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the avionics bay air inlet. This did not appear to have affected the
functionality of the boards however.
The only confirmed defect was a failed relay which controlled the
LO Autobrake ON and DECEL lights on the switch panel. This
accorded with the report of the ferry flight made from Ibiza to Toulouse
on 17 June, following its temporary repair.
No other failures were detected and the non-volatile memory
contained the failure messages relating to the accident flight and the
subsequent testing.
1.16.8. Brake Control Panel Tests.
The Brake control panel, located in the cockpit, was tested on the
appropriate test rig at Aerospatiale’s Toulouse facility. It was found
that one of the two bulbs in the MED Autobrake ON push switch had
blown. Otherwise the unit functioned satisfactorily.
The contacts of each of the Autobrake switches are maintained at
14 volts; pressing the switch grounds the contact, thus giving zero volts.
This is detected by the two “command” and “monitor” functions within
the BSCU, which enter the appropriate MAX, MED or LO Autobrake
selection.
The switch panel was subsequently tested on Airbus Industrie’s
engineering test rig (the “iron bird”), with the switch function being
visualised on an oscilloscope. This showed that when the switch was
pressed, the voltage drop was virtually instantaneous after some “noise”
35
lasting approximately 2 milliseconds. Thus the period at zero volts was
effectively the same duration as the button-push less 2 milliseconds.
The use of the oscilloscope allowed a further opportunity to
provoke the COM/MON channels disagree within the test rig’s BSCU,
as each channel’s Autobrake ON/OFF state was represented by a
different voltage line. Usually, and according to the expected
functioning, both channels would change simultaneously on pressing
the Autobrake LO switch; however, if the push was less than
approximately 50 milliseconds and more than 20 milliseconds (which
was quite difficult to achieve in practice), only one of the COM/MON
functions would change state, and the other would not. The oscilloscope
charts with the voltages for the COM/MON functions plotted to
Auto/brk LO button push are shown in Appendix F.
1.16.9. Relevant aircraft history.
The operator supplied a record of braking system defects for the
period 1 January to 20 May 1998. These were few in number and were
mainly concerned with brake pads being worn to limits, or high brake
temperatures being noted after landing. There were no recorded
problems with brake functioning or operation.
A Major Check “C” was carried out on the aircraft 14.5 flying
hours before the accident. According to the Operator, the only item
remotely relevant to the accident was the replacement of the No 2 brake
assembly.
In view of the fact that detergent was found within the BDDV, the
recent history of aircraft washes, which was carried out by a contractor,
was obtained. This was as follows:
19 May 1997 Belly wash by hand
26 May 1997 Belly wash by hand
9 June 1997 Full Wash
36
16 June 1997 Belly Wash
14 July 1997 Belly Wash
28 July 1997 Full Belly Wash
6 August 1997 Spot Wash
13 November 1997 Full Wash
The contractor ceased the washing services after November 1997,
following which the washing history is incomplete. However, the
contractor´s procedures provided for hand washing of the landing gear
indicated that the washes were conducted with the wheel well doors
closed, thereby shielding the hydraulic system components, including
the BDDV, from direct impingement from hose pipes.
1.17. Organisational and management information.
Not applicable.
1.18. Additional information.
1.18.1. Subsequent Actions by the Manufacturer on the BDDV
On 5 September 1998, Airbus Industrie issued Service Bulletin
No. A320-32-1200, which advised all operators of A319, A320 and
A321 aircraft of the issue of Messier-Bugatti Service Bulletin No.
A25434-32-3172. This proposed the modification of the BDDV by
drilling a 6 mm diameter drain hole in the bottom side of the cover and
lubricating all parts of the rocker arm mechanism inside the cover. This
was intended to prevent the accumulation of large quantities of water
inside the cover, and to prevent jamming of the rocker arm mechanism
under freezing conditions. The information page on the Bulletin
concludes as follows:
37
Accomplishment of this Service Bulletin is recommended in
the event of failure of the weekly in-flight check of the functioning
of the Alternate braking system, required by Airworthiness
　
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