For our methodology, we applied the practices for the procurement of military products that are normally used in the United States. Their Department of Defense uses 30 years as its base period. This corresponds to the lifespan of an F-18, according to the manufacturer's estimated lifespan of 8,000 flying hours. This number is then divided by the average number of hours of use per year. So the aircraft's normal and expected lifespan is set at 30 years in the industry, using a number of measures.
On May 3rd, 2012. See this statement in context.