What is the purpose of auto brakes?
- Establish and maintain a consistent deceleration rate during landing, enhancing passenger comfort and reducing crew workload.
- Ensure a straight rollout while optimizing the landing distance.
- Minimize the number of brake applications, thereby reducing brake wear.
When does auto brakes activate?
- Command for ground spoilers’ extension is detected for LO and MED mode
- Command for ground spoilers’ extension is detected and aircraft speed is above 40 kt for MAX mode.
Ground spoiler function involved all spoilers and when a ground spoiler surface on one wing fails, the symmetric ground spoiler surface on the other wing is inhibited.
| Ground Spoiler Extension Logic |
| Full Extension – Rejected Take-off Phase
– Ground spoilers armed + wheel speed > 72 kt: Automatically extend when both thrust levers set to idle. – Ground spoilers not armed + wheel speed > 72 kt: Automatically extend when reverse thrust selected on one engine (other thrust lever at idle). * Speed brake not retracted is not mentioned in this case as Takeoff Config warning will warn crew against attempting takeoff with speed brakes not in retracted condition. |
| Full Extension – Landing Phase (both main landing gears on ground)
– Speed brake lever not retracted or ground spoilers armed: Both thrust levers at or below idle, or reverse selected on one engine (other thrust lever below MCT) – Speed brake lever retracted but ground spoilers not armed: Reverse selected on one engine (other thrust lever below MCT) |
When does auto brake deactivate?
- When ground spoilers are retracted, or
- When system is disarmed (flight crew presses the pushbutton switch OR after touch and go OR flight crew applies enough deflection on at least one brake pedal when autobrake is active OR when one or more arming conditions is lost).
What are arming conditions of auto-brakes?
- Green pressure available
- Anti-skid electrically-powered
- No failure in braking system
- At least one ADIRU is available
What is the difference between Autobrakes LO, MED and MAX mode?
| MAX Mode | MED and LO Modes |
| – Normally selected for takeoff. – In case of an aborted takeoff, maximum pressure is applied to the brakes as soon as the system generates the ground spoiler deployment order. |
– Typically selected for landing. – Both modes send progressive pressure to the brakes 2 seconds after ground spoilers deploy. – MED Mode: Decelerates the aircraft at 3 m/s². – LO Mode: Decelerates the aircraft at 2 m/s². |
When is maintenance action due on brakes?
Maintenance action is due in following cases:
- Temperature difference between two brakes of a gear is more than 150 deg C, and the temperature of one of these brakes is above or equal to 600 deg C, or
- Temperature difference between two brakes of a gear is more than 150 deg C, and the temperature of one of these brakes is bleow or equal to 60 deg C, or
- The difference between the average temperature of the left gear brakes and right brakes in above or equal to 200 deg C, or
- The temperature of one brake exceeds 800 deg C.
What general guidance is given in FCOM for usage of brake fans?
- When the turnaround time is short OR if the temperature of any brake is likely to exceed 500 deg C, use the brake fan without delay
- In other cases, the flight crew should delay brake fans selection to 5 min after landing, or approaching the gate, whichever occurs first
- Delaying the selection of brake fans helps limit the oxidation of any transient hot spots on the brake disk surface. Choosing to activate the brake fans before reaching gate prevents carbon brake dust from being blown onto ground personnel. The brake fans primarily blow dust during the initial seconds of operation.
Explain antiskid and Its principle?
The anti-skid system is designed to provide maximum braking efficiency by maintaining the wheels at the threshold of skidding. It optimizes brake usage by releasing brake pressure just before the wheels are about to skid on the runway. Under normal conditions, the anti-skid system is available both with and without autobrakes and automatically deactivates below 20 knots of ground speed.
The speed of each main gear wheel, measured by a tachometer, is continuously compared to the aircraft’s reference speed. The reference speed is determined by the BSCU using the horizontal acceleration data from ADIRU 1, 2, or 3. If all ADIRUs fail, the reference speed is set to the maximum of either main landing gear wheel speeds.
If a wheel’s speed falls below approximately 87% of the reference speed, the system issues brake release commands to maintain that slip ratio.
What is Autobrake LO Mode – Type 2?
Current LO mode of auto-brake (Type 1) sometimes leads to increase in utilization of manual braking to disconnect LO mode; or use of autobrake MED mode. This increases the cases for brakes oxidation. Auto brake LO Mode Type 2 provides better and more optimum deceleration. There may be reduction of landing distance up to 450m.
LO Mode Type 1 – activates 4s after touchdown and provides deceleration of 1.7 m/s2
LO Mode Type 2 – activates 2s after touchdown and provides deceleration of 2 m/s2
What is the relationship between the nosewheel steering and the rudder pedals? How many degrees can the tiller turn the nose wheel?
BSCU receives orders from hand wheel (tiller), or rudder pedals or Autopilot. BSCU transforms these orders into nose wheel steering angle.
- A lever on the towing electrical box (on nose landing gear) enables ground crew to deactivate the steering system for towing and then when can be turned 95 deg in either direction
- Tiller can turn the nosewheel up to 75 deg in either direction and this steering authority is decreases with increase in aircraft ground speed
- Orders from rudder pedals provide nose wheel steering up to 6 deg in either direction and this steering authority is decreases with increase in aircraft ground speed
Landing Gear: Airbus A320 Aircraft Systems
