The Goldsboro nuclear bombs were not "one step away" from detonation, and could not have detonated in a nuclear sense due to several safety factors. The first, and most important, is that the bomb's Ready/Safe Switch could only be rotated to "arm" by the pilot and radar navigator using the Aircraft Monitoring and Control equipment (AMAC). The AMAC used a very specific aircraft voltage and amperage, which could only be supplied by the pilot's T-380 Readiness Switch. The bomb's short life thermal batteries only supply power to bomb components, not the arming and safing system. The aircrew had to perform at least 19 steps to even pre-arm and drop a nuclear bomb, by two physically separate and knowledgeable aircrew members. These devices were also safety wired and sealed to protect against inadvertent activation and tampering.
Second, the bomb had additional safety features against unintentional arming. These included the Trajectory Arm Switch, and X-Unit Rotary Safing Switch. Bomb 2, which impacted near Faro, NC and buried itself into the ground, hit the earth without it's High Voltage Thermal Battery (HVTB) activating. Thus, there were a total of three safety switches (not one) in the bomb to prevent a nuclear detonation. Given the fact that the HVTB did not activate nor supply power to bomb components, a nuclear detonation could not take place.
Finally, a number of components were not activated which were necessary for a nuclear explosion. Looking thorough the declassified arming and fusing sequence shows that many more steps were necessary to place the bomb into a condition necessary for a nuclear detonation. Documentaton obtained through the Freedom of Information Act, including the copies of the original AEC and EOD reports, are available in the book "Broken Arrow, The Declassified History of Nuclear Weapons Accidents" by Michael H. Maggelet and James C. Oskins. It should also be noted that only the bomb's secondary, containing uranium and lithium, was not recovered and poses no detonation hazard.
How close was the bomb to firing? Not at all.
More information about formatting options