Sometime after midnight on 14 February 1950, a Convair B-36B, United States Air Force Serial Number 44-92075 assigned to the US 7th Bombardment Wing, Heavy at Carswell Air Force Base in Texas, crashed in northwestern British Columbia on Mount Kologet after jettisoning a Mark 4 nuclear bomb. This was the first such nuclear weapon loss in history. The B-36B had been en route from Eielson Air Force Base near Fairbanks, Alaska to Carswell AFB, more than 3,000 miles southeast, on a mission that included a simulated nuclear attack on San Francisco. Incident Convair B-36B 44-92075 was flying on a simulated nuclear strike combat mission against the Soviet Union. The B-36 took off on 13 February 1950 from Eielson AFB with a regular crew of 15 plus a Weaponeer and a Bomb Commander. The plan for the 24-hour flight was to fly over the North Pacific, due west of the Alaska panhandle and British Columbia, then head inland over Washington state and Montana. Here the B-36 would climb to for a simulated bomb run to southern California and then San Francisco, it would continue its non-stop flight to Fort Worth, Texas. The flight plan did not include any penetration of Canadian airspace. The aircraft carried a Mark 4 atomic bomb, containing a substantial quantity of natural uranium and of conventional explosives. According to the USAF, the bomb did not contain the plutonium core necessary for a nuclear detonation. Cold weather ( on the ground at Eielson AFB) adversely affected the aircraft involved in this exercise, and some minor difficulties with 44-92075 were noted before takeoff. Seven hours into the flight, three of the six piston engines began shooting flames and were shut down, and the other three piston engines proved incapable of delivering full power. The subsequent investigation blamed ice buildup in the carburetor air intakes. The crew decided to abandon the aircraft because it could not stay aloft with three engines out of commission while carrying a heavy payload. The atomic bomb was jettisoned and detonated in mid-air, resulting in a large conventional explosion over the Inside Passage. The USAF later stated that the fake practice core on board the aircraft was inserted into the weapon before it was dropped. The aircraft had been in constant radio contact with Strategic Air Command headquarters at Offutt AFB, Nebraska, and within minutes of the bailout the Royal Canadian Air Force launched Operation