EIS2 - Multiple ECAM alerts due to DMC
behaviour
Reference: 31.63.00.005 First Issue Date: 24-SEP-2009 Last Publication Date:
10-MAR-2015 Status: Closed
ATA: 00-00 ; 31-63 A/C Type : A320
Affected Part Number: SXT3DE2SA0700 Supplier : THALES AVIONICS SA
Potential Impact: Operational Reliability ; Line Maintenance ; Airworthiness
Linked Documentation: SB 31-1335 ; SB 31-1359 ; SB 31-1372
Engineering Support
First Issue Date: 24-SEP-2009 Last Publication Date: 10-MAR-2015 Status:
Closed
Issue Description
Two operators reported several flight diversions on A320 family aircraft
after multiple ECAM alerts were intermittently triggered associated with
some red flags on PFD & ND of one side. Most of the ECAM alerts were
related to engine parameter overlimit or discrepancy (N1, N2, EGT, FF)
even though no overlimits or faults were noticed on engine parameter
indications on EWD. The ECAM alerts were always transitory (less than a
few seconds) but most of them could be triggered again afterwards.
Consequence
Considering the discrepancy between the engine parameters on EWD and
the ECAM alerts, flight crews elected to divert the flight without other
actions.
Airbus also received a few reports from other operators with similar
symptoms. But in these cases, the ECAM alerts immediately stopped and
EFIS indications were recovered after flight crew switched the Display
Management computer (DMC) of affected side on DMC#3 position. There
were no other occurrences and aircraft landed uneventful at expected
destination.
Investigation Status
The analysis of retrieved data shows that the origin of events was an
unexpected behavior of one DMC (DMC#1 or DMC#2). The investigation
performed by Airbus and Thales Avionics shows that one DMC may
randomly send erroneous parameters on its ARINC 429 output bus. As
both Flight Warning Computers (FWC) use DMC output data to detect and
trigger some alerts, they may spuriously detect and intermittently trigger
one or several alerts among the following list:
- ENG 1(2) N1(N2)(EGT)(FF) OVER LIMIT
- ENG 1(2) N1(N2)(EGT)(EPR)(FF) DISCREPANCY
- NAV ATT(ALTI)(HDG) DISCREPANCY
- NAV FM/GPS POS DISAGREE
- FUEL F.USED/FOB DISAGREE
- MINIMUM or HUNDRED ABOVE callouts
In addition, the affected DMC may flag some EFIS parameters on PFD &
ND of associated side. The investigation shows that in such a case, ECAM
alerts and EFIS flags are spurious and do not refer to any real aircraft
system failures. It is also confirmed that engine parameter indications,
which are displayed on the upper part of EWD, remain correct during
flight, as noticed by operators.
Despite the intensive campaign led by Thales Avionics, the origin of DMC
misbehavior is still not fully identified. However, Thales highly suspects a
corruption of the Static Random Access Memory (SRAM) on DMC
input/output (I/O) cards. They reproduced in lab the same aircraft
symptoms by corrupting the SRAM. In addition, it has been shown that
the phenomenon disappears after a DMC reset. That is fully in accordance
with operator reports, which state that ECAM alerts and EFIS flags were
cleared after a DMC reset performed by their maintenance teams.
Mitigation / Interim Plan
A new monitoring of the DMC I/O SRAM integrity has been introduced in
EIS2 S8-2 software (PN SXT30-E2SA-0820, MOD 38146). In case of SRAM
corruption, the affected DMC loads again the SRAM three times maximum
and finally performs an autoreset whether it remains corrupted. During
the DMC re-initialisation for about 10 seconds, the amber message
"INVALID DATA" is displayed on associated LCDUs.
This protection should avoid the triggering of spurious ECAM alerts and
EFIS flags reported by several operators. This monitoring is automatically
activated as soon as the software S8-2 or successive is installed. The
efficiency of this modification has been tested during 18 months on
several selected in-service aircraft. One case has been identified and
analyzed by Airbus and Thales. This case confirmed the efficiency of the
fix.
Maintenance Information
On aircraft without EIS2 S8-2 software, if the defect is present on ground,
Airbus recommends to identify the involved DMC, to reset it and to
confirm the defect disappears. It is then requested to monitor closely this
DMC during next flights and to remove it in case of multiple reoccurrence.
Please follow the new TSM task 31-63-82-810-853.
Repercussion on A/C Dispatch
MMEL Temporary Revisions (TR) N°01-31/01M, 01-31/02M and 01-
31/03M have been dispatched to cover this issue.
Solution
SRAM monitoring function has been introduced since EIS2 S8-2 software
and subsequent. It is available without specific activation condition as
soon as the EIS2 software is installed. At the time of the closure of this
TFU, in-service EIS2 software with the new function are S8-2, S9 (PN
SXT42-E2SA-090A, MOD 151097) and S9E (PN SXT36-EESA-09A3, MOD
39688).
PN Solution
SXT30E2SA0820
SXT36EESA09A3
SXT42E2SA090A
OPS Information
QRH N°689 and FCOM3 N°275 Temporary Revisions (TR) have been
dispatched to cover this issue.
Relevant Documentation
TSM 31-63-82-810-853
Flight Operations and Training
First Issue Date: 17-JUL-2014 Last Publication Date: 21-JUL-2014 Status:
Closed
Modification on Operational Impact: YES
MODIFICATION OPERATIONAL IMPACT (M.O.I)
ASSOCIATED MODIFICATION OPERATIONAL IMPACT (M.O.I)
IS AVAILABLE.
USE ASSOCIATED LINKED ARTICLE FOR CONSULTATION.
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