Chronology of Events Surrounding the Apollo 13 Accident

The following includes 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.

Return to Apollo 13 Description Page

Updated January 24, 2006
Charles Redmond, Author
Steven J. Dick, NASA Chief Historian
Steve Garber, NASA History Web Curator
For further information E-mail histinfo@hq.nasa.gov