(185d) It All Adds up...the Impact of Cumulative Changes on Safety and Production

On 21^st December 1999 a Cessna 150M aircraft attempted a take-off at Moorabbin General Aviation Airport in Australia. Just after take-off the engine lost all power. The pilot managed a forced landing onto the grass at the end of the runway. On touch down, the engine resumed power. This event saw up to 5000 piston engine aircraft grounded and triggered an investigation from the refinery that manufactured the fuel in the plane. An independent investigation by the Australian Transport Safety Bureau determined a series of cumulative changes in how the fuel was manufactured led to carry over of a corrosion inhibitor, which contaminated the fuel. Cumulative changes are often hard to track, as their consequences may not be readily apparent. This paper will explore the cumulative changes that occurred, and how the application of a new risk assessment technique, Delta HAZOP, may have assisted in uncovering the impacts of the cumulative changes. Delta HAZOP views a system more holistically and looks for the impacts of cumulative changes, to uncover risks that may be missed via the guideword approach.