Auto Mode Operation (Contd.)

An amber AUTO FAIL light illuminates if any of the following conditions occurs:

  • Loss of DC power
  • Controller fault
  • Outflow valve control fault
  • Excessive differential pressure (> 8.75 psi)*
  • Excessive rate of cabin pressure change (±2000 sea level feet/minute)*
  • High cabin altitude (above 15,800 feet).*

*If controller is not responding properly.


With illumination of the AUTO FAIL light, the pressure control automatically transfers to the
other auto controller (ALTN mode). Moving the pressurization mode selector to the ALTN
position extinguishes the AUTO FAIL light, however the ALTN light remains illuminated to
indicate single channel operation.