The function of the position indication system is to give the flight crew visual indications of the state and position of the landing gears, ground spoilers, and some important doors on the aircraft. The position indication system also sends the same data to other aircraft systems for their usual operation.

In its usual operation, the position indication system interfaces with other aircraft systems to receive different sensor data.

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Each MLG (left and right) has five non-contact induction-based proximity sensors to determine the near/far status of the magnetic proximity targets.

There are two weight-on-wheels (WOW) proximity sensors, two downlock proximity sensors, and an uplock proximity sensor in each MLG.

These sensors send electrical signals to the PSEU to indicate the state and position of the MLG.

MLG Gear Down & Locked Sensors

Each MLG (left and right) has five non-contact induction-based proximity sensors to determine the near/far status of the magnetic proximity targets.

There are two weight-on-wheels (WOW) proximity sensors, two downlock proximity sensors, and an uplock proximity sensor in each MLG.

These sensors send electrical signals to the PSEU to indicate the state and position of the MLG.

MLG Gear Down & Locked Sensors

Landing Gear Down and Locked are monitored via dual redundant sensors. Gear Down and Locked Indication #2 are independent of Down and Locked Indication #1 and the Extend Control function.

RGDLK1 (PX08), RGDLK2 (PX38), LGDLK1 (PX09), LGDLK2 (PX39) are the sensors used to determine the main landing gear is down and locked. Independence is achieved by monitoring each down lock sensor on a separate PSC channel.

The targets are within the MLG extend cylinder and are the most sensitive to adjust. These proximity sensors are bottomed out, then turned out a fraction of a turn for proper orientation.

MLG Up and Locked Indication

Landing Gear Up and Locked is monitored via individual sensors on each gear.

RGUPLK (PX04), LGUPLK (PX05) are the sensors used to monitor the main landing gear up lock indication.

The sensor is on the up lock actuator, as the gear closes into the fully retracted position, the inductance of the prox sensor should change indicating the target is near and the gear is secure.

Up lock indication is used to indicate to the display the green cross hatched box showing the gear is up and locked.

MLG WOW Indication

The main gear have a dual proximity sensor on each gear set up for redundancy in determining that the aircraft has weight on wheel indication.

RGWOW1 (PX01), RGWOW2 (PX31), LGWOW1 (PX02), LGWOW2 (PX32) make up the main landing gear targets.

The picture shows the aircraft on jacks and weight off the wheels. In this position steel targets are needed to simulate Weight on Wheels. While on the ground to simulate air mode, non ferrous oxygen free copper (non) targets need to be used to make the system ignore the metal targets, this location is much harder to get to when the trailing link is collapsed with aircraft weight.

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The NLG has seven non-contact induction-based proximity sensors to determine the near/far status of the magnetic proximity targets.

In the NLG there are two weight-off-wheels (WOFW) proximity sensors, two downlock proximity sensors, two door proximity sensors, and an unlock proximity sensor. There is also a centered limit switch in the NLG.

These sensors send electrical signals to the PSEU to indicate the state and position of the NLG.

Nose Wheel Centered and Weight On Wheels

Nose Wheel centered and weight on wheels (WOW) is monitored on the Nose Gear. Centering and WOW indication is accomplished using the same target and sensor (a redundant pair).

NGWOW1 (PX03), and NGWOW2 (PX33) make up the sensors for the nose wheel centered, and weight on wheels.

The two functions share common software trip points. The near/far trip point for both applications is 7.8. Using this trip point, a nose wheel centered indication will occur at target rotation angles no greater than 2.78 degrees (7.8 mH @ 0.048 Gap). Earliest indication is at 2.63 degrees (7.9 mH @ .053 Gap). These figures apply at full strut extension with the centering cam engaged, as the strut is compressed, indication will occur at progressively smaller angles as the WOW function is lowering the sensor inductance even through the nose wheel is still centered.

Nominally WOFFW indication will occur between the strut compression distances of 1.117 and 1.446 inches. Earliest indication is at 8.84 degrees of target rotation (7.7 mH @ 0.043 Gap). These figures apply only when the nose wheel is centered, WOW indications may occur at smaller angles as the nose wheel moves from center.

The picture shows the aircraft is on jacks and the targets are in close proximity to the sensors indicating weight off wheels and nose gear centered. To simulate ground and off center inputs, non ferrous oxygen free copper (non) targets need to be used to make the system ignore the metal targets.

With weight on wheels, steel targets are required to simulate Weight Off Wheels.

NLG Down and Locked Indication

The nose gear has a dual proximity sensor set up for redundancy in determining that the aircraft nose gear system is down and locked.

NGDLK1 (PX10), and NGDLK2 (PX40) are the sensors that indicate the nose gear is down and locked.

Nose Gear Door Closed

Nose Gear door is monitored via individual sensors, LNGDRCL (PX34) and RNGDRCL (PX35).

The dual sensors are on the forward side of the aircraft nose wheel bay left and right hand sides.

As the gear closes into the fully retracted position, the inductance of the prox sensor should change indicating the target is near and the gear is secure.

The sensors will illuminate the NOSE GEAR DOOR CAS message when the nose gear up lock (NGUPLK PX06) target is near and both gear door sensors indicate far.

MDC errors will be reported when the individual sensors post "far" indications.

The door is mechanically linked to the nose gear, they close with a 300 lbs pre load to prevent inadvertent opening during flight.

Nose Gear Up & Locked

Nose Gear Up and Locked is monitored via individual sensor.

The NGUPLK (PX06) sensor is on the up lock actuator, as the gear closes into the fully retracted position, the inductance of the proximity sensor should change indicating the target is near and the gear is secure.

Nose Gear Up & Locked

Nose Gear Up and Locked is monitored via individual sensor.

The NGUPLK (PX06) sensor is on the up lock actuator, as the gear closes into the fully retracted position, the inductance of the proximity sensor should change indicating the target is near and the gear is secure.

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The Proximity Sensor Electronic Unit (PSEU) is in the right equipment rack. It gets 28 VDC power from the L MAIN BUS, R MAIN BUS, L ESS BUS, and R ESS BUS.

The PSEU has a two-channel configuration which processes the input signals from the proximity sensors and other aircraft sensors. Some sensors give the same signals to each channel (A and B) for safer operation.

The PSEU calculates the input data and sends the results to the data concentrator unit (DCU) for display on the EICAS. The PSEU also sends the same data to other aircraft systems for their usual operation.

The PSEU communicates with the maintenance diagnostic computer (MDC) through the ARINC 429 bus.

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The proximity sensors sense the near/far status of the magnetic proximity targets. The status is transmitted to the PSEU which processes the signals. The PSEU calculates the logical equations for:

• Weight-on-wheels (WOW)
• Weight-off-wheels (WOFW)
• The nose gear door position
• The aircraft doors position
• The spoilers position
• The MLG and NLG position.

The results of these equations are sent as discrete outputs and ARINC signals to other aircraft systems.

The EICAS through the DCU receive inputs from the PSEU and control the visual indications given in the flight compartment.

The PSEU constantly monitors the landing-gear proximity-sensor signals. When a sensor moves away from a target, a signal is sent to the PSEU to show that a landing gear is not correctly set. If the aircraft is in a possible landing configuration and the gear is not down and locked, warning indications will be given. When this occurs the EICAS shows a GEAR warning message and an aural warning output is supplied.

The GEAR DISAGREE caution message will show when one of the following conditions occur:

• Landing gear does not reach the position that agrees with the landing-gear control handle within the maximum gear swing timeout
• Landing gear fails to move when commanded
• Uncommanded movement of the landing gear

The GEAR SYS FAIL caution message will show when one of the following conditions occur:

• The loss of the gear indication
• The loss of the ARNIC output from the PSEU

The NOSE GEAR DOOR caution message will show when either the left or right nose gear door is open and the gear is up and locked.

The WOW FAIL caution will show when one of the following conditions occur:

• Two of the WOW sensor inputs have malfunctioned
• Two of the WOW sensor inputs are unreasonable
• The WOFW override mode is enabled
• Malfunction of the critical WOW individual discrete output (DOT19A, NGDNLK, SCU, A073)
• Malfunction of the critical WOW discrete output pairs (DOT02A/DOT02B, DOT04A/DOT04B, DOT12A/DOT12B)
• Malfunction of the PSEU channel A
• One of the two NGWOFW sensors is unreasonable near
• One of the two NGDLK sensors is unreasonable far

The PROX SYS FAULT advisory message will show when one of the following conditions occur:

• A malfunction in the proximity sensor system that does not require flight crew action
• The loss of the ARINC 429 output from a single channel

The EICAS messages that follow are related to the position indication system:

EICAS MESSAGE(S)	LEVEL (COLOR)
GEAR	WARNING (red)
GEAR DISAGREE	CAUTION (amber)
GEAR SYS FAIL	CAUTION (amber)
NOSE GEAR DOOR	CAUTION (amber)
WOW FAIL	CAUTION (amber)
PROX SYS FAULT	ADVISORY (cyan)

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The position indication system has interfaces with the systems/components that follow:

The MDC questions the PSEU for rigging/status of the inputs/outputs. The PSEU responds to the MDC question, and finds the correct display screen to show. The data on the screen includes instructions, warnings and test condition pre-requisites. The rigging display menu is to help the maintenance crew to accurately adjust the proximity sensors in their near state. The rigging display is interactive, in that the page display will change based on the sensor position in proximity to the target.

The NLG is monitored for center position and door positions. The MLGs and the NLG are monitored for the gear in movement and if there is a gear disagree. They are also monitored for the down and locked position, and the up and locked position. These signals are supplied to the EICAS through two independently isolated ARINC 429 busses for the display of the position of each gear.

The landing-gear position display is shown on the primary EICAS page with color.

The landing gear downlocked and safe condition is shown with a DN legend in black inside a solid green circle. To get this display one of the two downlock sensors senses that the landing gear is down and locked.

When the landing gear is up, the indication can be shown in three different color legends as follows:

• An UP legend in white inside a white outline box. This indicates that the landing gear is up with no gear warning and either there is no gear disagree or a gear disagree with the landing-gear control handle set UP.
  
  
• An UP legend in black inside a solid amber box. This indicates that the landing gear is up with no gear warning, no gear disagree and the landing-gear control handle is not set to UP.
  
  
• An UP legend in black inside a solid red box. This indicates that the landing gear is up with a gear warning.

Note:
For the up condition the uplock sensor senses that the gear is up and the two downlock sensors sense that the gear is not downlocked.

When the landing gear is in movement, the indication can be shown in three different color legends as follows:

• A white filled box with a white outline and black hatch lines. This indicates that the landing gear is in transit with no gear disagree, and no gear warning.
  
  
• An amber filled box with an amber outline and black hatch lines. This indicates that the landing gear is in transit with a gear disagree, and no gear warning.
  
  
• A red filled box with a red outline and black hatch lines. This indicates that the landing gear is in transit with a gear disagree, and no gear warning.

Note:
For the movement condition the uplock and downlock sensors sense that the gear is not locked.

When the data from the PSEU is not available or incorrect on both of the ARINC 429 busses, two magenta dashes are shown inside a black filled box with a magenta outline.

PSEU System Rigging / Status Menu

Entering the MDC maintenance screen for the PSEU allows access to several sub screens to do the following tasks:

• Proximity sensor status, sensor ID information, health, status, near far, inductance in millihenry is available for setting the sensor. There are three pages for the three different types of sensors, gear, doors, and spoilers.
  
  
• PSEU discrete input status menu, three pages of the input, ID, name, health, and status are available.
• PSEU discrete output status menu, eight pages of the output, ID, name, health, and status are available.
• PSEU power bus status menu, displays the status of the left and right bus information.

For rigging, setting up the proximity sensors using feeler gages and proximity sensor rotation after bottoming out are the primary ways to set the correct gap and verifying the status with the MDC.

PSEU Rigging and Status Options

After selecting the PSEU system rigging page, options of four different sensor and discrete information is available from this page.

• Proximity Sensor Status Menu, selecting this page will ask to select the Gear, Door, and Spoiler subsystems. This is where individual sensor information is displayed.
  
  
• PSEU Discrete Input Status Menu, selecting this page will display three pages of individual input discrete information.
• PSEU Discrete Output Status Menu, selecting this page will display 8 pages of individual output discrete information.
• PSEU Input Power Bus Status Menu, selecting this page will display the power the PSEU is operating on.

Proximity Sensor Status

The proximity sensor page displays the list of sensors by sensor number and general description.

When a selected sensor is high-lighted, detailed information is displayed below the page brake.

Note:
This page is displaying the sensor as failed, the sensor is too far from the target looking at the Near+ Near- indication in the middle of the lower right page. When the sensor is on target, an X is displayed on the indicator with the correct inductance for that position.

Options for the sensor health are, OK, SHORT, OPEN, H/W FAILURE, RIGGING ERROR.

Options for the sensor status are, NEAR, FAR.

PSEU Discrete Input and Output Status

There are three pages of discrete inputs and eight pages of discrete outputs that can be selected to view detailed information from the discrete input / output status menu page.

When a selected output is high-lighted, detailed information is displayed below the page break.

Options for the discrete input health are OK, SHORT, OPEN, FAIL.

Options for the sensor status are ACTIVE, INACTIVE.

PSEU Input Power Bus Status

The 28 VDC bus health status shows the voltage applied to the PSEU from the Left & Right Main Bus, Left & Right Essential bus.

The bus status is also shown as ACTIVE, or INACTIVE.

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The PSEU includes an override test mode. This provides an option to the crew to override the PSEU into the ALL GEAR WEIGHT OFF WHEELS (WOFW) MODE, without reference to the current mode of the aircraft. This mode prevents the use of the sensor anti-targets and has the aircraft WOFW mode controlled by the PSEU through the MDC.

The selection of the override mode through the MDC interface is possible only when the aircraft is in ground mode. The override mode lets specified PSEU discrete outputs and ARINC signals be sent to the interface line replaceable units (LRUs) to show the in air mode without reference to the WOW sensors. When the mode is set, through the MDC, a WOW FAIL amber message shows that the override mode is active.

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
PX09	MAIN LANDING-GEAR DOWNLOCK 1  PROXIMITY-SENSOR (LH)	ZONE(S) 730	32-61-01
PX39	MAIN LANDING-GEAR DOWNLOCK 2  PROXIMITY-SENSOR (LH)	ZONE(S) 730	32-61-01
PX08	MAIN LANDING-GEAR DOWNLOCK 1  PROXIMITY-SENSOR (RH)	ZONE(S) 740	32-61-01
PX38	MAIN LANDING-GEAR DOWNLOCK 2  PROXIMITY-SENSOR (RH)	ZONE(S) 740	32-61-01
PX05	MAIN LANDING-GEAR UPLOCK  PROXIMITY-SENSOR (LH)	ZONE(S) 730	32-61-01
PX04	MAIN LANDING-GEAR UPLOCK  PROXIMITY-SENSOR (RH)	ZONE(S) 740	32-61-01
PX02	MAIN LANDING-GEAR WEIGHT-ON-WHEELS  1 PROXIMITY-SENSOR (LH)	ZONE(S) 730	32-61-01
PX32	MAIN LANDING-GEAR WEIGHT-ON-WHEELS  2 PROXIMITY-SENSOR (LH)	ZONE(S) 730	32-61-01
PX01	MAIN LANDING-GEAR WEIGHT-ON-WHEELS  1 PROXIMITY-SENSOR (RH)	ZONE(S) 740	32-61-01
PX31	MAIN LANDING-GEAR WEIGHT-ON-WHEELS  2 PROXIMITY-SENSOR (RH)	ZONE(S) 740	32-61-01
PX34	LEFT NOSE LANDING-GEAR DOOR CLOSED  PROXIMITY SENSOR	ZONE(S) 711	32-61-05
PX10	NOSE LANDING-GEAR DOWNLOCK 1  PROXIMITY-SENSOR	ZONE(S) 710	32-61-05
PX40	NOSE LANDING-GEAR DOWNLOCK 2  PROXIMITY-SENSOR	ZONE(S) 710	32-61-05
PX06	NOSE LANDING-GEAR UPLOCK  PROXIMITY-SENSOR	ZONE(S) 710	32-61-05
PX03	NOSE LANDING-GEAR WEIGHT-OFF-WHEELS 1 PROXIMITY-SENSOR	ZONE(S) 710	32-61-05
PX33	NOPROXIMITY-SENSORSE LANDING-GEAR WEIGHT-OFF-WHEELS 2	ZONE(S) 710	32-61-05
PX35	RIGHT NOSE LANDING-GEAR DOOR  CLOSED PROXIMITY SENSOR	ZONE(S) 712	32-61-05
A9	PROXIMITY-SENSOR ELECTRONIC UNIT (PSEU)	ZONE(S) 222DZ	32-61-09

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