Detailed Chronology of Events Surrounding the Apollo 13 accident

Events from 2.5 minutes before the accident to about 5 minutes after

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 - Lousma: ".... 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 
    bus 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.

Apollo 13 Accident Page

Apollo 13 Home Page

NASA Official: Dave Williams, david.r.williams@nasa.gov
Last Updated: 11 December 2003, DRW