L PYLON BLEED LEAK
(Warning)

A red 'L PYLON BLEED LEAK' (Warning) CAS message indicates a bleed air leak in duct work between the power plant interface and the left Intermediate Pressure Valve (IPV) and the left High Pressure Valve (HPV), or short circuit in the Left Hand Pylon loop.

NOTE: The pylon bleed loop is a dual loop system.

• Left Bleed Loop Sensor 1 (MT67)
• Left Pylon Loop 1 Channel A (MT63)
• Right Pylon Loop 2 Channel B (MT44)
• Associated Wiring

Advisory Wire/Service Bulletin:

• AW300-30-0354 - Potential Piccolo Tube Damage When Replacing a Bleed Loop Element
• AW300-36-0387 - Bleed Air Leak Detection Loop Elements

Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

Troubleshooting Guide for Bleed Loops

• Leak detection sensors monitor the bleed air lines from the pylon and along the leading edge piccolo tubes for unacceptable leaks in the system
• There are two loops along each line, IASC 1 channel B monitors loops RH Pylon/Wing Loop and LH Fuselage/Wing Loop. IASC 2 channel B monitors RH Fuselage/Wing Loop and LH Pylon/Wing Loop
• Each loop element has a concentric outer conductor, a layer of eutectic salt compound and an inner conductor. The loop elements are connected to the IAS controllers through the routing of the usual aircraft harnesses
• The loop elements are electrically connected in series and the concentric outer conductor is connected to the aircraft ground. The layer of eutectic salt compound insulates the outer conductor from the inner conductor. When hot bleed-air gets on the loop element, the eutectic salt compound becomes conductive and lets the outer conductor make contact with the inner conductor. The IAS controller senses that the outer conductor is grounded and supplies the inner conductor with alternating current for its resistance measurement
• The IAS controller measures this resistance and shows the correct message on the EICAS
• If the temperature in the area of the wing anti-ice ducts is more than 460°F (237.80°C), the loop element in that area senses a bleed-air leak

Go into the system diagnostics to the IASC 1 channel B (L Pylon Loop). The IASC LRU test page will provide pages to perform a leak detection system test and check past event locations.

1. Locate the short circuit or leak using the Leak Event location function.
2. Check for short circuit at the corresponding connector.
3. Check the loop routing for a fouling condition on a hot surface (loop touching duct).
   NOTE: Before replacing a loop always look at the loop for routing, ensure loop is not too close to the plumbing or the bleed hole on a valve. Review AMM 36-21-00-992-801 for component location. See individual loops for specific routing information.
4. Use a Tegam meter to check capacitance and inductance between the inner and outer conductor of the corresponding loop. Perform the impedance check per the Leak detection how to.
5. Do the close out.

Leak Event Location History

The Leak Event Location History will identify when the system posted a fault, what loop failed and a general location based on the approximate fuselage/wing station location of the overheat condition.

The CH350 reports the name of the bleed loop and fuselage station or wing station and general location of the leak in percentage. A 0% location starts at the beginning of the loop and the end of the loop is 100% so a 5% indication will be 5% of the total loop length.

• When a location is identified in the leak event location history, Inspect the plumbing for possible leaks
• If the leak can not be identified, perform the system functional check IAW AMM 36-21-00-710-801

Leak Detection Test

1. The test will check all of the loops the IASC is monitoring and pass or fail them. This test may fail if there is a lot of action going on in the IASC, retesting may pass the failed loops. This test is disabled with the wing heat system on.
   NOTE: If the LH Pylon Bleed Loop is SHORTED/OPEN the IASC will post a L PYLON LOOP FAIL (Cyan) CAS, along with two MDC fault messages.

   • L Pylon Bleed Loop schematic and information
   • L Pylon and Wing loop information
   • L Pylon and Wing loop schematic

   1. The test will identify if the LH Pylon/Wing bleed loops have a short or open (> 136 Ω). Perform resistance checks on the applicable loop per AMM 36-21-00-760-801.

   LOOP	VALUE (OHMS)
   LH and RH Pylon	14 Ω

2. Select the associated MDC Fault message:
   Select the MDC MessageB3-007118 - L PYLON DUCT AIR LEAK [L PYLON AIR LEAK]
3. Do the close out.