Background
The landing gear door closed proximity sensor failure triggers the warning message: L/G LGCIU 1(2) FAULT, with fault information: L(R) L/G DOOR CLOSED PROX SNSR 26GA(27GA/28GA/29GA).
Recently, the failure of the landing gear door closed proximity sensor on the A32 aircraft led to delays due to MEL release, and this document summarizes the handling procedures.
System Principle
26GA-29GA are the proximity sensors for the main landing gear door closure. Among them, 27GA/29GA are the A/B channels for the left main landing gear door closed proximity sensor, while 26GA/28GA are the A/B channels for the right main landing gear door closed proximity sensor.
The sensor working loop consists of three parts:
—– Sensor: Contains an induction coil.
—– Sensor target: Non-magnetic metal material, stainless steel.
—– Signal processing logic card: Logic control inside LGCIU1&2.
The logic card inside LGCIU sends periodic pulse or sine wave excitation signals to the sensor’s internal induction coil, generating an induced magnetic field. When the target approaches, the induction coefficient (or impedance) of the coil changes, increasing the value of the induction coefficient (or impedance), and the system displays a Target near signal. When the target moves away, the value of the induction coefficient (or impedance) decreases, and the system displays a Target far signal.
Handling Procedures
1. On-Site Handling
(1) For the warning message L/G LGCIU 1 FAULT, fault information L(R) L/G DOOR CLOSED PROX SNSR 26GA(27GA), direct MEL release is not possible, but the faulty proximity sensor can be bypassed with other positions for release. If bypassing the proximity sensor:
1) Prioritize bypassing with the cargo door indication sensors 32WV, 30WV, and release according to MEL52-07-05A for failed cargo door indication (based on frontline feedback experience, 30WV and 32WV are easier to disassemble and take less time).
Note: If releasing according to MEL52-07-05A, ensure that an M item is performed for each flight segment to confirm the cargo door is closed and locked, and notify the MCC to avoid omissions.
2) The proximity sensors 5MJ, 12MJ for the front and rear cargo doors can also be bypassed. 5MJ/12MJ are the proximity sensors controlling the electric operation of the cargo door. If 5MJ/12MJ fail, release can be retained according to MEL52-30-03A for cargo door electric control failure.
(2) For the warning message L/G LGCIU 2 FAULT, fault information L(R) L/G DOOR CLOSED PROX SNSR 28GA(29GA).
1) Direct release can be performed according to MEL32-32-14A/15A, which has fewer restrictions. The M item work mainly involves disconnecting the relevant sensor electrical connectors, and for M items that require sensor gap checks, these can be omitted as described in TR80547229/005. When replacing sensors 26GA/27GA/28GA/29GA, no adjustment is needed because the target is installed inside the upper lock housing, and accessing the target requires opening the upper lock housing, which cannot be done on the wing and must be completed by the component manufacturer in the shop. Additionally, the AMM does not include gap measurement and adjustment for these proximity sensors.
Note: For failures of other landing gear and door proximity sensors, when performing M items, it is not necessary to measure the gaps of all proximity sensors; only the gaps of the currently failed proximity sensors need to be checked.
2) If difficulties arise in releasing according to MEL32-32-14A/15A, such as ground crew at external stations not performing M items, this fault can also be released according to MEL32-32-14B/15B, which requires the failed LGCIU2, has no M item, but the O item is more complex, so it is essential to verify with operations control and the crew in advance whether the release conditions are met.
2. Post-Flight Handling
(1) Refer to the corresponding TSM troubleshooting.
(2) Replacing only the LGCIU or bypassing the LGCIU is not allowed. For fault information L(R) L/G DOOR CLOSED PROX SNSR 26GA(27GA/28GA/29GA), troubleshooting experience indicates that the issues are primarily due to sensor or corresponding connector pin problems, requiring careful measurement of the relevant sensor’s resistance, checking for damage, corrosion, or enlargement of the relevant wiring harness connectors and pins, and isolating the corresponding sensors.
(3) If faults recur after replacing the proximity sensors, according to Airbus TFU32.31.00.039, it may be due to damage, oxidation, corrosion, or wear of the relevant wiring harness connectors or pins, necessitating careful isolation of the wiring harness connectors and pins.
Airbus statistics show that in the A32 fleet, the LGCIU1(2) FAULT and L/G SYS DISAGREE warnings caused by the main landing gear door closed proximity sensors (26GA-29GA) account for 45%. Airbus has initiated an investigation and found that the wiring harness for the main landing gear door closed sensors lacks proper securing, leading to movement of the harness due to vibrations and airflow during aircraft operation, ultimately causing wear and oxidation of the sensor connector pins, increasing contact resistance. The group 320 fleet has also encountered cases of socket pin enlargement during troubleshooting.
3. Special Considerations:
(1) Installing proximity sensors is a mandatory inspection item. During on-site/post-flight handling, if disassembly of proximity sensors is involved, ensure that mandatory inspection personnel are prepared.
(2) For the LGCIU 1 FAULT warning message, bypassing 26GA/27GA and 28GA/29GA is generally not allowed, as this method carries significant risks and may lead to LGCIU1+2 FAULT, resulting in serious situations such as aircraft returning to base.
References
AMM32-31-00-040-003-A
AMM32-31-73-200-001-A
TR80547229
TFU32.31.00.039