IRS Mode Selector Unit & LE Unit Annun.

Question 1

GPS light

Answer 1

• dual channel light
• with a single GPS hardware failure
• GPS, MASTER CAUTION and IRS annunciator illuminate when recall is pressed
• nothing to do with loss of signal
• all lights will extinguish when the MASTER CAUTION system is reset
• with a dual GPS failure
• GPS, MASTER CAUTION and IRS annunciator illuminate immediately
• when you push and release either master caution light, the MASTER CAUTION and IRS annunciator lights go out but the GPS light stays on
• the FMC will then obtain position information using radio (DME) and IRS sensor inputs
• look-ahead terrain alerting and display are unavailable due to position uncertainty

Question 2

ALIGN light (white)

Answer 2

• illuminated (steady) = the respective IRU is operating normally in either the ALIGN mode, the initial ATT mode, or the shutdown cycle
• illuminated (flashing) = alignment cannot be completed, aircraft last position known to IRS is more than 4nm from the position you entered, 3 attempts then you get FAULT light and call mtc
• extinguished = IRS not in the ALIGN mode
• (mode selector in NAV) alignment completed; full IRS data is available
• (mode selector in ATT) attitude information is available; heading information is also available following entry of the initial magnetic heading

Question 3

ON DC light

Answer 3

• illuminated = the respective IRS is operating on DC power from the switched hot bat bus
• AC power is not normal and has been removed
• Battery switch must be on
• 5 sec illumination is normal during alignment (backup DC power self test)
  Note: with loss of normal power, right IRS will only operate for 5 mins on DC power

Question 4

FAULT light

Answer 4

• illuminated = a system fault which affects the respective IRS NAV and/or ATT mode(s) has been detected

Question 5

DC FAIL light

Answer 5

• illuminated when battery power is insufficient to maintain IRU operation (18v)
• CAUTION: if you see both DC FAIL lights illuminated, the switched hot battery bus is not powered or the battery is almost dead! Check bat volts immediately
• loss of battery means loss of alternate DC power to the standby buses

Question 6

LE DEVICES ANNUNCIATOR PANEL

Answer 6

• indicates the position of 2 leading edge (LE) flaps inboard of each engine and 4 LE slats outboard of each engine
• LE flaps have 2 positions, retract and full extend
• LE slats have 3 positions, retract, extend, and full extend
• extinguished = corresponding LE device retracted