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contact with the water. However, there was no visible corrosion that
may have impeded the operation of the valve. As a final check, the
BDDV was reinstalled, with its cover, in the test chamber and cooled to
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-20°C over approximately 30 minutes. It was then functioned after a
further 35 minutes, with no problems.
The BDDV was later subjected to a ‘production test’, where brake
output pressure was assessed against pedal input pressure. This
confirmed that the valve parameters met the normal production
requirements.
1.16.3. Preliminary actions taken by the Manufacturer.
Following the discovery of the water in the BDDV, and the BSCU
internal disagree condition highlighted by this event, Airbus Industrie
issued an All Operators Telex (AOT) No 32-19 dated 07 July 1998 and
an accompanying Flight Operations Telex (FOT). The AOT was
mandated by four Airworthiness Directives (AD), ref. 34, 35, 36 and
37/98 issued by Certification Authority, on 8 July 1998.
The AOT applied to all Airbus types as the same components are
used in the Alternate brake system for both the narrow and wide-body
aircraft, although in the latter, the BDDV is located close to the
centreline, ie further away from the fuselage skin.
The AOT called for a weekly check (not to exceed 9 days) of the
Alternate brake system conducted at the end of the cruise phase. This
was achieved by selecting the BSCU Antiskid & Nose Wheel Steering
switch OFF, operating the brake pedals and checking the pressure on
the triple indicator. The absence of pressure could indicate a frozen
BDDV. The failure cases were notified to Airbus Industrie and were as
follows:
A319/320/321 fleet: 40 out of 854 aircraft in service.
A310: one case out of 161 aircraft
A300/A300-600, A330 and A340: no cases.
30
The single case of BDDV failure in the A310 was considered by
Airbus to be an ‘isolated one’, with the results otherwise confirming
that the relatively exposed location of the component in the narrowbody
aircraft rendered them more vulnerable to contamination. A later
revision of the AOT reduced the check frequency to 500 flying hours.
The AOT, which required no maintenance task, was intended to be
a temporary solution pending a design fix to the BDDV. Reference was
made to a forthcoming Service Bulletin (No. A320-32-1200) which
would address this issue.
The AOT also referred to four Flight Operation Telexes (FOTs),
Nos. 999.0059; .0060; .0061; and .0062, one for each of the fleets,
setting forth an in-flight checking procedure of the Alternate braking
system and the condition of the BDDV, and the Operational
Recommendation for the event of landing brakes failure. The
Recommendation added, in connection with the Emergency Procedure
set forth for this case, the switching OFF of the BSCU A/Skid & N/W
Strg. switch after releasing the brake pedals, applying brake pressure
limited to about 1,000 psi, and as a last resort, if the brakes are still
unavailable, using the Parking Brake with short and successive
applications.
The FOT 999.0059, covered later by the Operations Engineering
Bulletin (OEB) nº 137/1 issued in September 98 applicable to the A-
319/A-320/A-321 fleet includes an additional Operational
Recommendation to avoid the “disagreement” fault in the BSCU when
selecting the appropriate Autobrake mode (LO, MED or MAX). The
Recommendation specifies that when selecting the Autobrake mode, the
push-button or switch should be firmly pressed for at least one second
in order to ensure the proper operation of the system. If, in spite of the
foregoing procedure, the fault message “BRAKES BSCU CH 1(2)
FAULT” appears in the ECAM display, without the other fault
message, ie “BRAKES AUTO BRK FAULT”, then reset the BSCU
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with the A/SKID & N/W STG switch and when the landing gear is still
retracted.
The AOT also made a declaration of intent to include in the BSCU
software Standard 8 (planned for Certification in the beginning of 1999)
the appropriate modifications in order to permanently avoid the
“disagreement” failure in the BSCU when selecting the appropriate
Autobrake mode.
1.16.4. Cold soak tests.
Airbus Industrie conducted a flight test on an A320 aircraft in
which two temperature sensors were attached to the BDDV, one on the
valve body and the other on the cover. A test flight was also conducted
on an A300-600. Once again, two sensors were used, one being attached
to the valve cover, but with the other measuring the ambient air
temperature 10 cm from the valve. Plots of the two test flights are
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