# Apollo 13 Accident Chronology

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National Aeronautics and Space Administration
Detailed Chronology of Events Surrounding the Apollo 13 Accident
Events from 2.5 minutes before the accident to about 5 minutes after. Times given are in Ground Elapsed Time (G.E.T.), that is, the time elapsed since liftoff of Apollo 13 on April 11, 1970, at 2:13 PM Eastern Standard Time (EST). 55:52:00 G.E.T. is equal to 10:05 PM EST on April 13, 1970.
55:52:31 - Master caution and warning triggered by low hydrogen pressure in tank no. 1
55:52:58 - CapCom (Jack Lousma): "13, we've got one more item for you, when you get a chance. We'd like you to stir up the cryo tanks. In addition, I have shaft and trunnion .....
55:53:06 - Swigert: "Okay."
55:53:07 - CapCom: ".... for looking at Comet Bennett, if you need it."
55:53:12 - Swigert: "Okay. Stand by."
55:53:18 - Oxygen tank No. 1 fans on.
55:53:19 - Oxygen tank No. 2 pressure decreases 8 psi.
55:53:20 - Oxygen tank No. 2 fans turned on.
55:53:20 - Stabilization control system electrical disturbance indicates a power transient.
55:53:21 - Oxygen tank No. 2 pressure decreases 4 psi.
55:53:22.718 - Stabilization control system electrical disturbance indicates a power transient.
55:53:22.757 - 1.2 Volt decrease in ac bus 2 voltage.
55:53:22.772 - 11.1 amp rise in fuel cell 3 current for one sample
55:53:26 - Oxygen tank No. 2 pressure begins rise lasting for 24 seconds.
55:53:38.057 - 11 volt decrease in ac bus 2 voltage for one sample.
55:53:38.085 - Stabilization control system electrical disturbance indicates a power transient.
55:53:41.172 - 22.9 amp rise in fuel cell 3 current for one sample
55:53:41.192 - Stabilization control system electrical disturbance indicates a power transient.
55:54:00 - Oxygen tank No. 2 pressure rise ends at a pressure of 953.8 psia.
55:54:15 - Oxygen tank No. 2 pressure begins to rise.
55:54:30 - Oxygen tank No. 2 quantity drops from full scale for 2 seconds and then reads 75.3 percent.
55:54:31 - Oxygen tank No. 2 temperature begins to rise rapidly.
55:54:43 - Flow rate of oxygen to all three fuel cells begins to decrease.
55:54:45 - Oxygen tank No. 2 pressure reaches maximum value of 1008.3 psia.
55:54:51 - Oxygen tank No. 2 quantity jumps to off-scale high and then begins to drop until the time of telemetry loss, indicating failed sensor.
55:54:52 - Oxygen tank No. 2 temperature sensor reads -151.3 F.
55:54:52.703 - Oxygen tank No. 2 temperature suddenly goes off-scale low, indicating failed sensor.
55:54:52.763 - Last telemetered pressure from oxygen tank No. 2 before telemetry loss is 995.7 psia.
55:54:53.182 - Sudden accelerometer activity on X, Y, Z axes.
55:54:53.220 - Stabilization control system rate changes begin.
55:54:53.323 - Oxygen tank No. 1 pressure drops 4.2 psi.
55:54:53.500 - 2.8 amp rise in total fuel cell current.
55:54:53.542 - X, Y, and Z accelerations in CM indicate 1.17g, 0.65g, and 0.65g.
55:54:53.555 - Master caution and warning triggered by DC main bus B undervoltage. Alarm is turned off in 6 seconds. All indications are that the cryogenic oxygen tank No. 2 lost pressure in this time period and the panel separated.
55:54:54.741 - Nitrogen pressure in fuel cell 1 is off-scale low indicating failed sensor.
55:54:55.350 - Telemetry recovered.
55:54:56 - Service propulsion system engine valve body temperature begins a rise of 1.65 F in 7 seconds. DC main A decreases 0.9 volts to 28.5 volts and DC main bus B 0.9 volts to 29.0 volts. Total fuel cell current is 15 amps higher than the final value before telemetry loss. High current continues for 19 seconds. Oxygen tank No. 2 temperature reads off-scale high after telemetry recovery, probably indicating failed sensors. Oxygen tank No. 2 pressure reads off-scale low following telemetry recovery, indicating a broken supply line, a tank pressure below 19 psi, or a failed sensor. Oxygen tank No. 1 pressure reads 781.9 psia and begins to drop.
55:54:57 - Oxygen tank No. 2 quantity reads off-scale high following telemetry recovery indicating failed sensor.
55:55:01 - Oxygen flow rates to fuel cells 1 and 3 approached zero after decreasing for 7 seconds.
55:55:02 - The surface temperature of the service module oxidizer tank in bay 3 begins a 3.8 F increase in a 15 second period. The service propulsion system helium tank temperature begins a 3.8 F increase in a 32 second period. 55:55:09 - DC main bus A voltage recovers to 29.0 volts, DC main bus B recovers to 28.8.
55:55:20 - Swigert: "Okay, Houston, we've had a problem here."
55:55:28 - Lousma: "This is Houston. Say again please."
55:55:35 - Lovell: "Houston, we've had a problem. We've had a main B bus undervolt."
55:55:42 - Lousma: "Roger. Main B undervolt."
55:55:49 - Oxygen tank No. 2 temperature begins steady drop lasting 59 seconds indicating a failed sensor.
55:56:10 - Haise: "Okay. Right now, Houston, the voltage is--is looking good. And we had a pretty large bang associated with the caution and warning there. And as I recall, main B was the one that had an amp spike on it once before.
55:56:30 - Lousma: "Roger, Fred."
55:56:38 - Oxygen tank No. 2 quantity becomes erratic for 69 seconds before assuming an off-scale low state, indicating a failed sensor.
55:56:54 - Haise: "In the interim here, we're starting to go ahead and button up the tunnel again."
55:57:04 - Haise: "That jolt must have rocked the sensor on -- see now -- oxygen quantity 2. It was oscillating down around 20 to 60 percent. Now it's full-scale high."
55:57:39 - Master caution and warning triggered by DC main bus B undervoltage. Alarm is turned off in 6 seconds.
55:57:40 - DC main bus B drops below 26.25 volts and continues to fall rapidly.
55:57:44 - Lovell: "Okay. And we're looking at our service module RCS helium 1. We have -- B is barber poled and D is barber poled, helium 2, D is barber pole, and secondary propellants, I have A and C barber pole." AC bus fails within 2 seconds.
55:57:45 - Fuel cell 3 fails.
55:57:59 - Fuel cell current begins to decrease.
55:58:02 - Master caution and warning caused by AC bus 2 being reset.
55:58:06 - Master caution and warning triggered by DC main bus undervoltage.
55:58:07 - DC main bus A drops below 26.25 volts and in the next few seconds levels off at 25.5 volts.
55:58:07 - Haise: "AC 2 is showing zip."
55:58:25 - Haise: "Yes, we got a main bus A undervolt now, too, showing. It's reading about 25 and a half. Main B is reading zip right now."
56:00:06 - Master caution and warning triggered by high hydrogen flow rate to fuel cell 2.
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