Douglas DC-7B N8210 took off from Santa Monica at 10:15 for a local functional test flight. At 10:50 a US Air Force Northrop F-89D-40-NO Scorpion (52-1870) took off from Palmdale, also on a functional test flight following overhaul. Purpose of the flight was to check the radar fire control systems of both all-weather interceptors. Both aircraft were performing their tests at an altitude of 25000 feet, over a published local flying zone (bounded by San Diego, Santa Barbara, Bakersfield and El Centro). An almost head-on mid-air collision occurred and part of the DC-7’s left wing was sheared off. The F-89 crashed in flames in the mountains; one of the two crew ejected safely. The DC-7 crashed onto a schoolyard. At the time of the collision the DC-7 was flying at FL250 and at about 330 knots true airspeed to check carburetor operation at maximum cruise power. The F-89 was turning left from a 135deg heading to 45deg heading using a 30deg bank for a simulated intercept. PROBABLE CAUSE: “The high rate of near head-on closure at high altitude, which together with physiological limitations, resulted in a minimum avoidance opportunity during which the pilots didn’t see each other’s aircraft.”