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an auxiliary low pressure circuit that actions the DUAL valve. The BSCU continues
controlling the antiskid system. The pressure sent to the left and right brakes, and
the pressure of the accumulator, appear in a triple indicator located in the centre
of the instrument panel (see Figure 1).
It is important to note that the pressure transducer to the triple indicator and to
the ECAM indication is the same. For this reason, spurious indication of residual
pressure may occur in the ECAM and in the triple indicator at the same time, and
those transducers were mentioned in the TFU (see 1.6.3) as a common cause of
the false residual pressure indication.
C) Alternate braking without antiskid: If the switch A/SKID & N/W STRG is manually
moved to the OFF position, or there is a failure in the electrical supply or failure
of the BSCU, or when there is a low hydraulic pressure in both the green and
blue systems, the antiskid system is disconnected. The control is achieved through
the pedals, that actuate the DUAL valve, while the servo valves of the alternate
system are fully open and all the pressure commanded by the pedals reach
Figure 1. View of the triple indicator of pressure. The landing gear is down, but the antiskid
switch is in OFF. Therefore, the vertical bars that represent the brakes of every wheel do not
appear in the WHEEL page of the ECAM screen
Technical report IN-062/2002
12
directly the brakes, and therefore the pilot has to regulate the pressure with the
pedals with reference to the triple indicator to avoid the lock and burst of the
wheels.
D) Parking brake: In this mode the brake receives the hydraulic pressure of the blue
system or of the accumulator through the DUAL valve. This brake may be used in
emergency.
1.6.2.4. Indications, warnings and cautions
In addition to the triple indicator mentioned above, the WHEEL page of the ECAM
(«Engine indication and alert monitoring») presents a schematic indication of the eight
wheels of the MLG that have brakes (four on the left leg and four on the right leg)
together with additional information on the brake system, including the status of the
antiskid system, of the autobrake system (AUTO BRK), rate of autobrake selected (MED),
and brake temperature (F in the attached Figure 2) of every wheel (numbered as shown
in item D in the attached figure).
Figure 2. Wheel page of the ECAM
13
Technical report IN-062/2002
On the other hand, in both sides of each wheel three vertical bars appear (item E in the
Figure 2) that represent the brakes of that side of the wheel. They appear in green
colour in flight, when the landing gear is down and the antiskid is operative, and on
ground when the brakes are released and the antiskid is active. They appear in amber
colour in the event that there is residual pressure or if there is a failure in the release
of the brakes.
The indication R («release») always appears in white colour.
There is residual pressure whenever, with the brakes released, some pressure is trapped
anywhere in the normal or alternate systems. On ground, when the pressure of at least
one wheel is above 15 bar with the pedals released, there is a «Master Caution» with
audible sound and visual indications in the page WHEEL of the ECAM. This caution is
inhibited in the ground when the speed is higher than 80 kt and during takeoff, climb,
cruise, descent and landing until the speed is below 80 kt.
The page WHEEL is automatically shown in the ECAM every time «landing gear down»
is selected, even when there is no caution or warning in the system.
1.6.2.5. Schematics of the alternate brake system
A brief and schematic description of the physical layout of the brake system of the A-
340 is presented here below, together with its situation when the alternate system is
working. For that purpose, the attached Figure 3, copied from a familiarization training
course of the manufacturer.
As it can be seen in the figure, the automatic selector allows the pressure of the alternate
or «blue» system is feeding the brake circuit. The brake distribution dual valve
(BDDV) or «dual valve» is a very important component of the system, and each of its
sides is activated by an auxiliary low pressure circuit that comes from the pedal of that
side. When the pedal is pressed, that low pressure activates the corresponding side of
the BDDV (as represented in the figure), in such a way that the blue pressure reaches the
«alternate servo valve». This servo valve opens or closes as controlled by the BSCU that
in turn receives information from the antiskid when it is active, as it happens in the condition
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