Warning Systems - Inhibits

Alert Inhibits

Alerts are inhibited during part of the takeoff in order not to distract the crew. Alerts are also inhibited when they are operationally unnecessary or inappropriate.

Alert messages, except for warnings and messages directly relevant to flight operations, are inhibited during engine start to eliminate nuisance messages.

Alert messages are inhibited individually at other times, such as during the pre-flight and post flight phases or engine shutdown, when they are operationally unnecessary.

EICAS messages are not inhibited during the takeoff.

Some display messages are also inhibited for a brief time period even though system lights are illuminated. This inhibit prevents normal in transit indications from appearing on the display. For example, the GEAR Light illuminates as soon as landing gear retraction begins. However, the associated GEAR DISAGREE display message is inhibited for 25 seconds, allowing sufficient time for normal Landing gear retraction to occur.

Message Consolidation

On the ground with both engines shut down, certain caution and advisory alert messages are inhibited by collecting them into more general alert messages. These include individual fuel, hydraulic, door, and electrical messages. For example, two or more individual entry, cargo, and access door EICAS messages are replaced by the EICAS advisory message DOORS.

Engine Start Message Inhibits

During ground engine start, most new caution and advisory alerts are inhibited from engine start switch engagement until either:

The following messages are not inhibited:

 

Takeoff Inhibits

Warning Inhibits

The Master WARNING lights and fire bell are inhibited for fire during part of the takeoff. The inhibit begins at nose gear extension during rotation and continues until the first to occur:

If a fire occurs during the inhibit, an EICAS warning message appears, but the fire bell and Master WARNING lights do not activate. If the warning condition still exists when the inhibit is removed, the fire bell and Master WARNING lights activate immediately.

Note: Takeoff configuration warnings are terminated at rotation.

Caution Inhibits

The Master CAUTION lights and aural annunciations are inhibited for all cautions during part of the takeoff. The inhibit begins at 80 knots and continues until the first to occur:

If a caution occurs during the inhibit (such as rejected takeoff is initiated above 80 knots) and exists on the ground when the airspeed decreases below 75 knots, both Master CAUTION lights and aural activate.

Note: EICAS caution messages are not inhibited during takeoff.

If the master CAUTION lights and the aural alerts are activated prior to the inhibit, they continue to illuminate and sound. The inhibit cannot reset the lights or aural alert.

Advisory Inhibits

The following EICAS advisory messages are inhibited on takeoff:

  • DATA LINK LOST to indicate data link is temporarily unavailable.
  • WINDSHEAR SYS to indicate windshear alerting functions are inoperative.

The inhibit begins from the time either engine is advanced to takeoff thrust and continues until the first to occur:

  • 400 feet AGL, or
  • 20 seconds after rotation

All other EICAS advisory messages are not inhibited on takeoff.

Communication Inhibits

The following are inhibited during takeoff:

  • EICAS communication alert messages such as SELCAL, ACARS, ATC or PRINTER and associated aural chimes. The •CABIN ALERT message and its chime are not inhibited.

The inhibit begins from the time either engine is advanced to takeoff thrust until the first to occur:

Inhibits are cleared on the ground with both engines below takeoff thrust. If a communication alert message occurs during the inhibit and exists when the inhibit ends, the EICAS alert message and aural chime activate.

Landing Inhibits

Communication Inhibits

The following are inhibited during landing:

  • EICAS communication alert messages such as SELCAL, ACARS, ATC or PRINTER and associated aural chimes. The •CABIN ALERT message and its chime are not inhibited.

The inhibit begins on descent at 800 feet AGL (Radio Altitude) and terminates at:

  • less than 75 knots groundspeed
  • 900 feet AGL (Radio Altitude) on missed approach

If a communication alert message occurs during the inhibit and exists when inhibit ends, the EICAS alert message and aural chime activate.

Engine Shutdown Inhibits

Engine-driven pumps, generators, and other components whose alert messages would result from an engine shutdown are inhibited by the ENG SHUTDOWN message. When an engine is shutdown (FUEL CONTROL switch in CUT OFF or fire handle pulled), the EICAS alert message L ENG SHUTDOWN or R ENG SHUTDOWN is displayed and the following L or R alerts are inhibited:

 

When the airplane is on the ground and both FUEL CONTROL switches are in the CUT OFF position, the master CAUTION lights and the caution alert beeper are inhibited. This prevents alerts associated with routine gate operations from triggering nuisance lights and aural alerts.

When the shutdown inhibit is removed, the master CAUTION lights and alert beeper do not activate for alerts that existed prior to its removal. For example, if the right hydraulic system is depressurized with both engines shutdown, and the left engine is then started, the master CAUTION lights and beeper do not activate. The master CAUTION lights and beeper activate only when the alert first occurs, provided no other inhibit is in effect.

Alert Message Inhibits

Alert message inhibits are those inhibits where one message is inhibited by the presence of another alert message. For example, individual fuel or hydraulic pump pressure messages are inhibited by higher priority system pressure messages.

Certain alert messages are time delayed, even though discrete system lights may illuminate. Time delay inhibits prevent normal in-transit indications from appearing as EICAS system alert messages. For example, valves are generally only sensed open and/or closed, not in-transit. When a valve is in-transit, the alert message indicating the valve has failed to open or close is inhibited to allow the valve time to move to the commanded position. If the valve is not in the commanded position at the end of the inhibit period, an EICAS system alert message is displayed.

Altitude Alerting Inhibit

Altitude alerting is inhibited in flight with all landing gear down and locked.

Master Caution Lights and Beeper Inhibit

The master CAUTION lights and the associated alert beeper are inhibited for the L/R ENG SHUTDOWN caution level message.

Warning System