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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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09/04/19

Bleed Leak Detection System Troubleshooting Guide

Introduction

Terminology

Acronym Definition Acronym Definition
ACS Air Conditioning System AIPS Airframe Ice Protection System
APU Auxiliary Power Unit ATS Air Turbine Starter
CBIT Continuous Build In Test CBW Wing Cross Bleed Valve
CH Channel Element Hot Air Leak Detection sensor with a connector on each ends
F.S. Fuselage Station FCV Flow Control Valve
HARSOV Hot Air Regulating and Shut-Off Valve HPGC High Pressure Ground Connection
HPV High Pressure Valve IASC Integrated Air System Controller
IBIT Initiated Built In Test IPV Intermediate Pressure Valve
Loop Assembly of several Elements connected together in series to detect Hot Air Leaks in a given system.
(e.g. L Bleed Loop A, R Fuse Loop B.		 MDC Maintenance Diagnostic Computer
PBIT Power Up Build In Test PCV Pre-cooler Crossover Valve
TCV Temperature Control Valve WAIV Wing Anti-Ice Valve
W.S. Wing Station    

System Description

The ACS bleed leak detection system ducting is divided into 6 distinctive zones and the AIPS bleed leak detection system is divided in 3 distinctive zones. It shall be noted that 2 zones (the LH and RH pylon) are common to the ACS and AIPS bleed leak detection system.

Bleed leak detection loop for the ACS:

  • The left bleed leak detection loop: covers the ducts between the LH IPV the LH ATS interface, the CBV and the LH FCV.
  • The right bleed leak detection loop: covers the ducts between the RH IPV the RH ATS interface, the CBV, the RH FCV, the HPGC interface and the APU interface.
  • The trim air bleed leak detection loop: covers the trim air ducts located between the pre-cooler in the AFT equipment bay and the mix manifold under the baggage compartment floor.
  • The pack bleed leak detection dual loops: covers the remaining ducts between the 2 FCV and the pack.

Bleed leak detection loop common to the ACS and AIPS:

  • The right pylon dual loops: covers the duct between the power plant interface and the right IPV (part of ACS system) and right HPV (part of AIPS)
  • The left pylon dual loops: covers the duct between the power plant interface and the left IPV (part of ACS system) and left HPV (part of AIPS)

Bleed leak detection loop for the AIPS:

  • The anti-ice ducting dual loops: covers all the ducting downstream of both HPV down to the end of the piccolo ducts (including CBW)

The pylon, the anti-ice and the pack bleed leak detection system is composed of two loops. Each loop is composed of several elements connected in series. One loop is connected to the Channel B of the IASC1 and the other set is connected to the Channel B of the IASC2.

Figure 1: Dual Loop Architecture

Based on the line resistance and insulation values of each loop, the IASC will then display the appropriate EICAS and MDC messages

Loops Arrangement for the AIPS and Pylon

Loop Name Connected to IASC # Zone
1 Pylon Associated Pylon
2 Fuse Wing Associated Anti-Ice
3 Pylon Wing Opposite Anti-Ice

  • 2 zones per side
  • 3 loops per side
  • both sides are symmetrical

The alarm temperatures are as follow:

  • 237.8°C (460°F) in the wings
  • 123.9°C (255°F) elsewhere

NOTE: To have a leak message on EICAS, both sensing elements of the dual loop have to detect a leak provided that no sensing element failure was detected during PBIT. If only one loop detects a leak than a Bleed Loop Fault message will be displayed on EICAS (300 seconds confirmation time).

Loop Arrangement for the Air Conditioning System

Loop Name Connected to IASC # Zone
1 Left Bleed IASC1 CH B Left Bleed
2 Right Bleed IASC1 CH B Right Bleed
3 Pack A IASC1 CH B Pack
4 Pack B IASC1 CH B Pack
5 Trim Air IASC1 CH B Trim Air

Troubleshooting:

CAS Message Logic

System Self-Test

Anti-ice and air conditioning bleed leak detection loop failure monitoring during PBIT (System Self-Test)

Failure case Color Code Resulting EICAS Message MDC Report and
Maintenance Procedure		 Pilot Action
One loop inner conductor open circuit CYAN BLEED LOOP FAULT YES
  1. Check continuity at each connector.
  2. Check continuity of each element inner conductor.
 Troubleshooting required before dispatch.
Both loops inner conductors open circuit. AMBER

AMBER

AMBER		 WING A/ICE LOOP FAIL
or
 L or R PYLON LOOP FAIL
or
 PACK LOOP FAIL
Dual Loop One loop short circuit CYAN BLEED LOOP FAULT YES
  1. Locate the short circuit using the leak event location function.
  2. Check for short circuit at the corresponding connector.
  3. Using the Tegam, check the Capacitance and Inductance between the inner and outer conductor of the corresponding loop. Reference nominal value in CMM 26- 14-47.
 Troubleshooting required before dispatch
Both loops short circuit AMBER

AMBER

AMBER		 WING A/ICE LOOP FAIL
or
 L or R PYLON LOOP FAIL
or
 PACK LOOP FAIL
Loop(s) outer conductor open circuit N/A Nothing
(Continuity of outer conductor not monitored)		 NO None
Single Loop Loop inner conductor open circuit AMBER

AMBER

AMBER		 TRIM AIR LOOP FAIL
or
 L BLEED LOOP FAIL
or
 R BLEED LOOP FAIL		 YES
  1. Check continuity at each connector.
  2. Check continuity of each element inner conductor.
 Troubleshooting required before dispatch.
Loop short circuit1 AMBER

AMBER

AMBER		 TRIM AIR LOOP FAIL
or
 L BLEED LOOP FAIL
or
 R BLEED LOOP FAIL		 YES
  1. Locate the short circuit using the leak event location function.
  2. Check for short circuit at the corresponding connector.
  3. Using the Tegam, check the Capacitance and Inductance between the inner and outer conductor of the corresponding loop. Reference nominal value in CMM 26-14-47.
 Troubleshooting required before dispatch
Loop outer conductor open circuit N/A Nothing
(Continuity of outer conductor not monitored).		 NO None

1 Inner conductor in short circuit with the outer conductor = inner conductor shorted to ground

20_zones_loops

loop_acs

Normal Operation

Anti-ice and air conditioning bleed leak detection loop failure monitoring during CBIT

Failure case Color Code Resulting EICAS Message MDC Report and
Maintenance Procedure		 Pilot Action
Dual Loop One loop inner conductor open circuit N/A Nothing
(Continuity of outer conductor not monitored)		 NO None
Both loops inner conductors open circuit.
One loop short circuit CYAN BLEED LOOP FAULT
after 300 sec.		 YES
  1. Locate the short circuit or leak using the leak event location function.
  2. Check for short circuit at the corresponding connector.
  3. Verify fouling condition on hot surface.
  4. Using the Tegam, check the Capacitance and Inductance between the inner and outer conductor of the corresponding loop. Reference nominal value in CMM 26-14-47.
 None
Monitoring still performed by the other loop.
Both loops short circuit or detecting heat RED

RED

RED		 WING ANTI-ICE LEAK
or
 PACK LEAK
or
 L or R PYLON BLEED LEAK		 Isolate the affected zone
Loop(s) outer conductor open circuit. N/A Nothing
(Continuity of outer conductor not monitored).		 NO None
Single Loop Loop inner conductor open circuit. N/A Nothing
(Continuity of inner conductor not monitored during CBIT).		 NO None
Loop short circuit or loop detecting heat RED

RED

RED		 TRIM AIR LEAK
or
 L BLEED LEAK
or
 R BLEED LEAK		 YES
  1. Locate the short circuit or leak using the leak event location function.
  2. Check for short circuit at the corresponding connector.
  3. Verify fouling condition on hot surface.
  4. Using the Tegam, check the Capacitance and Inductance between the inner and outer conductor of the corresponding loop. Reference nominal value in CMM 26-14-47.
 Isolate the affected zone.
Loop outer conductor open circuit. N/A Nothing
(Continuity of outer conductor not monitored).		 NO None

Open circuit = disconnect = break in continuity or when the resistance > (sum of all LDE resistances in series in the loop) * 2
Short-circuit = leak detected = inner conductor grounded

Leak event location function:

  • The outer conductor is grounded at several locations. Even if the outer conductor fails in open circuit, the leak detection and event location functions are still operational as long as the outer conductor is still grounded. This failure will never be detected.
  • If the inner conductor fails in open circuit, the leak detection function is still operational since the inner conductor is connected at both ends. However, the event location function will not provide the good location. The inner conductor failure will be indicated at the next PBIT.
  • When the % is above 100% or below 0%, that means the leak (or the short circuit) is close to one of the connectors but it is not possible to tell which one (a value above 100% does not necessary mean 100% and a value below 0% does not necessary mean 0%).

Figure 1 illustrates the leak location indication on aircraft with Service Bulletin 100-21-05 incorporated.

NOTE: The leak indication is in terms of W.S. or F.S. in order to ease troubleshooting.

To obtain the leak location in term of percentage on aircraft with Service Bulletin 100-21-05 incorporated reference the percentage to station tables.

post_leak_event_location

Fig. 1

Loop Detection Logic

Leak Sensing element is a coaxial cable. The controller monitors the insulation between the inner conductor and external conductor of this coaxial cable. To localize the short circuit the controller calculates the line resistance (or inner conductor resistance) from both sides.

IASC OPEN Circuit Detection

An Open Circuit is detected when the INNER conductor of a Loop element has lost continuity (infinite resistance). The IASC will consider a loop OPEN if the resistance of the loop is greater than a value defined in the chart.

Loop Value (Ohms)
LH & RH Bleed 75.0
LH & RH Pylon 14.0
LH & RH Fuse Wing 136.0
LH & RH Pylon Wing 136.0
Pack 26.0
Trim 62.0

NOTE: The open loop detection will not be performed if this loop has previously been detected grounded

IASC Short Circuit Detection

A short circuit is detected when the resistance between the inner conductor and the outer conductor (ground) is lower then 900 Ohms.

A SHORT Circuit is when the INNER conductor of a Loop element has continuity with its OUTER conductor (resistance below a certain threshold).

The IASC check for Bleed Leak Detection Loop SHORT Circuit in the following cases:

  • During PBIT (Power Up Bit) which is when power is applied to the IASC.
  • During IBIT (Initiated Bit) which is done by the user via the MDC IASC TEST function.

Short circuits are not monitored during the CBIT because the system is busy monitoring for leak.

In a dual loop system, if a SHORT is detected on one loop during PBIT, or IBIT, the MDC will report a "SHORT" and the IASC will display a BLEED LOOP FAULT (S) on the EICAS to indicate a loss of redundancy (one of the loop will be declared inoperative and ignored during the monitoring).

  • However, if both loops of the same system are detected SHORT during that same test, or if one loop is detected SHORT and the other loop is detected OPEN, the EICAS message will be L (R) PYLON LOOP FAIL, PACK LOOP FAIL or WING A/ICE LOOP FAIL depending of the system affected.

In that case, there will be two MDC messages created, one for each loop.

In a single loop system, if a SHORT is detected during PBIT or IBIT, the MDC will report a "SHORT" and the EICAS IASC will display a L (R) BLEED LOOP FAIL or TRIM AIR LOOP FAIL.

In that case, there will be one MDC messages created.

In the case of a SHORT Circuit, the IASC is able to determine which element of the loop is SHORT based on the insulation resistance.

In this case, the RUN EVENT LOC TEST function of the IASC will indicate at which location the SHORT has occurred.

Refer to section 2.3 (Troubleshooting of a SHORT Circuit) to make the correlation between the percentage provided by the IASC and the actual element involved.

If a SHORT happens during CBIT, the controller will consider a "LEAK". In the case of a dual loop system, the state of the second loop (Loop A or B) of that system will determine which EICAS message will be displayed.

If the second loop is also SHORT, the IASC will display the appropriate Warning message to indicate a Leak in the system.

If the second loop is OK, the IASC will display a BLEED LOOP FAULT message to indicate a loss of redundancy.

Troubleshooting Procedure for SHORT Circuit

Procedure

NOTE: When the MDC Fault is displayed, it indicates a connector identification number (e.g. MT144). THIS IDENTIFICATION NUMBER INDICATES ON WHICH LOOP THE FAULT WAS DETECTED. IT DOES NOT MEAN THAT THIS PARTICULAR CONNECTOR IS FAILED.

  • If the CAS Message is still present, perform a RUN EVENT LOC TEST of the IASC via the MDC.
  • If a SHORT Circuit is indicated on one of the Loop, note the location of it (in terms of total length percentage with IASC 92175A030300 or in terms of Fuselage Station or Wing Station with IASC 92175A030400).
  • Once the SHORTED element has been identified, disconnect it and measure the characteristics of the element with TEGAM 252 instrument and compare it with the nominal values provided in the CMM 26-14-47
  • If it is not good, replace the element.
  • If the Element resistance and isolation are correct, measure the isolation between each of the element connector center conductor and its outer shell. The resistance should be OPEN. If not, replace the connector.

Troubleshooting Procedure for OPEN Circuit

Procedure

NOTE: When the MDC Fault is displayed, it indicates a connector identification number (e.g. MT144). THIS IDENTIFICATION NUMBER INDICATES ON WHICH LOOP THE FAULT WAS DETECTED. IT DOES NOT MEAN THAT THIS PARTICULAR CONNECTOR IS FAILED.

  • With an analogue multimeter, locate the connector that is disconnected and fix the connection.
  • If all connector are OK, check for discontinuity within each element and replace the element.

Tooling

P/N Tool Name
TEGAM 252 / 253 or,
SINTERS 9240SI or
Equivalent		 LCR Meter
Loop Controller
Digital AC Multimeter/Ohmmeter.

Parts

P/N Part Description
Refer to
Fenwall CMM 26-14-47		 Bleed Leak Detection Loop Element
(as required)
Connector P/N Fenwal Connector (as required)
35491-0 Ceramic Insulator

Bleed Leak Event Location in term of percentage

NOTE: To obtain a percentage from a W.S. or a F.S, use the data presented below. Intermediate values can be interpolated linearly.

Leak Event Pylon Loops

Bleed leak detection loop common to the ACS and AIPS:

LH PYLON LOOP
Reporting LRU: IASC 1
Total Loop Length: 35 inches
MDC Identification: MT063
Zero Point: Connector number MT63P2 in the LH Pylon
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From FS 740

MT63 Aft Equip Bay, between the 2 HP ducts (air conditioning & anti-ice ducts) near the engine interface.
  FS 748 50 17.5  
To FS 734 100 35 Aft Equip Bay, beside the HPV

RH PYLON LOOP
Reporting LRU: IASC 2
Total Loop Length: 36 inches
MDC Identification: MT044
Zero Point: Connector number MT44P2 in the RH Pylon
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From FS 740

MT44 Aft Equip Bay, between the 2 HP ducts (air conditioning & anti-ice ducts) near the engine interface.
  FS 748 50 15.5  
To FS 734 100 31 Aft Equip Bay, beside the HPV

Leak Event Pylon/Wing Loops

Bleed leak detection loop for the AIPS:

LH PYLON/WING LOOP
Reporting LRU: IASC 2
Total Loop Length: 741 inches
MDC Identification: MT045
Zero Point: Connector number MT119P2 at the LH Wing Tip
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From WS 356

MT119 Outboard wing (from the access panel located at wing tip to the access panel located at W.S. 262)
To WS 262 15 108
From WS 262 15 108 MT103 Mid wing (between the 2 access panels located at W.S. 262 and W.S. 151)
To WS 151 32 237
From WS 151 32 237 MT 51 Inboard wing (from the access panel located at W.S. 151 to the access panel located at wing root)
To WS 43 49 362
From WS 43 49 362 MT 49 Wing root at leading edge level
  FS 555 60 444 Above the wing
To FS 635 71 526 Just Aft of wheel well (just Fwd of the baggage door)
From FS 635 71 526 MT 47
  FS 692 80 588 Aft belly fairing, crossover duct located between the skin and the fairing up to the skin interface.
To FS 699 88 650
From FS 699 88 650 MT 45 Skin interface at the bottom of the Aft equipment bay
  FS 724 94 694 Anti-ice duct in the Aft equipment bay
To FS 740 100 738 Aft Equip Bay, between the 2 HP ducts (air conditioning & anti-ice ducts) near the engine interface.
RH PYLON/WING LOOP
Reporting LRU: IASC 1
Total Loop Length: 735 inches
MDC Identification: MT054
Zero Point: Connector number MT118P2 at RH Wing Tip
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From WS 356

MT118 Outboard wing (from the access panel located at wing tip to the access panel located at W.S. 262)
To WS 262 15 108
From WS 262 15 108 MT42 Mid wing (between the 2 access panels located at W.S. 262 and W.S. 151)
To WS 151 33 237
From WS 151 33 237 MT 60 Inboard wing (from the access panel located at W.S. 151 to the access panel located at wing root)
To WS 43 50 362
From WS 43 50 362 MT 58 Wing root at leading edge level
  FS 555 61 444 Above the wing
To FS 635 72 526 Just Aft of wheel well (just Fwd of the baggage door)
From FS 635 72 526 MT 56
  FS 692 81 588 Aft belly fairing, crossover duct located between the skin and the fairing up to the skin interface.
To FS 699 89 650
From FS 699 89 650 MT 54 Skin interface at the bottom of the Aft equipment bay
  FS 724 95 689.5 Anti-ice duct in the Aft equipment bay
To FS 740 100 729 Aft Equip Bay, between the 2 HP ducts (air conditioning & anti-ice ducts) near the engine interface.
LH FUSE/WING LOOP
Reporting LRU: IASC 1
Total Loop Length: 726 inches
MDC Identification: MT053
Zero Point: Connector number MT117P1 at the LH Wing Tip
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From WS 356

MT117 Outboard wing (from the access panel located at wing tip to the access panel located at W.S. 262)
To WS 262 15 108
From WS 262 15 108 MT65 Mid wing (between the 2 access panels located at W.S. 262 and W.S. 151)
To WS 151 33 237
From WS 151 33 237 MT 59 Inboard wing (from the access panel located at W.S. 151 to the access panel located at wing root)
To WS 43 50 362
From WS 43 50 362 MT 57 Wing root at leading edge level
  FS 555 61 444 Above the wing
To FS 635 72 526 Just Aft of wheel well (just Fwd of the baggage door)
From FS 635 73 526 MT 55
  FS 635 73 526 Aft belly fairing, crossover duct located between the skin and the fairing up to the skin interface.
To FS 692 82 592.5
From FS 699 92 659 MT 53 Skin interface at the bottom of the Aft equipment bay
  FS 724 96 689.5 Anti-ice duct in the Aft equipment bay
To FS 734 100 720 Aft Equip Bay, beside the HPV
RH FUSE/WING LOOP
Reporting LRU: IASC 2
Total Loop Length: 715 inches
MDC Identification: MT046
Zero Point: Connector number MT120P1 at the RH Wing Tip
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From WS 356

MT120 Outboard wing (from the access panel located at wing tip to the access panel located at W.S. 262)
To WS 262 15 108
From WS 262 15 108 MT104 Mid wing (between the 2 access panels located at W.S. 262 and W.S. 151)
To WS 151 33 237
From WS 151 33 237 MT 52 Inboard wing (from the access panel located at W.S. 151 to the access panel located at wing root)
To WS 43 51 362
From WS 43 51 362 MT 50 Wing root at leading edge level
  FS 555 444 444 Above the wing
To FS 635 74 526 Just Aft of wheel well (just Fwd of the baggage door)
From FS 635 74 526 MT 48
  FS 692 83 588 Aft belly fairing, crossover duct located between the skin and the fairing up to the skin interface.
To FS 699 92 650
From FS 699 92 650 MT 46 Skin interface at the bottom of the Aft equipment bay
  FS 724 96 679.5 Anti-ice duct in the Aft equipment bay
To FS 734 100 709 Aft Equip Bay, beside the HPV

Leak event Bleed/Trim Air/Pack loops

Bleed leak detection loop for the ACS:

LH BLEED LOOP
Reporting LRU: IASC 1
Total Loop Length: 111 inches
MDC Identification: MT067
Zero Point: Connector number MT67P2 in the LH pylon at the Air Turbine Starter duct interface with the engine.
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From FS 699

MT 67 ATS interface with the engine at the pylon
To FS 746 100 109 Just beside the lower FCV
RH BLEED LOOP
Reporting LRU: IASC 2
Total Loop Length: 419 inches
MDC Identification: MT038
Zero Point: Connector number MT71P2 at the APU firewall.
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From FS 857

MT71 APU firewall
  FS 834 15 60.5  
To FS 817 30 121 Ground air duct connection
From FS 817 30 121 MT40 T connection between the APU duct and the ground air duct
  FS 758 49 198  
To FS 699 68 275 ATS interface with the engine at the pylon
From FS 717 68 275 MT38 Crossover duct T junction on the RHS
  FS 717 84 339 Crossover duct T junction on the LHS
To FS 750 100 403 Just beside the upper FCV

NOTE: The 3 elements of the RH bleed loop are interconnected by an electrical harness

TRIM AIR LOOP
Reporting LRU: IASC 2
Total Loop Length: 358 inches
MDC Identification: MT036
Zero Point: Connector number MT124P2 under the baggage bay floor.
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From FS 660

MT124 Connector located under the baggage bay
  FS 657 6 20.5  
To FS 669 12 41 AFT pressure bulkhead interface under the baggage bay
From FS 669 12 41 MT69 AFT pressure bulkhead interface in the AFT equipment bay
  FS 707 27 95.5  
To FS 756 42 150 Trim air duct just AFT of the access door
From FS 756 42 150 MT36
To FS 81 6 70 250 Below the pre-cooler on the floor structure
From FS 81 6 70 250 MT 61 Pre-cooler outlet header
  FS 780 85 303  
To FS 756 100 356 Just downstream of upper FCV

NOTE: 3 elements of the trim loop are connected together and the fourth one (MT061) is interconnected with the 3 others by an electrical harness.

PACK LOOP A
Reporting LRU: IASC 1
Total Loop Length: 171 inches
MDC Identification: MT073
Zero Point: Connector number MT73P2 under the pre-cooler.
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From FS 816

MT 73 Under the pre-cooler
  FS 804 50 85.5  
To FS 765 100 171 Just downstream of lower FCV
PACK LOOP B
Reporting LRU: IASC 2
Total Loop Length: 176 inches
MDC Identification: MT141
Zero Point: Connector number MT141P1 under the pre-cooler.
Limit
(of each element)		 Fuselage Station Percentage
Reported by MDC		 Distance from
Zero Point (inches)		 Element Detail
From FS 816

MT141 Under the pre-cooler
  FS 804 50 88  
To FS 765 100 176 Just downstream of lower FCV
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