Editing Apollo 1 (section)

=== Plugs-out test ===
[[File:Apollo1 Crew im Simulator.jpg|thumb|Chaffee, White, and Grissom training in a simulator of their command module cabin, January 19, 1967]]

The launch simulation on January 27, 1967, on pad 34, was a "plugs-out" test to determine whether the spacecraft would operate nominally on (simulated) internal power while detached from all cables and umbilicals. Passing this test was essential to making the February 21 launch date. The test was considered non-hazardous because neither the launch vehicle nor the spacecraft was loaded with fuel or [[cryogenics]] and all [[pyrotechnic fastener|pyrotechnic]] systems (explosive bolts) were disabled.<ref name="SP4029" />

At 1:00&nbsp;pm [[Eastern Time Zone|EST]] (18:00 [[Greenwich Mean Time|GMT]]) on January 27, first Grissom, then Chaffee, and White entered the command module fully pressure-suited, and were strapped into their seats and hooked up to the spacecraft's oxygen and communication systems. Grissom immediately noticed a strange odor in the air circulating through his suit which he compared to "sour buttermilk", and the simulated countdown was put on hold at 1:20&nbsp;pm, while air samples were taken. No cause of the odor could be found, and the countdown was resumed at 2:42&nbsp;pm. The accident investigation found this odor not to be related to the fire.<ref name="SP4029" />

Three minutes after the count was resumed the hatch installation was started. The hatch consisted of three parts: a removable inner hatch which stayed inside the cabin; a hinged outer hatch which was part of the spacecraft's heat shield; and an outer hatch cover which was part of the boost protective cover enveloping the entire command module to protect it from aerodynamic heating during launch and from launch escape rocket exhaust in the event of a launch abort. The boost hatch cover was partially, but not fully, latched in place because the flexible boost protective cover was slightly distorted by some cabling run under it to provide the simulated internal power (the spacecraft's fuel cell reactants were not loaded for this test). After the hatches were sealed, the air in the cabin was replaced with pure oxygen at {{convert|16.7|psi|kPa|abbr=on|lk=on}}, {{convert|2|psi|kPa|abbr=on}} higher than atmospheric pressure.<ref name="SP4029" /><ref name="aibreport" />{{Reference page|page=181|location=Enclosure V-21}}

Movement by the astronauts was detected by the spacecraft's [[inertial measurement unit]] and the astronauts' biomedical sensors, and also indicated by increases in oxygen spacesuit flow, and sounds from Grissom's stuck-open microphone. The stuck microphone was part of a problem with the communications loop connecting the crew, the [[Operations and Checkout Building]], and the Complex 34 blockhouse control room. The poor communications led Grissom to remark: "How are we going to get to the Moon if we can't talk between two or three buildings?"

The simulated countdown was put on hold again at 5:40&nbsp;pm while attempts were made to troubleshoot the communications problem. All countdown functions up to the simulated internal power transfer had been successfully completed by 6:20&nbsp;pm, and at 6:30 the count remained on hold at T minus 10 minutes.<ref name="SP4029" />