The 1961 Goldsboro B-52 crash was an aviation accident that occurred near Goldsboro, North Carolina, United States, on 24January 1961. A Boeing B-52 Stratofortress carrying two 3.8-megaton Mark39 nuclear bombs broke up in mid-air, dropping its nuclear payload in the process. Five crewmen successfully ejected or bailed out of the aircraft and landed safely; another ejected, but did not survive the landing, and two of them were killed in the crash.
The accident is one of the most famous "Broken Arrow" nuclear accidents of the Cold War. Both of the weapons began their firing sequences upon separation from the aircraft, despite safeguards meant to prevent that from occurring. One of its nuclear bombs was judged by nuclear weapons engineers at the time to have been only one safety switch away from detonation, and that it was "credible" to imagine conditions under which it could have detonated. The other bomb did not get as far into its firing sequence, but became deeply embedded in a muddy field, and one of its major weapons components (the thermonuclear "secondary" stage) was regarded as irrecoverably lost after an extensive, failed effort to recover it.
Accident
The aircraft, a B-52G, was based at Seymour Johnson Air Force Base in Goldsboro, and part of the Strategic Air Command's airborne alert mission known as "Cover All" (a predecessor to Operation Chrome Dome), which involved a continuous flow of staggered, nuclear-armed bombers on a "ladder" route into the Canadian Arctic and back.. "Accident #3" on page 36 of the report is clearly (despite redactions) the Goldsboro accident, and associates it with a "Project Coverall operation."
Around midnight on 23–24January 1961, the bomber had a rendezvous with a tanker for aerial refueling. During the hook-up, the tanker crew advised the B-52 aircraft commander, Major Walter Scott Tulloch, that his B-52 had a fuel leak in the right wing. The refueling was aborted, and ground control was notified of the problem. The B-52 was directed to assume a holding pattern off the coast until the majority of fuel was consumed. However, when it reached its assigned position, the pilot reported that the leak had worsened and that of fuel had been lost in three minutes. The aircraft was immediately directed to return and land at Seymour Johnson Air Force Base.
As the aircraft descended through on its approach to the airfield, the pilots were no longer able to keep it in stable descent, and "lost all control as the B-52 went into a gyration best described as a spin." The pilot in command ordered the crew to abandon the aircraft, which they did at . Five men landed safely after ejecting or bailing out through a hatch, one did not survive his parachute landing, and two died in the crash. The third pilot of the bomber, Lt. Adam Mattocks, is the only person known to have successfully bailed out of the top hatch of a B-52 without an ejection seat. The crew's final view of the aircraft was in an intact state with its payload of two Mark39 thermonuclear bombs still on board, each with yields of 3.8 megatons. Sometime between the crew ejecting and the aircraft crashing, the two bombs separated from the aircraft.
The unmanned aircraft broke up in the air shortly after the crew ejected. Witnesses reported seeing two flashes of red light, suggesting that fuel explosions contributed to the breakup of the plane. At on January24, the remaining pieces of the B-52 impacted with the ground. The aircraft wreckage covered a area of tobacco and cotton farmland at Faro, about north of Goldsboro. The arrangement of the aircraft pieces suggested that several pieces of the B-52 were upside down when they struck the ground.
Explosive ordnance disposal (EOD) teams from Seymour Johnson and other bases arrived on the scene quickly, disarming the one bomb that was easily accessible. Representatives from the Albuquerque Operations Office of the U.S. Atomic Energy Commission were alerted to the accident on the morning of January24. A team of scientists and engineers from the AEC, Sandia National Laboratories, and Los Alamos National Laboratory assembled at Kirtland Air Force Base in New Mexico. They were joined by representatives from the Department of Defense Nuclear Safety Research Directorate. They flew to Seymour Johnson AFB on a C-47 cargo plane, arriving at approximately on the night of January24.
Weapons Mark 39 Mod 2 nuclear bombs
The two bombs involved in the Goldsboro accident were Mark39 Mod2 thermonuclear weapons with a maximum predicted yield of 3.8megatons of TNT equivalent. It was a multi-stage thermonuclear weapon with a "primary" and a "secondary" stage. In such weapons, the "primary" is a mostly-fission driven stage whose energy is used to compress the "secondary," which initiates further fission reactions, nuclear fusion reactions, and the neutrons generated by the fusion stage can in turn generate more fission reactions.
In the case of the Mark39 Mod2, the "primary" was also boosted, meaning that at the moment of detonation a gaseous mix of deuterium and tritium was injected into its core, which would generate fusion reactions at the moment of detonation, producing neutrons that would increase the efficiency of the "primary". The pit of the primary was entirely composed of enriched uranium ("all-oralloy"), with no plutonium, and had a sealed-pit, meaning that it was fully-assembled at all times. The "secondary" also contained enriched uranium in its "sparkplug." The Mark39 Mod2 warhead was itself enclosed in a gravity bomb casing which had a compartment containing a drogue parachute that both allowed the aircraft dropping it to move to a safe distance, and allowed it to be detonated on the surface by a contact fuze without risk of the weapon breaking on contact with the ground. The weight of the assembled bomb was between .
Immediately after the Goldsboro accident, technicians from Sandia National Laboratories, the national laboratory which had the primary responsibility of nuclear warhead safety engineering, subjected the recovered weapons to careful analysis to determine how close they were to a possible nuclear detonation. Various accounts of their conclusions have circulated over the years, with some emphasizing the closeness of the detonation, and some emphasizing the success of the various safety features of the nuclear warheads. To make sense of their analysis and the controversies, it is first necessary to understand what the normal firing sequence of a Mark39 Mod2 used in combat conditions would be.
The Mark39 bombs would be suspended in the two bomb bays of the B-52 plane carrying it, one in front of the other. "Arming rods" were extended out of each weapon, and held in place with "safing pins." Prior to normal use, the "safing pins" would need to be pulled out of the bomb horizontally, which could be done by the crew in the cockpit by means of a lanyard that was connected to them. Additionally, prior to dropping the bomb, the pilot would need to operate a switch inside the cockpit (the T-380 Readiness Switch), which would enable the navigator to power-on and "arm" another switch (the T-249 Aircraft Monitor and Control Unit). The latter would operate the MC-772 Arm/Safe Switch inside the Mark39 bomb itself. The Arm/Safe Switch was a low-voltage, solenoid-operated electro-mechanical switch that was kept in the "Safe" position until a deliberate choice was made to cause a nuclear detonation, but could be switched from "Safe" to "Arm" by a 28-volt electrical signal.: "And that one safety device was the pre-arming switch which was operated normally by a 28-volt signal." The Mark39 Mod2 could only be detonated as a "contact" burst (and not an airburst). The bomb bay had a solenoid-operated lock system which would deploy the parachute automatically upon release if operated, as opposed to a free-fall release.
Once the bomb cleared the bomb bay and the arming rods were retracted, they would trigger the MC-845 Bisch generator they were connected to. This was a single-pulse generator that began the overall firing sequence. The Bisch generator would send an initiation signal to the MC-640 low-voltage thermal battery pack, as well as the MC-543 Timer. The timer would begin to count down. The retraction of the arming rods would also close valves sealing a reference chamber in the MC-832 Differential Pressure Switch, a barometric fuze for detecting the bomb's altitude.
After the weapon had fallen a required vertical distance, the differential pressure switch would close contacts which passed battery current through the MC-772 Arm/Safe Switch and from there to the MC-788 High Voltage Safing System, which is armed by continual current being applied to it. Upon receiving this current, the MC-788 would then connect the (not yet-charged) high-voltage thermal battery to the X-Unit, the electrical device that provides a high voltage signal to the detonators used in the "primary" stage of the weapon. After the timing circuit completed its countdown of 42 seconds, it would then deliver initiation power to the MC-641 High Voltage Thermal Battery pack. This would begin to generate its full voltage of 2,500volts within one to two seconds, which would be applied directly to the trigger circuit and, through the MC-788 High Voltage Safing System, to the capacitor bank of the X-Unit. Once the bomb impacted the ground, a crush switch on the nose of the bomb (the MC-787 Trigger Circuit) would be closed and trigger the X-Unit to discharge its capacitors and initiate the high-explosive system in the "primary" stage of the weapon.
At some point in the above sequence, not indicated in declassified documents (possibly because of its classified nature), "squibs" on the Los Alamos Laboratory 1A Valve Mechanism would fire and cause the gas from the boost reservoir to be injected into the "primary" of the bomb.
By the time of the Goldsboro accident, the MC-772 Arm/Safe switch had been replaced in some Mark39 Mod2 units with another switch, the MC-1288 Arm/Safe switch, which also restricted the charging of the low-voltage thermal battery if the switch was in the "Safe" position. This was done to ensure additional safety for the weapons, and would remove the need for safing pins in the pullout rods. This modification (designated as Alt197) had been approved in January 1960, but had not been performed on either of the bombs involved in the Goldsboro accident.
For a parachute delivery, the Mark39 would need to be released between and above the target. For a free-fall delivery, it would need to be released at least above the target, or else it would hit the ground prior to the timer circuit completing its countdown and the X-Unit being charged.
The two Mark39 Mod2 nuclear bombs involved in the Goldsboro crash had distinctly different outcomes. Official reports identified them as weapon no.1 (or bomb no.1) and weapon no.2 (or bomb no.2), with the first's parachute having deployed and the second having crashed into the ground in free-fall without any decrease in its speed. Weapon no.2 was kept in the forward bomb bay of the aircraft, while weapon no.1 was in the aft bomb bay.
Weapon No. 1: Serial No. 434909 (parachute)
Weapon no.1, identified as serial number 434909 (and kept in the aft bomb bay), was flung out of the aircraft at an altitude of around above the ground. It apparently twisted from its rack in a way that caused the "safing pins" on its arming rods to pull out longitudinally and without any sign of damage, despite not having been pulled from the crew compartment. Once it left its rack, the bomb dropped in such a way that its arming rods were pulled out in much the same manner as an intentional drop sequence would be. This caused its MC-845 Bisch generator to be actuated, initiating the MC-640 low-voltage thermal battery pack and the MC-543 timer. The explosive actuators triggered the deployment of the bomb's parachute as in normal functioning.