On January 27, Missile 4C experienced a complete Mod III GE guidance system failure at T+80 seconds.

The propellant utilization system operated fuel rich, resulting in low sustainer thrust following BECO, and LOX depletion caused simultaneous sustainer/vernier cutoff 5 seconds earlier than the planned SECO.

Overall performance of 11C was quite good, the sustainer HS valve malfunctioned and resulted in reduced LOX flow to the engine, this resulted in low sustainer thrust and complete fuel depletion by SECO, and it was suspected that a leak in a LOX duct had affected the HS valve.

[7] One of the more significant upgrades to the Atlas C was the addition of motion detectors in the gyroscope package to ensure proper operation.

This was implemented after the first B-series Atlas had failed in flight due to launch crews neglecting to power on the gyroscopes and would soon become a standard part of all ballistic missile guidance systems.

However, the launch was postponed due to repeated technical problems and the vehicle put in storage to free up LC-12 for Missiles 8C and 11C.

The postflight findings from Atlas 5C necessitated modifications to the fuel staging disconnect valve; these were performed in late July.

Investigators concluded that the disaster was due to the above-mentioned configuration change on the Atlas C, in addition to several weight-saving modifications unique to Missile 9C.

When the Atlas was assembled at Convair, workmen attached a helium vent line to a port near the bottom of the RP-1 tank, below the anti-slosh baffles.

The reason for the LOX ducting rupturing was not clear, but likely the sudden pressure change from the engine shutdown or the sustainer turbopump blades rubbing against the pump casing.

The accident was ultimately ruled to be the result of poor engineering judgement in attaching the vernier helium vent line to the bottom of the RP-1 tank.

This was not the first occurrence of the failure mode; Missile 6C had exploded on the test stand at Sycamore Canyon the previous March due to the vernier start tanks being connected incorrectly.

The sustainer gas generator had suffered a LOX-rich shutdown and had extensive heat damage; the turbine blades were melted away.

Final explosion of the missile was believed to be loss of tank pressure resulting in collapse of the intermediate bulkhead and all of the LOX and RP-1 mixing and turning to gel, which then exploded with the force of 20,000 pounds of TNT.