REFERENCE 24-032/MSG-387 — Page 1
ELECTRICAL POWER
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-001
IDG
761574B
Collins Aerospace
737
24
UAL
The B737 IDGs have been unable to meet turnaround times in the shop due to parts shortages of the main rotor
bearing, PN 5913156. This shortage has severely impacting 737 operations. United has altered the maintenance
intervals and the shop level component build standard to limit the number of scheduled IDG and rotor removals until
we are clear of the shortages. This issue appears to be present at both OEM and third-party repair shops with either
OEM or PMA bearings.


Have other operators been impacted by this parts shortage, and what changes have you made to limit the
impact?
What efforts/policies have Collins or other repair facilities put in place to make sure we do not see parts
shortages of critical components in the future?
Other Airlines, Operators, OEMs, and suppliers, please discuss.
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-002
A220 Batteries
Depleted Due to Tow
PWR Switch Left to On
C06420300-017
FOKKER
A220
24-41
AFR
ELECTRICAL/TOWING
SERVICE PANEL
Since A220 entry into service, numerous batteries have been removed for low voltage inducing delays
and flight cancellations.
Although towing on bat is not used on AFR fleet, aircraft inspection revealed tow power switch was set
and let to ON, If tow pwr switch is let to ON with no power on aircraft, nav lights, brakes and other
elements are still energized by batteries. And they discharge.
One enhancement could be a redesign of the electrical towing service panel with a guard on tow PWR
switch.
Q1) For other operators, AF would appreciate feedback on this topic:
 Did you suffer any similar events?
 How do you manage the mishandling of the tow PWR switch (technical note, airline comment,
label flag on panel, etc.)?
Q2) For OEM and A/C manufacturers:
 Do you have any feedback and scheduling about the tow PWR switch guard enhancement?
 Are there any other modifications (software) to limit/inhibit batteries depletion?
Other Airlines, Operators, OEMs, suppliers, please discuss.
REFERENCE 24-032/MSG-387 — Page 2
ELECTRICAL POWER
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-003
VFSG Disconnect
Inoperative Issue
7001330H04
Collins
787-9
24
KAL
Variable Frequency
Starter Generator
Boeing
1. Background
 Korean Air experienced 3 times aircraft delays because of an inoperative VFSG disconnect function.
 First case, the inoperative disconnect function was not regenerated during the shop visit.
 But in the other 2 cases, the root cause was a disconnected solenoid. Collins found that the disconnect
solenoid pushrod stuck
2. Request
 Please share other operators' experience.
 To collect similar cases and perform detailed investigation.
 To provide the solution to prevent the inoperative disconnect function because of Disconnect Solenoid
Pushrod Stuck
Other Airlines, Operators, OEMs, suppliers, please discuss.
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-004
Practical Shop Level
Trainings
7001330 VFSG
Collins
787
24
KAL
7000021 ASG
1. Background

KAL Requested VFSG/ASG shop level training from Collins. When KAL tried to contact Collins regarding
practical shop level training, Collins offered 3 options below:
o Option 1: Collins' instructor comes to KAL facility (practical training_7 days chargeable)
o Option 2: KAL's staff to go to Collins Windsor Locks (theoretical training_1.5 days)
o Option 3: On-line Training
2. Request


Please provide the appropriate training that KAL desires for Collins’ component.
KAL's staff to go to a Collins shop for practical shop level training (5~7 days).
o Trainee: Engineer, Technician, Inspector (4 personnels)
o Course: Disassembly, Cleaning, Inspection/Repair, Assembly and Testing.
Other Airlines, Operators, OEMs, suppliers, please discuss.
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-005
EBPSU Failure Root
Cause Investigation
C3805-901 EBPSU
Thales
787
24
ANA
Safran
REFERENCE 24-032/MSG-387 — Page 3
ELECTRICAL POWER
EBPSU failure root cause investigation
Recently ANA faced an increasing number of cases where EBPSUs removed due to flight delays caused by EBPSU
messages have been found to be defective at the THALES repair shop. Flight delays occurred only one case in
2022, but at least 6 cases have already occurred in 2023.
All of these 6 EBPSUs failed test at “Soft Start” and were exchanged with another unit due to BER (Beyond
Economic Repair) of eBrake CNVTR Assy.
It means that Thales repair shop does not usually identify defects at sub-component level (e,g,, capacitor, resistor
etc.) for EBPSU that failed in testing. Thales/Safran implied high investigation fee will be charged when ANA
requested root cause investigation.
This is different from the situation described in 787-FTD-24-20001, where there are many nuisance messages.
The FIM revision in 2021 is having an effect, and the number of cases of flight delays due to nuisance messages is
decreasing, whereas flight delays due to EBPSU failures are increasing more than ever.
ANA believes Thales/Safran should take responsibility for root cause investigation to improve EBPSU reliability even
if BER.
On the other hand, there are still certain number of NFF shop finding results (At least 7ea in 2023). ANA is especially
concerned about short time and zero-time removals shop findings.

From Jan.1 to Dec.31 2023
o Total removal: 22ea /
o Short time* removal: 4ea (*Short time: Under 1,000 FH since return from Thales)/
o Zero-time removal: 3ea
ANA found some specific serial numbers tend to repeatedly be removed in short time or zero time.
All zero-time removal EBPSUs previous removal time were short time or zero time and shop findings were NFF.
Warranty was not applied to those EBPSU and if we request internal visual inspection or some additional testing,
Thales will charge high investigation fee.



Request 1: ANA would like Boeing/Thales/Safran to perform the root cause investigation of EBPSU failure.
Request 2: ANA would like to request Boeing/Thales/Safran to provide corrective actions to the EBPSU
failure upon root cause identification.
Request 3: ANA would like to request Thales/Safran to review and improve support policy for specific
EBPSUs are repeatedly removed in short time.
Other Airlines, Operators, OEMs, suppliers, please discuss.
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-006
ISPS 1191-46
Reliability Problems
ISPS 1191-46
Astronics
A320
25-21
TAP
As known by ASTRONICS, TAP has faced low reliability of the ISPS 1191-46 since these units were first installed in
the fleet. After going through a campaign to modify to the latest standard (Mod E), the reliability issue remained. The
latest improvement to the unit made by ASTRONICS is by using more robust and reliable components during the
repairs.
ASTRONICS claims that this highly increases the unit’s reliability, but is too soon to confirm by TAP’s experience.
Our main concern is that this improvement is being done at a repair level and without any Service Bulletin
associated, which makes it difficult to identify which units have the “new” components. In our view, this should be
REFERENCE 24-032/MSG-387 — Page 4
ELECTRICAL POWER
done via a Service Bulletin, The reliability improvement is definite, ASTRONICS should provide operators with the
means necessary to apply this modification themselves on a proactive basis. This would help operators to modify
the units before they fail during operation and without having to suffer the impact of the unscheduled removal, which
directly impacts the passenger experience during the flight.
Can ASTRONICS translate this modification to an SB and provide the means necessary for the operator to
implement it to its own units? Other Operators and ASTRONICS comments, please.
Other Airlines, Operators, OEMs, and suppliers, please discuss.
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-007
Wire Harness
Assemblies’ Changes
Between BCU and
Main/APU Battery SB
Justification
673Z4050-XX
Boeing
787
24-31
KLM
673Z4016-XXXX
673Z3018-XXXX
673Z3011-XXXX
Thales
Main BAT CHGR: 673Z4050-XX
APU BAT CHGR: 673Z4016-XXXX
Main BAT: 673Z3018-XXXX
APU BAT: 673Z3011-XXXX
Since the two incidents on the APU battery in 2013, Boeing changed the original design of the Main and APU
Battery. It added a Battery Enclosure with a Venting System. The design change/addition had consequences, direct
and in-direct such as:
Direct:
 Extra weight
 Added MPD task for the Burst Disk Inspection of the Enclosure
 The duration of the Battery Capacity Test became much longer. (minimum 2 hrs extra to remove/install
multiple bolts of the enclosure access door, which result in extra maintenance burden)
 And the execution of the Battery Capacity Test became more complex.
In-direct:
 More prone to mistakes during the capacity test which lead to over discharged batteries.
 Added workload for Engineering to research the issue, improve the AMM Procedures, and creating
awareness for maintenance personnel.
Due to these consequences operator KLM experienced in the past 8 years higher ground time, increase prone to
mistakes during maintenance, and longer of period where the electrical power is removed from the a/c.
Eventually 2 Service Bulletins were needed to solve these issues:
 SB240074 for Cell balancing (implemented).
 SB240092 to change the Wire Harness assemblies’ between BCU Main/APU Battery (published
22/aug/2023), that will provide signal pathways needed for testing with Ground Support Equipment (GSE)
without having to open the enclosure and remove the battery from the battery enclosure.
However, in KLM’s initial cost calculation for SB240092, the payback time is greater than the lifespan of the aircraft.
While implementing SB240092 gives benefits such as reduced ground time, flexibility in planning, reduce period of
the electrical power is removed from the aircraft, no material usages, and less prone to mistakes during
maintenance.
REFERENCE 24-032/MSG-387 — Page 5
ELECTRICAL POWER
In KLM’s opinion, this SB is not a modification but rather a correction of the changed original design of the Main and
APU Battery. Therefore, Boeing should at least reimburse the material cost and/or the manhour cost.
Other Airlines, Operators, OEMs, suppliers, regulatory please discuss.
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-008
Static Inverter
Obsolete CMM
1-002-0102-2089
Avionic
Instruments
737NG
24-34
THY
1-002-0102-2090
777
The static inverter P/N: 1-002-0102-2090 has been obsolete according to Avionic Instruments Service Information
Letter 1-002-0102-2170-24-49. Currently, static inverter P/N: 1-002-0102-2090 continues to be used in our fleet. In
addition, as Turkish Airlines, our workshop has the repair capability for this inverter and the unserviceable static
inverters P/N: 1-002-0102-2090 are repaired according to CMM 24-21-01.
However, according to the latest e-mail from the Avionic Instruments, it was stated that the static inverters (P/N: 1002-0102-2089 and P/N: 1-002-0102-2090) are no longer repairable because the CMM is also obsolete.
The information that CMM will not be updated is included in Avionic Instruments Service Information Letter 1-0020102-2170-24-49, but there is no information in this publication that CMM is obsolete. As THY, this is the first time
we see that the CMM of an actively used part is obsolete.


Q1. Unless there is an airworthiness violation, can a decision be made that a part in active use can no
longer be repaired or that the CMM is obsolete?
Q2. If the CMM is no longer available, shouldn't operators be informed about this issue by Boeing or Avionic
Instruments?
Other Airlines, Operators, OEMs, suppliers, please discuss.
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-009
IDG A330 Test
Requirements
752168
Collins
A330
24
LHT
755017
LHT has experienced a high failure rate while testing A330 IDGs on the test
stand. Most failures are related to the frequency regulation test, especially for
overhauled units. The IDG runs with a maximum speed and load for 60
seconds, and it usually overheats causing heavy wear in the motor pump
assy and in the carrier shaft (see Figure 1).
LHT tested an overhauled unit from the OEM in accordance with the CMM
24-11-82 test section in detail the frequency regulation check (step 9) and
the unit failed on the test stand as well.
Collins has adjusted many test parameters lately, which has improved the
output of the load transient check, but we are still waiting for an update in the frequency regulation check (step 9).


Are other airlines/operators running into similar issues? Please comment.
LHT requests Collins to revise the frequency regulation check for overhauled units in CMM 24-11-82.
Other Airlines, Operators, OEMs, suppliers, regulatory please discuss.
REFERENCE 24-032/MSG-387 — Page 6
ELECTRICAL POWER
ITEM
SUMMARY TITLE
24-010
Load Shedding Issue
LRU PN
VENDOR
AIRCRAFT
AIRBUS
A350
ATA
FROM
THY
We encounter load shedding issue on our A350 aircrafts since 2021. When the operations with high electrical load
such as cargo loading, tests on cockpit etc. are done concurrently, electrical load shedding occurs and too many IFE
monitors get de-energized. This issue has been causing operational delays.
In order to prevent load shedding, we turn on the APU while performing the operations which need high electrical
load. In case of load shedding occurrence, we perform Pax SYS reset from the cockpit. THY considers that this
procedure puts a huge burden on operation and maintenance side. To find an alternative solution and fix the
problem THY contacted to Airbus via Techrequest 81247607.
To briefly summarize, after some conversation and report sharing, Airbus declared that the Load shedding problem
on A350 aircraft were also reported from other operations and an internal investigation would be launched to fix and
review the issue. Additionally, an alternative interim action was provided to THY until the permanent solution. As per
Airbus’ recommendation, THY set OFF the ELM P/B just after energizing aircraft and set it ON position again just
before engine start.
THY Flight OPS team also contacted Airbus in order to clarify the use of ELM P/B and got confirmation/verification
from Airbus via Techrequest 81299288. By implementing this action, delays caused by load shedding problem have
significantly reduced. However, we still face same problem from time to time.
We are aware of the Airbus internal investigation is not going to be finalized in a short time, but we need a
permanent fix of the problem as soon as possible.
Other Airlines, Operators, OEMs, suppliers, please discuss.
ITEM
SUMMARY TITLE
LRU PN
VENDOR
AIRCRAFT
ATA
FROM
24-011
Obsolete Parts
28B545-9
APU Starter/Generator
Honeywell
737
24
KLM
Honeywell CMM 24-21-14, Revision 8 currently calls for the following three types of tubing that are unknown on the
commercial market:
1. HST2230125-003 - Unknown on commercial market, Unknown on Honeywell portal.
2. HST2330126-001 - Unknown on commercial market, known on Honeywell portal.
3. HST2333126-016 - Unknown on commercial market, known on Honeywell portal.
Two of these are known on the Honeywell portal, and quotes were requested. The official response from Honeywell
was, “Honeywell has determined that this is an obsolete part and we respectfully no bid as we do not have the
capability to produce this part. Please consider this a formal No Bid for your request.”
Could Honeywell please provide technical specifications (Material Type, Wall Thickness, Min/Max Inner & Outer
diameters) for these three proprietary part numbers so that we can identify an equivalent tubing that is available on
the commercial market?
Other Airlines, Operators, OEMs, suppliers please discuss.