Stress corrosion cracking was the reason when the undercarriage of a fully loaded and fuelled aircraft broke down prior to take-off, ascertains technical analysis performed by FORCE Technology.

This failure could have become fatal. Fortunately, it did not come to that for the 182 passengers and crew on board the Boeing aircraft that summer night in 2001.

The aircraft was boarding passengers, it was refuelled and fully loaded with luggage, when a truck beam in the undercarriage collapsed, leaving the aircraft supported on the destroyed remains only. No persons were injured, but the situation might have been another, had the failure occurred during landing.

”The Accident Investigation Board Denmark conducts investigations to prevent failures of the same nature. Since we do not dispose of specialist or expert competences in all fields and we do not hold the necessary equipment for performing such specialised tasks, it is very important to know which of our business partners to consult for such competences.

FORCE Technology performed the technical analyses in this case, as they are a competent business partner, who also does not have to question their powers to act in regard to other parties”, says manager of the civil aviation unit with the Accident Investigation Board Denmark, Martin Puggaard.

Identifying failures

”When we initiated the analysis of the unfortunate truck beam in the aircraft’s undercarriage it was quickly obvious that this was a case of stress corrosion cracking, which was also confirmed by thorough scanning and micro structure examinations of the metal.

Subsequently, it was established the surface treatment on the inner side of the pipe had not been performed correctly according to the service manuals from the aircraft manufacturer, which had led to corrosion of the truck beam”, explains FORCE Technology specialist, Hans Peter Nielsen.

Unprovoked events, such as the one occurring on the Boeing aircraft often cause both anxiety and concern with the various actors in the aviation business. Speculations are whether this was an isolated incident or whether it has a more general nature and will recur. Thus it is essential to rapidly identify the failure and provide clarity as to the whole chain of events, so that necessary steps are taken to prevent recurrence.

Clarification

”With FORCE Technology’s report and their conclusion The Accident Investigation Board Denmark could contact the authorities in Denmark and the manufacturing company and point out the reason for the failure. It turned out that there had been two prior similar events, which in turn convinced the manufacturer of changing the outlined maintenance procedures.

Furthermore, an audit was performed on the maintenance facility that had serviced and repaired the component. It was ascertained that the maintenance regulations had not been observed, and the component had not received the correct surface treatment”, says Martin Puggaard.