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— Operational test: The graph load vs. travel was prepared according to the Component
Maintenance Manual (CMM). It was observed that the results were outside
tolerances in a series of points both in load (compression) and extension of the cylinder.
For instance: with 10 mm of travel in load the force should be between 139
Nw and 153 Nw; the measured value was 162 Nw (7% above the specified limit).
— It was made a flow rate test under pressure. For that purpose, with the port B open,
a pressure of 2.4 bar was applied to port A and the flow vs. travel of the cylinder
was measured. In compression there was a flow of 2.17 l/min when there was no
travel and the value of the flow was being lower. With 0.33 mm the flow was 0.01
l/min and with 0.34 mm there was no flow anymore. In unload of the cylinder there
was no flow with 2 mm of travel, and the travel was reduced up to the moment
that with 0.36 mm the flow started being 0.01 l/min.
— The cylinder was disassembled and no noticeable defects were found. The different
subcomponents were dimensionally checked and all of them were found inside tolerances
except the «small» spring or spring valve (spring R1) that reached the nominal
length with a load of 4 Nw instead of the 5 Nw of the specification. The specialists
in the system considered this difference was not significant. The preformed
packing of the valve was deformed because of the contact with the valve, and had
no longer the squared section with which it was manufactured.
The cylinder was assembled again and it was adjusted in such a way that the length
and the dead travel were the same as previously, and the operational and flow rate tests
31
Technical report IN-062/2002
were carried out again. The master cylinder was now inside specified limits during compression,
but it was still slightly outside tolerances during the extension. A possible
explanation for this behaviour was that some minute particles that were producing a lot
of friction inside the cylinder could have been eliminated during the disassembly and reassembly.
After this test the length was measured again and it had increased up to
170.35 mm. The dead travel had decreased from the previous 0.58 mm to 0.48 mm,
and no clear explanation was obtained for this fact. The flow rate test provided the
same results as previously.
Messier-Bugatti informed that those cylinders are manufactured by a subcontractor. The
S/N H2121 passed its quality control after manufacture on 13-6-2000, and it was then
recorded a dead travel of 0.44 mm (inside limits) and a total travel of 21.90 mm (inside
limits), with the diagram load-travel inside tolerances. However, the length of the
cylinder was not recorded during quality control acceptance tests at that time. Messier-
Bugatti informed that «The unit is adjusted during assembly».
The acceptance test did not include a flow rate test under pressure.
Information gathered from technicians of the manufacturer indicated that they had
never seen a cylinder with a length above specifications.
The master cylinder was reserved for further investigation at the facilities of Airbus in
Filton (United Kingdom). See paragraph 1.16.5.
It was requested to Messier-Bugatti to provide an analysis of all the information
retrieved during the tests in order to establish a hypothesis of the circumstances or
the subcomponent of the master cylinder that made its length to be outside tolerances
and that ultimately produced residual pressure in the alternate system of the
A-340 EC-IDF.
Messier-Bugatti never provided a detailed analysis, but answered through an E-mail on
12-9-2003 that no subcomponent of the cylinder had been identified as defective, and
that in December 2002 they had modified their procedures to include a systematic measurement
of the length of every cylinder after manufacture. They also added that
«remains a doubt as to the possible implication of other parts such as brake pedal
assembly».
1.16.4. Inspection of the dual valve (BDDV) S/N H2718
The dual valve was disassembled from EC-IDF following a flight test carried out after
the incident. It was subject to several tests at the facilities of its manufacturer Messier-
Bugatti in Molsheim (France). The valve had been sent in a sealed package and it was
Technical report IN-062/2002
32
intended to keep inside as much hydraulic fluid as possible. However, the package was
opened at Messier-Bugatti and only 1 ml of liquid could be collected.
The recovered fluid was observed in the microscope by specialists of the manufacturer
of the component, who indicated that it contained some metal particles between 15
and 80 microns. There was not enough liquid to carry out a more complete analysis.
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