Some of the most important doors around the aircraft have sensors to give the flight crew an indication of an incorrect door position. The engine indicating and crew alerting system (EICAS) shows a message on the primary flight display and causes an alarm to operate if a door is not closed correctly. The master caution and warning light system also operates. During takeoff and landing, some messages from proximity sensors may not be shown on the EICAS. This is to prevent an overload on the flight crew at these important times.

The type of sensor used on the applicable doors is a proximity sensor. With electrical power energized, unless each sensor output condition is satisfactory for the applicable phase of flight or ground maneuver, the warning system operates.

These proximity sensors supply the proximity-sensor electronic unit (PSEU) with door status data. The PSEU uses this data to supply the necessary signals to the data concentrator unit (DCU) of the EICAS. The EICAS shows the applicable door caution/status messages on the crew alerting system (CAS) messages area of the multi-function display (MFD).

The function of the door warning system is to give the flight crew visual and sound indications if there is an incorrect door position.

The door warning system uses three types (type 1, type 2, and type 3) of proximity sensors. The proximity sensors sense the proximity (near or far status) of targets on the aircraft. The proximity-sensors are electromagnetic coils that give an electronic signal when near the targets. The proximity sensors and the targets do not touch each other.

There are three proximity sensors which give an indication in the flight compartment for the passenger door condition. One sensor (type 2) is installed in the door adjacent to the locking hook, and it senses that the door is locked. A second sensor (type 2) is installed adjacent to the pivot shaft of the external door handle. It senses that the external door handle is in a closed position.

The remaining sensor (type 3) is found on the fuselage door frame adjacent to one of the door stop fittings. This sensor is spring-loaded to prevent unwanted indications on the engine indication and crew alerting system (EICAS) because of small movements of the door in flight. It senses that the door is in its opening. A cover is installed on this sensor to prevent damage.

The flight compartment indication of a baggage door closed condition is given by a proximity sensor (type 1) installed adjacent to the forward shoot pin. It senses that the door is latched. This sensor is spring-loaded to prevent unwanted indications on the EICAS because of small movements of the door in flight. The other sensor (type 2) is near the handle. It senses that the door is locked because the handle is in the closed position.

This door has one proximity sensor (type 2) installed on the door frame structure adjacent to the roller arm of the latch.

The over-wing emergency exit has a proximity sensor (type 1) installed on the fuselage frame adjacent to one of the shoot pins. The flight compartment indications operate if the shoot pin is not fully engaged. This sensor is spring-loaded to prevent unwanted indications on the EICAS because of small movements of the door in flight.

The battery access door has one proximity sensor (type 2) installed adjacent to the stop fitting of the latch.

The EICAS through the data concentrator unit (DCU) and the master caution and warning system control and supply the visual and sound indications in the flight compartment.

The DCU receives inputs from the proximity-sensor electronic unit (PSEU). The PSEU monitors the condition of the doors through signals from the proximity sensors. The PSEU receives inputs from other systems and uses control logic to calculate the output to the EICAS.

The door warning system uses proximity sensors to sense the proximity of magnetic targets installed on the aircraft. The proximity sensors have electro-magnetic coils that give an electronic signal when near the magnetic targets. This lets the proximity sensors function with no contact with the targets.

The PSEU constantly monitors the door proximity-sensor signals. When a sensor moves away from a target, a signal is sent to the PSEU to show that a door is not correctly closed. When this occurs in flight or on the ground with power to the left engine, the primary EICAS shows an amber caution message. On the ground with no engines powered, the primary EICAS shows a white status message for the PASSENGER DOOR and the CARGO DOOR when either of those doors are not correctly closed. Also, there will be one chime as an aural warning.

The following EICAS messages are related to the door warning system: 

To decrease pilot work load in critical phases of flight, the EICAS messages that follow are not shown during landing and takeoff:

The PSEU does a continuous built-in test (BIT) of all signals and sensors in the door warning system. If the BIT finds a system, sensor or signal which is defective, the PROX SYS FAULT advisory message (cyan) shows on the EICAS.