L BLEED LEAK
(Warning)

A red 'L BLEED LEAK' (Warning) Crew Alerting System (CAS) message indicates a leak has been detected by MT67 LH bleed air loop in the air conditioning pack ducting.

• The Integrated Air System Controller has detected a bleed air leak between the ducts for Left Intermediate Pressure Valve (LH IPV) the Left Air Turbine Starter (LH ATS) interface the Cross-Bleed Valve (CBV) and the Left Flow Control Valve (LH FCV). Through ARINC bus from the Integrated Air System Controller (IASC) to the Data Concentrator Unit (DCU) the Engine Indication and Crew Alerting System (EICAS) displays the red 'L BLEED LEAK' warning CAS message.
• L BLEED LEAK is detected with a Single Loop System.

• Intermediate Pressure Valve (IPV) (V3)
• Plumbing Leak
• Bleed Loop Routing
• Left Bleed Loop Sensor 1 (MT67)

Advisory Wire/Service Bulletin:

• AW300-30-0354 - Potential Piccolo Tube Damage When Replacing a Bleed Loop Element

Full Throttle Blog/Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

• Troubleshooting Guide for Bleed Loops
• Bleed air loops are the detection element used to indicate that a leak has occurred in the bleed air system.

  • The ducting has a insulation cover that will contain the air leaking from the ducting routing it to a insulation vent hole.
  • 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 IASC controller senses that the outer conductor is grounded and supplies the inner conductor with alternating current for its resistance measurement. The IASC controller measures this resistance and shows the correct message on the EICAS.
  • The intermediate pressure system loop element senses a bleed-air leak when the temperature is more than 255°F (123.90°C).

Going into the system diagnostics to the IASC 1 channel B (left system fault) Channel B menu. 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.

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 approximate fuselage/wing station and percentage 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.
L BLEED LEAK

• 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

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. Perform the initiation (IBIT) test of the bleed air leak detection loops IAW AMM 36-21-00-740-801.
NOTE: If the LH Bleed Loop is shorted the IASC will post a 'L BLEED LOOP FAIL' (Caution) CAS, along with one MDC fault message.

• LH Bleed loop schematic and information (MT67).
• The test will identify if the respective LH loop has a short or open (greater than 75Ω). MT67 (LH system loop). Perform resistance checks on the applicable loop per AMM 36-21-00-760-801.

Select an MDC Fault Code/Message:B3-007016 - L BLEED DUCT AIR LEAK [L BLEED AIR LEAK]