Panels 3 and 16 had been merged with Panel 18 on February 23. In its final report to the Review Board, Panel 18 listed:
Several arcing indications were observed in the CM left front sector and a voltage transient was noted in all three phases of AC Bus 2. This transient was most closely simulated by a power interruption or short circuit on DC Bus B. Physical evidence and witness statements indicated the progress of the fire to be from the left side of the spacecraft. Simulations and tests indicated that combustion initiation by electrostatic discharge or chemical action was not probable. No physical evidence of prefire overheating of mechanical components or heating devices was found.
No single ignition source could be conclusively identified. The most probable initiator was considered to be the electrical arcing or shorting in the left front sector of the spacecraft. The location best fitting the total available information was that where environmental control system instrumentation power wiring ran into the area between the environmental control unit and the oxygen panel.
All spacecraft records were reviewed by the various panels and the results were screened by Panel 18.
No evidence was found to correlate previously known discrepancies, malfunctions, qualification failures or open work items with the source of ignition.
At the time of the observed fire, data including telemetry and voice communications indicated no malfunctioning spacecraft systems (other than the live microphone).
Existing spacecraft instrumentation was insufficient by itself to provide data to identify the source of ignition.