For the complete Troubleshooting Guide, please refere to the following link: Troubleshooting Guide for Bleed Loops

Page Contents

• Abbreviation Guide
• System Description
• Loops Arrangement for the AIPS and Pylon
• Loops Arrangement for the Air Conditioning System

ACS	Air Conditioning System
AIPS	Airframe Ice Protection System
APU	Auxiliary Power Unit
ATS	Air Turbine Starter
CBIT	Continuous Built-In Test
CBW	Wing Cross Bleed Valve
CH	Channel
Element	Hot Air Leak Detection Sensor with a connector on each end
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	Assy 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

The alarm temperatures are as follows:

 

• 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).

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
Dual Loop	One loop inner conductor open circuit	CYAN	BLEED LOOP FAULT	YES Check continuity at each connector. 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
	One loop short circuit	CYAN	BLEED LOOP FAULT	YES Locate the short circuit using the leak event location function. Check for short circuit at the corresponding connector. 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 Check continuity at each connector. Check continuity of each element inner conductor.	Troubleshooting required before dispatch.
	Loop short circuit *	AMBER AMBER AMBER	TRIM AIR LOOP FAIL  or L BLEED LOOP FAIL  or R BLEED LOOP FAIL	YES Locate the short circuit using the leak event location function. Check for short circuit at the corresponding connector. 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

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

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 Locate the short circuit or leak using the leak event location function. Check for short circuit at the corresponding connector. Verify fouling condition on hot surface. 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 Locate the short circuit or leak using the leak event location function. Check for short circuit at the corresponding connector. Verify fouling condition on hot surface. 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.

For IASC P/N 92175A030300 only, when the % is above 100% or below 0%, that means that the leak (or the short circuit) is close to one of the connector 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%).

The figure below in the guide show how the leak location is indicated on aircraft 20001 to 20100 and for aircraft Pre SB 100-21-05.

On aircraft 20101 and subs or aircraft with Service Bulletin 100-21-05 incorporated, the leak location is indicated in terms of Wing Station or Fuselage Station in order to ease troubleshooting. To obtain the leak location in term of percentage on aircraft 20101 and subs or in aircraft with Service Bulletin 100-21-05 incorporated, see section Bleed Leak Event Location in terms of Percentage.

From aircarft 20291 and subs or in aircraft with SB100-21-10 the location is given in Wing / Fuselage Station and percentage.

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.

1. 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	Triggering 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.

2. IASC Short Circuit Detection

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.

1. If the CAS Message is still present, perform a RUN EVENT LOC TEST of the IASC via the MDC.
2. 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).
3. 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
4. If it is not good, replace the element.
5. If the Element resistance and isolation are correct, measure the isolation between each of the element connector centre conductor and its outer shell. The resistance should be OPEN. If not, replace the connector.

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.

1. Disconnect P4 of the IASC #1 or #2 (it depends where the loop is connected, see the schematics to find out the controller)
2. With an analogue multimeter, check the resistance of the respective pins. If there is higher resistance than described in section 1 IASC OPEN Circuit Detection locate the connector that is disconnected and fix the connection.
3. If all connector are OK, check for discontinuity within each element and replace the element.

P/N	TOOL NAME	Range	Tolerance
BK 879B or TEGAM 252 / 253 or, SINTERS 9240SI or Equivalent	LCR Meter Loop Controller Digital AC Multimeter/Ohmmeter	1 kHz test frequency 0.6-1.0 Vrms test level 0 VDC 0-40 kΩ Z impedance 32-104°F (0-40 °C) operate temp	±5% Not applicable ±0.02 VDC ±5% Not applicable

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

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

Message EICAS

• L PYLON LOOP FAIL (Pre SB 100-34-18)
• L PYLON LOOP FAIL (Post SB 100-34-18)

MDC Fault code: 

• B3-007092 – L PYLON SHORT CIRCUIT
• B3-007090 – L PYLON OPEN CIRCUIT

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:	31 inches (36 inches for aircraft 20156 and subs)
MDC Identification:	MT044
Zero Point:	Connector number MT44P2 in the RH Pylon

Message EICAS

• R PYLON LOOP FAIL (Pre SB 100-34-18)
• R PYLON LOOP FAIL (Post SB 100-34-18)

MDC Fault code:

• B3-007771 – R PYLON SHORT CIRCUIT
• B3-007772 – R PYLON OPEN CIRCUIT

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

Bleed leak detection loop common to the AIPS:

LH PYLON/WING LOOP
Reporting LRU:	IASC 2
Total Loop Length:	738 inches (741 inches for aircraft 20156 and subs)
MDC Identification:	MT045
Zero Point:	Connector number MT119P2 at the LH Wing Tip

Message EICAS

• WING A/ICE LOOP FAIL (Pre SB 100-34-18)
• WING A/ICE LOOP FAIL (Post SB 100-34-18) or BLEED LOOP FAULT

MDC Fault code:

• B3-008099 – L PYLN / WING LOOP SHORT CIRCUIT
• B3-008100 – L PYLN / WING LOOP OPEN CIRCUIT 

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	MT51	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	MT49	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	MT47
	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	MT45	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:	729 inches (735 inches for aircraft 20156 and subs)
MDC Identification:	MT054
Zero Point:	Connector number MT118P2 at RH Wing Tip

Message EICAS

• WING A/ICE LOOP FAIL (Pre SB 100-34-18)
• WING A/ICE LOOP FAIL (Post SB 100-34-18) or BLEED LOOP FAULT

MDC Fault code:

• B3-008105 – R PYLN / WING LOOP SHORT CIRCUIT
• B3-008106 – R PYLN / WING LOOP OPEN CIRCUIT

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	MT60	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	MT58	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	MT56
	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	MT54	Skin interface at the bottom of the aft equipment bay
	FS 724	95	689.5		Anti-ice duct in the qft 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:	720 inches (726 inches for aircraft 20156 and subs)
MDC Identification:	MT053
Zero Point:	Connector number MT117P1 at the LH Wing Tip

Message EICAS

• WING A/ICE LOOP FAIL (Pre SB 100-34-18)
• WING A/ICE LOOP FAIL (Post SB 100-34-18) or BLEED LOOP FAULT

MDC Fault code:

• B3-008101 – L FUSE / WING LOOP SHORT CIRCUIT
• B3-008102 – L FUSE / WING LOOP OPEN CIRCUIT

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	MT59	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	MT57	Wing root at leading edge level
	FS 555	62	444		Above the wing
To	FS 635	73	526		Just aft of wheel well (just Fwd of the baggage door)
From	FS 635	73	526	MT55
	FS 692	82	592.5		Aft belly fairing, crossover duct located between the skin and the fairing up to the skin interface.
To	FS 699	92	659
From	FS 699	92	659	MT53	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:	709 inches (715 inches for aircraft 20156 and subs)
MDC Identification:	MT046
Zero Point:	Connector number MT120P1 at the RH Wing Tip

Message EICAS

• WING A/ICE LOOP FAIL (Pre SB 100-34-18)
• WING A/ICE LOOP FAIL (Post SB 100-34-18) or BLEED LOOP FAULT

MDC Fault code:

• B3-008103 – R FUSE / WING LOOP SHORT CIRCUIT
• B3-008104 – R FUSE / WING LOOP OPEN CIRCUIT

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	MT52	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	MT50	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	MT48
	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	MT46	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

Bleed leak detection loop for the ACS:

LH BLEED LOOP
Reporting LRU:	IASC 1
Total Loop Length:	109 inches (111 inches for aircraft 20156 and subs)
MDC Identification:	MT067
Zero Point:	Connector number MT67P2 in the LH pylon at the Air Turbine Starter duct interface with the engine.

Message EICAS

• L BLEED LOOP FAIL

MDC Fault code:

• B3-007008 – L BLEED LOOP SHORT CIRCUIT
• B3-007009 – L BLEED LOOP OPEN CIRCUIT

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:	403 inches (419 inches for aircraft 20156 and subs)
MDC Identification:	MT038
Zero Point:	Connector number MT71P2 at the APU firewall.

Message EICAS

• R BLEED LOOP FAIL

MDC Fault code:

• B3-007008 – R BLEED LOOP SHORT CIRCUIT
• B3-007009 – R BLEED LOOP OPEN CIRCUIT

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:	356 inches (358 inches for aircraft 20156 and subs)
MDC Identification:	MT036
Zero Point:	Connector number MT124P2 under the baggage bay floor.

Message EICAS

• TRIM AIR LOOP FAIL

MDC Fault code: 

• B3-008034 – TRIM AIR LOOP SHORT CIRCUIT
• B3-008035 – TRIM AIR LOOP OPEN CIRCUIT

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	MT61	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:	176 inches
MDC Identification:	MT073
Zero Point:	Connector number MT73P2 under the pre-cooler.

Message EICAS 

• PACK LOOP FAIL
• BLEED LOOP FAULT

MDC Fault code: 

• B3-007407 – PACK LOOP A SHORT CIRCUIT
• B3-007408 – PACK LOOP A OPEN CIRCUIT 

Limit (of each element)	Fuselage Station	Percentage Reported by MDC	Distance from Zero Point (inches)	Element	Detail
From	FS 816			MT73	Under the pre-cooler
	FS 804	50	85.5
To	FS 765	100	176		Just downstream of lower FCV

PACK LOOP B
Reporting LRU:	IASC 2
Total Loop Length:	171 inches
MDC Identification:	MT141
Zero Point:	Connector number MT141P1 under the pre-cooler.

Message EICAS

• PACK LOOP FAIL
• BLEED LOOP FAULT

MDC Fault code: 

• B3-008031 – PACK LOOP B SHORT CIRCUIT
• B3-008032 – PACK LOOP B OPEN CIRCUIT 

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	171		Just downstream of lower FCV