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worked correctly in a coordinated manner all the time. The local air traffic controller
(tower) that was controlling the traffic in runway 33 for landings kept the situation
under control all the time. Runway 36R was immediately inspected and was open
for traffic at 13:16 h (approximately 11 min after the aircraft came to a stop after the
incident).
2.5. Origin of the residual pressure
The tests carried out on the aircraft and at the facilities of Messier-Bugatti led to the
conclusion that the origin of the residual pressure in the left alternate brake system of
the aircraft EC-IDF was the master cylinder P/N C24592020, S/N H2121 that, once disassembled
from the aircraft, had a length of 170.31 mm (the nominal value was between
170.050 mm and 170.100 mm) and a dead travel of 0.58 mm (the nominal value
was between 0.40 mm and 0.50 mm).
With those dimensions, the cylinder had to be compressed at the moment of assembly
on the aircraft, in a way that made the dead travel to be 0.37 mm, which is 0.03 mm
below the lowest tolerance of the specified value.
45
Technical report IN-062/2002
In those conditions, the alternate system could work in a normal way during a lot of
flights or during a lot of phases of those flights, with the only difference that the aircraft
would start braking with an angle of pedal deflexion slightly below the nominal
value. However, due to the thermal expansion of the hydraulic fluid during the descent
from cruise, under certain conditions, it is probable that the dead travel was plugged,
thus preventing the return of hydraulic fluid from chamber C1 to chamber C2 of the
cylinder, and eventually building up the residual pressure.
The master cylinder had passed its quality control after manufacture on 13-6-2000, and
the dead travel was then measured to be 0.44 mm and the total travel 21.90 mm, with
the load-travel diagram inside tolerances. The total length of the cylinder was not required
to be recorded during the acceptance tests at that time. Therefore, it could not be
documented whether the cylinder was already outside specifications after manufacture
or whether the length of the part was unsettled later on, although it seems more probable
the first possibility.
The defective internal subcomponent of the cylinder that was producing the difference
in actual length with respect to the nominal length, or the part of the cylinder that was
ultimately responsible for the build-up of residual pressure could not be determined. No
detailed analysis of the behaviour of the component was received from Messier-Bugatti.
On the other hand, although Airbus carries out flight test after manufacture of their aircraft
with duration of about three and a half hours, from which there are two hours at
cruise altitude, and also the operator carries out acceptance flight tests, those flights did
not detect any residual pressure. Since the flights did not include long periods of cruise
at high altitude, it is probable that they did not produce thermal changes important
enough during descent. However, the flight Tenerife-Madrid had a profile somewhat
comparable to that of the flight tests (regarding time at cruise altitude) and there was
indeed residual pressure.
2.6. Previous history of residual pressure
The aircraft was delivered by the manufacturer to the operator in May 2002. Until the
date of the incident it had completed 131 flight cycles.
Since 7 to 11 of June 2002 there were five abnormalities reported regarding presence
of residual pressure in flight in the wheels of the left leg. In the two first cases, there
was an important increase of temperature of the brakes during the landing roll.
One of the squawks indicated «In descent with clean configuration the brakes residual
braking lights on brake 1, 2, 5 and 6, at parking 500 °C + of temperature reached».
Another report said: «In approach residual pressure in left leg brakes. Solved after seve-
Technical report IN-062/2002
46
ral resets of nose wheel steering switch (there was indication of pressure in the brake
indicator) and pressing the brakes at the same time. See previous reports».
Additionally, in year 2001 there was a long history of residual pressure that affected A-
340 EC-GUP of Iberia. The problem was reported to Airbus that worked with the operator
to solve the problem. The TFU 32.42.21.002 stated that «Operator’s reports have
shown that the ´Brakes residual braking ECAM warnings are often spurious», although
it was also mentioned that they could be real and troubleshooting was needed to confirm
the fault. Airbus stated that they were never formally informed of the results of the
recommended trouble shooting actions of EC-GUP.
　
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