Flight recorder data
Data reviewed following the flight confirmed that approximately
3 minutes after full power application for takeoff, the fuel flow
to the right engine dropped to zero, resulting in the subsequent
in-flight shutdown of the engine.
Component history
Documentation provided by the operator annotated that the EEC
part number 114E6112G119, serial number LHBR0141, had accumulated
426.7 hours time since new, 393 cycles since new, and had been
installed on 2 August 2002. The unit had been modified to software
version 6.1 (the most recent version).
Electronic engine controller
The EEC was a two-channel (A and B) electronic unit with system
redundancy. It controlled, among other items, engine start
sequencing, power requirements, operating temperature, turbine
speeds, fuel flow, engine monitoring, and automatic relight. It
contained fault detection, storage, and readout capabilities, all
stored on an electrically erasable/programmable read-only memory
(EEPROM) located on a computer board assembly. The EEPROM provided
a history for troubleshooting purposes of any fault event within
the EEC or associated control systems by logging a fault code of
the event. Those fault codes were then stored until intentionally
cleared during maintenance action. The distinct two channels in the
unit ensured that should one channel fail, the other would assume
control and monitoring of the engine. The transfer of control and
monitoring of the engine to one EEC would not necessarily signify
that other items controlled by the non-controlling channel would
not function. The EEC also provided an electrical signal for
opening the engine fuel-control metering valve (normally closed)
upon engine starting, which was spring loaded to the closed
position.
Component testing
The EEC and FMU units were shipped to the respective component
manufacturer's facilities for testing under the supervision of the
United States of America (USA) National Transportation Safety
Board. Representatives from the aircraft, EEC and engine
manufacturers were also present for the testing. Testing of the FMU
revealed no anomalies.
EEC serial number LHBR0141 testing
During environmental stress screening of the EEC (a high-speed
scan of the faults over a temperature cycle alternating from -55 to
+74 degrees C), failures of the Channel A EEPROM were recorded when
the internal temperature of the EEC was at -2 degrees C or colder.
Test procedures used to test new units for acceptance, also
revealed faults of the Channel A EEPROM at temperatures below -55
degrees C. However, initial testing of the EEC could not duplicate
the dual channel failure (A and B) that would have been required to
sustain the reported in-flight shutdown.
The Channel A EEPROM was sent to the manufacturer for detailed
examination. Examination indicated that a phenomenon called a
'single bit flip' had occurred within the used memory section area
of the input/output microprocessor of the unit. The input/output
microprocessor memory was configured with positively charged
hexadecimal binary 1s occupying unused memory sections. The 'single
bit flip' phenomena was a result of unused sections of the
microprocessor memory becoming negatively charged binary zeros,
resulting in checksum failures and 'health lane' degradation of the
EEC. Checksum failures are the result of discrepancies of the
internal self-check program, which sums the values of all memory
blocks.
Follow up vibratory testing of the EEC confirmed a failure of
Channel B. Further examination indicated fracturing of solder
joints at five resistors on the analog interface module circuit
board of Channel B.
Other Australian fleet occurrences
On 24 November 2002, while on the downwind leg for landing at
Hobart, another crew of the same aircraft reported that the left
engine 'spooled down'. The crew reported that they did not see any
caution advisories prior to the power decrease. The crew then
completed a single engine landing. Following the event, the
operator's maintenance personnel conducted troubleshooting of the
left engine and noted one fault code related to the EEC (not listed
in maintenance documentation) logged on the MCDU memory. The engine
was inspected and ground run, both at idle and at a high power
setting. The engine started and operated normally. The EEC and FMU
were replaced after conferring with the engine manufacturer.
Further engine ground runs were completed and the aircraft was
deemed to be serviceable.
Documentation provided by the operator recorded that the EEC
part number 114E6112G119, serial number LHBR0148, had accumulated
4,686.4 hours and 4,311 cycles since new. The unit had been
modified to software version 6.1.
The engine manufacturer advised that a visual inspection of the
unit revealed fracturing of the soldier joints of six resistors of
Channel A and four resistors of the Channel B analog interface
module circuit boards.
Other overseas occurrence
On 30 November 2002, a USA operator's Boeing 717-200 was on
climb at FL 280 when it sustained an in-flight shutdown of the
right engine. Following the event, EEC part number 114E6112G119,
serial number LHBR0093, which had accumulated approximately 6,700
hours time since new was examined. That examination revealed
fracturing of the solder joints at five resistors of Channel A and
ten resistors of the Channel B analog interface module circuit
board.
Solder joint fracturing
The engine manufacturer reported that the anomaly of fracturing
or cracking of the resistor solder joints was believed to have
resulted from thermal cycle induced stress due to differential
thermal expansion between the printed circuit board and the
resistor. They further reported that identical resistor packages
were utilised on the installation of both channels within the EEC
and that the solder joint fracturing anomaly could affect a total
of seven resistors per channel of each EEC. Five of these resistors
were assessed as being capable of contributing to the top-level
failure events analysed in the unit system safety assessment.
Service bulletin history
On 20 December 2002, the engine manufacturer issued Service
Bulletin SB-BR700-73-101401. That bulletin referenced compliance
with the EEC manufacturer's Service Bulletin SB-BR715/73-009 also
released 20 December 2002, which gave instructions for the repair
of several specific resistors on the analog interface module
circuit board. That repair would attach the resistors to the board
and connect them to the original solder pad by 'flying leads'. This
would then eliminate any mechanical stress on the resistors.
Compliance time of that bulletin was at the next shop visit of the
EEC for repair, or as arranged by the EEC manufacturer and was not
mandatory.
On 17 January 2003, the engine manufacturer issued Service
Bulletin SB-BR700-73-101404. That bulletin referenced compliance
with the EEC manufacturer's Service Bulletin SB-BR715/73-010 also
released on 17 January 2003, which gave instructions for a software
modification of the processor communication's modules (A3, A4) with
new input/output software to change the fill pattern of the unused
areas of the EEPROM memory from hexadecimal binary 1s to binary 0s,
thereby reducing the possibility of checksum failures. Compliance
time of that bulletin was at the next shop visit of the EEC for
repair, or as arranged by the EEC manufacturer.
On 20 February 2003, the engine manufacturer issued Service
Bulletin SB-BR700-73-900316 advising the fleet operators of a
numbers of inspections and modifications to improve the reliability
rates of the EEC. The bulletin listed a total of ten service
bulletins issued by either the engine or EEC manufacturer, which
the engine manufacturer recommended be incorporated at the earliest
opportunity without affecting flight schedule. Incorporation of
these modifications required a return of the component to the
engine manufacturer.
None of those service bulletins were mandated through the
issuing of an airworthiness directive from either the USA Federal
Aviation Administration or the German Airworthiness Authority.