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appended (Appendix E, Figures 3 and 4).
It can be seen that on the A320 test, the temperature before takeoff
was 30° C. After take-off, the temperature reduced at approximately
0.6° C per minute, with 0° being reached after 50 minutes. The lowest
temperature was –8° C, when the total air temperature (TAT) was –22°
C. During the cooling process the sensor on the valve cover
consistently registered 2° C below that of the one on the valve body,
possibly because of the higher thermal inertia of the latter. The TAT
then rose to –10° C and the valve cover temperature stabilised at –6 °C.
For the flight profile flown, the valve temperature rose above –0 °C, 10
minutes after leaving flight level 330 with –10 ºC of TAT. After
landing, the Antiskid system was switched off and Alternate brake
pressure was confirmed.
In the A300 test the TAT reduced rapidly to a low of –30° C, with
the BDDV valve cover temperature reducing at around 0.9° C per
32
minute to a minimum value of –14° C. The aircraft then flew at lower
altitudes than for the A320 test, so that the valve temperature was above
zero for one and a half hours before landing.
1.16.5. Analysis of the fluid found inside BDDV cover
The DERA Fuels and Lubricants laboratories separated the water
based contaminant fluid found within the BDDV into three phases;
water, oil and a solid sludge:
a) The water contained a significant concentration of detergent
(>0.25%), indicating contamination by a cleaning fluid or solution. .
b) The oil was essentially phosphate ester hydraulic fluid with
small amounts of trichloroethylene and high molecular mass
hydrocarbons.
c) The sludge contained a number of elements, the most
predominant being silicon, indicating the presence of a silicone based
grease.
Analysis of the hydraulic fluid samples taken from the BDDV
valve ports showed consistency with normal phosphate ester type
hydraulic fluid, with traces of pentane and 3-methyl pentane, possibly
from solvent cleaning. All the samples were clear and bright, but
contained either suspended particles or fine sediment.
The owner and operator provided details of the proprietary
cleaning fluids used in aircraft washes. Samples of these were mixed
with water at the dilutions required by the manufacturers and tested by
DERA in order to determine the freezing points. It was found that these
varied between 0 °C and –0.75 °C. It is understood that the usual
concentration for cleaning was one part detergent to 20 parts water.
33
1.16.6. BDDV history.
The BDDV was manufactured in August 1992 as Part Number
A25434004-3A, with Serial Number 1255. It was fitted as original
equipment to a Monarch Airlines A320, G-OZBA in March 1994. It
was removed on 28 November 1996 and returned to Messier-Bugatti as
part of a rolling modification programme on the component. This
involved the embodiment of three Service Bulletins (SBs), Nos 580-32-
3091, -3099 and -3103. These respectively changed the valves’
input/output characteristics, checked a chamfer on one of the internal
valve lands (which eliminated a potential problem with uncommanded
application of brake pressure) and deleted the automatic bleeding
facility. In fact SB 580-32-3099 was found already to have been
embodied. The unit was released back to Monarch under a new Part
Number, A25434006–2A, although the original serial number was
retained. The accompanying release paperwork included a JAA Form 1,
which was dated 24 December 1996.
Leisure International obtained the BDDV from Monarch and
installed it on G-UKLL on 5 February 1997, the unit it replaced being
returned to Messier-Bugatti for the same modifications to be embodied.
The BDDV remained on the aircraft until the accident. There was no
record of any further maintenance being carried out on the unit.
1.16.7. BSCU history and tests.
The BSCU, Part No C20216332292C Amendment A, Serial No
329, was fitted to the aircraft in February 1997 and had achieved 4,719
hours at the time of the accident. The unit was received from Messier-
Bugatti with software Standard 7 installed.
The BSCU was tested on an automatic test facility at Aerospatiale,
Toulouse. A failure was detected and subsequently the unit was
disassembled to its individual circuit boards.
34
During this process it was observed that some of the components
close to the ventilation holes in the casing were covered with what
appeared to be carbon deposits. It was considered that this could have
originated from the exhaust gases of ground power units parked close to
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