets and wicks were eventually removed due to heath and safety and lack of spares, in the final few years corrosion was kept at bay by use of dewatering fluids, a regime of through cleaning and boroscope inspections of the internal structures in the top hat stringers and replacement of skins and structure that showed signs of corrosion.