Lockheed Martin and Boeing are assessing the impact of a heat-treatment anomaly affecting titanium structure in the aft fuselage of the F-22 fighter, but the US Air Force says initial evaluations show no safety of flight issue. No flight restrictions have been imposed, and production and deliveries continue. The anomaly affects the forward booms – large electron beam-welded titanium boxes that support the horizontal and vertical tails. Assessment of the impact, if any, on aircraft service life is under way, but the USAF does not anticipate a need for redesign or retrofit. Boeing builds the aft fuselage, and up to 90 F-22s through production Lot 5 could be affected.