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This case has been updated. Compatible choices are kept; revisit the evidence before drawing your conclusion.
01 / The briefing
Begin with the question.
Apollo 13 launched on April 11, 1970, aiming for a lunar landing. An oxygen-tank failure during the outbound journey forced the crew to abandon that goal and return using the lunar module as a lifeboat. The investigation followed the tank backward through its manufacturing, handling and testing history. Before launch, it had resisted normal draining, so heaters were used to remove the remaining oxygen. That workaround exposed a mismatch between the ground power supply and protective thermostat switches. The tank could finish the procedure while leaving concealed damage behind. Your investigation separates the initiating event in flight from the earlier conditions that made it dangerous, and asks what a successful-looking test actually proves about a component’s health.
The timeline
The heater power specification changes to accommodate 65-volt ground equipment; the thermostat compatibility issue is missed.
Extended heating is used during ground detanking operations.
Apollo 13 launches.
The oxygen-tank accident occurs during the outbound flight.
The crew returns safely to Earth.
The review board presents its findings.
A researched reconstruction for learning. These reasoning steps simplify a complex record; no score can capture the full history.
02 / The evidence
What does the record show?
Read each exhibit before settling on an explanation. The numbered source links below every exhibit lead to the record behind it.
A workaround
The oxygen tank could not be emptied normally, prompting prolonged operation of its heaters to boil off the contents.
Source record [s1]
A protective-device mismatch
The thermostat switches were designed for 28 volts but were exposed to the 65-volt ground supply. Investigators concluded their contacts probably welded closed.
Source record [s1]
Damage outside the instrument range
Excessive heating could damage electrical insulation without the available temperature indication revealing the full temperature excursion.
Source record [s2]
The in-flight trigger
The board connected damaged wiring insulation with a short and combustion inside oxygen tank 2 when its fans were operated.
Source record [s1]
03 / Your reasoning
Follow the strongest explanation.
Choose an interpretation, then compare it with the evidence. You can revise your choice. The goal is understanding, not a perfect score.
04 / The findings
The chain behind the outcome.
The accident’s causal chain crossed organizational and physical boundaries: requirements, ground equipment, switches, test procedures, insulation and in-flight operation. The review board concluded that the high-voltage detanking operation probably disabled the thermostatic protection and allowed damaging heat inside the tank. Later electrical operation provided an ignition opportunity in a highly reactive oxygen environment. Some details were reconstructed from tests and records rather than direct observation inside the failed tank, which is why probability language matters. The crew’s later actions did not create the underlying compatibility problem. The broad lesson is that a workaround can satisfy its immediate objective while invalidating a component’s earlier qualification. A robust review asks not only whether a procedure worked, but whether the hardware remained within its supported conditions, whether protection actually operated and whether instrumentation could reveal a dangerous excursion.
Take the method with you
- Latent damage can begin long before the visible failure.
- Safety devices have operating limits of their own.
- A completed procedure is not automatically a passed health check.
You can read findings at any time. Exploring every reasoning step marks this case as complete in your notebook.
The open record
Sources & further reading
Read the original record and its scope before relying on a conclusion. Source references support the exhibit summaries; Faultory’s reasoning prompts are editorial reconstructions.
- s1NASA — Apollo 13 mission summary and investigation
www.nasa.gov
- s2NASA — Apollo 13 accident
nssdc.gsfc.nasa.gov
- s3NASA — Review Board report retrospective
www.nasa.gov
Written and curated for Faultory by Yunus Emre Vurgun, with AI-assisted research and drafting. Sources and interpretations can need correction. Read our editorial standards or report an issue.