Restoration work is taking long than expected on a B-29 Superfortress bomber last used during the Korean War.

The Wichita Eagle reports the giant bomber, dubbed “Doc,” is expected to make its first flight in the spring. It has been undergoing restoration in Wichita for more than a decade after being rescued from the California desert. Volunteers had expected it would fly by the end of 2014.

Restoration project program manager Jim Murphy says the biggest holdup was delays putting in the fuel system. Now weather is a factor because the outside temperature must be above 50 degrees to warm the oil enough to lubricate the engines properly for taxi testing and flight.

The newspaper reports “Doc” will be one of only two restored B-29s now in flying condition.