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(WARNING)
RED MESSAGE (CAUTION)
AMBER MESSAGE (ADVISORY)
CYAN MESSAGE (STATUS)
WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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Quick Links

08/11/25

Message Overview:

Message Name:

TRIM DUCT AIR LEAK

Message Code:

B3-007989

Associated CAS:

TRIM AIR LEAK
(Warning)

Reporting LRU: TRIM AIR LEAK
System Description: 36-20-00 - Indicating System
Schematic Diagram: 36-21-00 - Bleed Air Leak Detection System
Wiring Diagram: 36-21-11 - Bleed Air Leak Detection System

Message Description:

A red 'TRIM AIR LEAK' warning CAS message indicates a leak has been detected by the IACS in the Bleed Air Ducting down stream of the #2 Right Flow Control Valve, up to the Pre-Cooler Cross-Over Valve and up to the Trim Air Check Valve.
NOTE: #2 Flow Control Valve is the top valve as installed.

  • Through ARINC bus to the DCU the EICAS has displayed the TRIM AIR LEAK message.

350_trim-air-loop

Possible Causes:

  • Right Flow Control Valve (MPE4)
  • Pre-cooler Cross-over Valve
  • Trim Air Check Valve
  • Trim Loop Sensor 1 (MT61)
  • Trim Loop Sensor 2 (MT36)
  • Trim Loop Sensor 3 (MT69)
  • Trim Loop Sensor 4 (MT124)
  • Loop Routing Interference

Troubleshooting Tips:

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 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.
    • The intermediate pressure system loop element senses a bleed-air leak when the temperature is more than 255°F (123.90°C).

Quick Links:

Removal of the Flow Control Valve AMM 21-51-09-000-801
Installation of the Flow Control Valve AMM 21-51-09-400-801
Removal of the Pre-Cooler Cross-Over Valve AMM 21-61-07-000-801
Installation of the Pre-Cooler Cross-Over Valve AMM 21-61-07-400-801
Operational Test of the Pre-Cooler Cross Over Valve AMM 21-61-07-710-801
Component Location AMM 36-21-00-992-801
Operational Test of the Bleed-Air Leak-Detection and Warning System AMM 36-21-00-710-801
Initiation Test of the Bleed-Air Leak-Detection Loops AMM 36-21-00-740-801
Resistance Check of the Bleed-Air Leak-Detection Loops AMM 36-21-00-760-801
Removal of the Trim-Air-Supply Leak-Detection Element AMM 36-21-09-000-801
Installation of the Trim-Air-Supply Leak-Detection Element AMM 36-21-09-400-801
Removal of the Aft Trim-Air Leak-Detection-Element AMM 36-21-09-000-802
Installation of the Aft Trim-Air Leak-Detection-Element AMM 36-21-09-400-802
Removal of the Forward Trim-Air Leak-Detection-Element AMM 36-21-09-000-803
Installation of the Forward Trim-Air Leak-Detection-Element AMM 36-21-09-400-803
Removal of the Baggage-Compartment Leak-Detection Element AMM 36-21-09-000-804
Installation of the Baggage-Compartment Leak-Detection Element AMM 36-21-09-400-804
Safety Precautions - Maintenance Practices - ALL SPM 20-00-01-02
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02
Electrical Connectors - Maintenance Practice - ALL SPM 20-20-00-02

Troubleshooting Recommendations:

Going into the system diagnostics to the IASC 2 channel B to display the IASC Channel B menu. The IASC LRU test page will provide pages to perform a leak detection system test and check past event locations.

NOTE:

  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 an approximate fuselage/wing station location of the overheat condition.
TRIM AIR LEAK

  • The 0% location starts at the MT124P2 connector under the floor in the baggage bay and the 100% is at the MT61P1 connector mounted to a bracket on the dual heat exchanger.
  • 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.
  • 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 MT124P2 connector under the floor in the baggage bay and the 100% is at the MT61P1 connector mounted to a bracket on the dual heat exchanger.

Leak Detection Test

The test will check all of the loops the IASC is monitoring and pass or fail them. This test is disabled with the wing anti-ice selected on or if aircraft is woffw. Perform the initiation (IBIT) test of the bleed air leak detection loops IAW AMM 36-21-00-740-801.

  • Trim Air loop Information
  • Trim Air Loop schematic
  • The test will identify if the trim loop has a short or open (greater than 62?). MT61, MT36, MT69, MT124 (IASC 2 monitored loop). Check for shorts or open conditions referencing AWM 36-21-11.
    • pre_leak_event_locationpost_leak_event_location

TRIM AIR LOOP Reporting

LRU: IASC 2

Total Loop Length: 358 inches for aircraft

Loop identification in the MDC: MT36

Zero point: Connector number MT124P2 under the baggage bay floor

IASC/Loop Segment ID Location FS/WS Start % MDC Start " Start FS/WS End %MDC End " End °C °F
IASC 2 Trim Air MT124 Under Baggage Bay Duct FS660 0% 0" FS669 12% 41" 124 255
IASC 2 Trim Air MT69 Fwd Trim Air Duct FS669 12% 41" FS756 42% 150" 124 255
IASC 2 Trim Air MT36 Mid/Aft Trim Air Duct FS756 42% 150" FS816 70% 250" 124 255
IASC 2 Trim Air MT61 Trim Supply Duct (FCV to Pre-cooler) FS816 70% 250" FS756 100% 356" 124 255



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