Nearly one-quarter of the Navy's fleet of P-3C Orion surveillance aircraft were grounded due to concerns about the aging aircrafts' structures. The affected aircraft (39 out of 161 Orions in service) may be down for as long as two years for repairs. According to a Navy spokesman, “Program officials determined that these aircraft are beyond known structural limits on the lower section of the P-3 wing." The Navy began analyzing potential issues with the 1960s-vintage turboprops in December 2004, to anticipate potential risks. Modifications and repairs to the affected planes are expected to take between 18-24 months. Originally developed as a long-legged maritime patrol aircraft, in recent years Orions have also seen service over Iraq and Afghanistan. The Orion fleet is scheduled to be replaced by 108 Boeing 737-based P-8As starting in 2013, though the Navy plans to continue flying Orions until 2019. Lockheed Martin, the manufacturer of the P-3, said its full resources are available to the Navy to rectify the matter.