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which the landing gear was lowered, at 12:58:38 h when the aircraft was approximately
at 4000 ft. At that moment, the page WHEEL of the ECAM was automatically
deployed and the aircraft carried out several auto checks of the hydraulic system, and
the normal brake system was momentarily connected and the residual pressure of the
left side released until the checks finished and returned to its previous value.
They carried out another reset «cycle» of the BSCU, for 24 s. This action, carried out
once the landing gear was down, was contrary to the operational procedures of the aircraft,
and was unable to make disappear the amber bars, although they probably disappeared
momentarily while the BSCU switched off and then on.
Should the crew checked and interpreted correctly the triple indicator, they would have
noticed that the residual pressure was in the alternate brake system, which is not controlled
by the BSCU. This could have help conclude that the resets of the BSCU would
not be effective in the build up of residual pressure.
Under those conditions, there was a conversation in the cockpit in which it was said that
one possibility would be to disconnect the antiskid, with the intention, according to the
later statements of the crew, of avoiding that electronic systems not controlled by the pilots
applied or released braking pressure in the uncertain conditions in which the whole system
seemed to be. Finally they disconnected again the switch A/SKID & N/W STRG that was
maintained in that condition for the remainder of the approach and landing. Thus, the possibility
of activating the normal brake system (that had no residual pressure and that would
have been activated at the moment of pressing the brake pedals) was precluded.
The autobrake system was not armed, and anyway it would not have functioned because
the antiskid was disconnected.
The aircraft continued its approach and the crew commented the possible behaviour of
the system during the landing. The conversations indicated that there were certain
Technical report IN-062/2002
42
doubts about the functioning of the brakes in the status they were. The copilot read
the corresponding part of the Operations Manual, reminding clearly that the pressure
should be checked in the brake indicator and that it should not be above 1000 psi any
time, because otherwise the wheels would burst.
Almost simultaneously to the moment the tower authorized the landing in runway 33,
with wind 210° and 10 kt, the crew decided to land close to the threshold of the runway
and use reverse without touching the brakes. At those moments, the «Glide slope
» warning of the GPWS sounded, with the aircraft at 600 ft of radio-altitude. The
PF said that this warning should be disregarded because, according to a later statement,
he wanted to carry out a somewhat low approach to touchdown as soon as
possible.
On the other hand, with the time employed in the revision of the brake system in the
manuals and deciding what to do regarding the residual pressure, it is very probable
that the checklist of final was not read and completed (paragraph 2.01.63 of the Operations
Manual of the operator). One of the consequences of this fact was that the spoilers
were not armed during landing.
There were no special instructions given to the passengers and the tower was not advised
that some abnormality with the brake system could appear, to allow the fire fighters
to take positions with time in advance. As it happened in Tenerife-Norte, at least a
high brake temperature could be expected that even produced smoke at that airport.
Those facts must be regarded as being a part of a situation with high workload and
some uncertainty inside the cockpit. The workload would have been produced by the
mental evaluation of the different malfunction scenarios of the brakes and the corresponding
corrective actions, and the use of the manual, which eventually absorbed most
of the attention of the crew at those final moments of the approach. Even though there
was available time during the cruise flight, the crew was exposed to face the problem,
look up for information and make decisions in the moments previous to the landing,
after having lowered the landing gear.
The aircraft floated for 3 s in the flare until the right and left MLG legs touched down
about 240 m after the threshold of runway 33, at 13:03:27 h. Since the antiskid was
inactive, there was no momentarily release of pressure as it happened during touchdown
in Tenerife. Therefore, when they contacted the runway, the left wheels where
locked and it is probable that they burst soon afterwards.
Approximately 7 s later, the copilot asked whether the aircraft had a tendency to deviate.
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