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Technical report IN-062/2002
Registration: EC-IDF
Year of manufacture: 2002
M.T.O.W.: 275000 kg
Operator: Iberia L.A.E.
Total flight time: 960 FH
Total flight cycles: 133 FC
1.6.2. Description of the brake system of the A-340-313
According to the description of the Operations Manual prepared by the operator of the
aircraft, the A-340 has brakes in the wheels of the right and left MLG (the central leg
of the MLG does not have brakes) that may be applied by any of the two independent
brake systems (normal system, or green system, and alternate system, or blue system).
There are also autobrake and antiskid.
The brake commands may come from the pilot, when the brake pedals are pressed, or
from the autobrake, with a deceleration rate previously selected by the crew. When in
normal mode, all those commands are controlled by the Brake System Control Unit
(BSCU) that has two channels. The alternate (blue) system is hydromechanical.
This BSCU also checks the residual pressure and the temperature of the brakes and provides
information on the speed of the wheels to other systems of the aircraft.
In flight, only the alternate system is pressurized and available. During landing, the brakes
revert to the normal system at the moment the brake pedals are pressed or at the
moment of touchdown if the autobrake system is armed.
When the normal system pressurizes and is active, the feed of pressure to the alternate
system is automatically cancelled. The brakes also momentarily revert to the normal
system in flight when the landing gear is lowered, while several auto tests are being
performed in the brake system.
1.6.2.1. Antiskid system
The antiskid system provides a maximum braking efficiency maintaining the speed of
the wheels at the limit of slipping. The antiskid function is automatically disconnected
on ground when the speed is below 10 kt. There is a switch (A/SKID & N/W
STRG) in the cockpit with to positions (ON/OFF) that allows the manual connection
and disconnection of the antiskid and the nose wheel steering functions at the
same time.
Technical report IN-062/2002
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The antiskid system never increases the pressure by itself, but simply releases or maintains
the pressure applied by other parts of the system (the pedals or the autobrake).
1.6.2.2. Autobrake system
This system reduces the delay in the braking action in the event of an acceleration-stop
to improve the performances and establishes and maintains a deceleration rate during
landing to improve the comfort and reduce the workload of the flight crew.
The system may be armed before the landing pushing the switches LO, MED or MAX
(braking rate low, medium or maximum) under certain conditions, including that the
antiskid system must be electrically energized.
During the landing roll the autobrake action starts with the command to extend the
spoilers.
The normal procedures of the operator (Operations Manual A340, 2.01.63, 4-12-2000)
indicate that in final the autobrake may be selected at LO or ME («if required») and
then add: «In the event of crosswind, contaminated or short runway, or under low visibility
conditions, select LO or MED. In a dry runway of normal length, normally the use
of autobrake is not necessary».
However, the procedures recommended by the manufacturer of the aircraft indicate:
«Use of the autobrake is recommended.
Use of MAX mode is not recommended at landing.
On short or contaminated runways, use MED mode.
On long and dry runways, LO mode is recommended.
Note: If, on very long runways, the pilot anticipates that braking will not be needed,
use of the autobrake is unnecessary.
Press the appropriate pushbutton, according to runway length and condition, and
check that the related ON light comes on.«
1.6.2.3. Brake modes
There are four modes of operation of the brakes:
A) Normal braking: when there is hydraulic pressure of the first system, called green
hydraulic pressure and the switch A/SKID & N/W STRG is in ON, among other conditions.
The control is electrical through the BSCU, and the braking command is
provided with the pedals or automatically by the autobrake (on ground) or when
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Technical report IN-062/2002
the landing gear lever is moved to «UP» (in flight). There is no indication to the
crew of the hydraulic pressure applied to the brakes.
B) Alternate braking with antiskid: when the normal or green hydraulic pressure is not
enough, and the switch A/SKID & N/W STRG is in the ON position, there is an automatic
selection of the blue or second hydraulic system, and the alternate braking
system is available. In this case, the control is achieved through the pedals through
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