Landing Gear (A320)

These notes cover the landing gear, nose wheel steering and brakes of the Airbus A320, written as questions and answers. If anything here conflicts with your FCOM, the FCOM wins.

Gear operation and emergency extension

When the aircraft flies faster than 260 knots, a safety valve cuts off the green hydraulic supply to the landing gear. If ADR 1 and 3 both fail, the safety valve is commanded closed, retraction does not work and the gear must be extended by gravity.

When a crew member turns the emergency extension crank handle, it isolates the gear hydraulics from the green system, unlocks the gear doors and the main and nose gear, and lets gravity drop the gear down. After that, nose wheel steering is not available, and the gear doors stay open.

Two landing gear control and interface units (LGCIUs) control gear extension, retraction and door operation. They send gear data to the ECAM and tell other systems whether the aircraft is in flight or on the ground. One LGCIU controls a complete gear cycle and then hands over to the other after retraction, or at once if it fails. There is no visual way to check the gear position. A mechanical main gear uplock holds the retracted gear. It closes mechanically and opens hydraulically in normal operation.

Indications and warnings

• Red UNLK lights show that a gear is not locked in the selected position. The lights on the gear indicator panel stay on as long as LGCIU 1 has electrical power.
• The red arrow on the gear lever lights if the gear is not locked down in landing configuration, with a red ECAM warning.
• In that case the crew also get the aural crc, the master warning light, the down arrow light on the gear panel and the GPWS TOO LOW GEAR call.
• LDG CTL in amber on the ECAM WHEEL page means the lever and the gear position disagree. It appears only while the gear is moving.
• GEAR NOT DOWNLOCKED means one gear is not downlocked with the lever down.
• GEAR NOT DOWN appears if the gear is not downlocked and radio height is below 750 feet with both engines under 75 percent N1 (or the remaining engine under 97 percent if one is shut down), or with both engines not at takeoff power and flaps at 1, 2, 3 or FULL, or with flaps at 3 or FULL and both radio altimeters failed.
• On the WHEEL page each gear has two triangles. The left one belongs to LGCIU 1, the right to LGCIU 2. An amber cross in place of a triangle means that LGCIU has failed. A red triangle means an LGCIU sees a gear in transit.

Nose wheel steering

Nose wheel steering is not available if the yellow hydraulic system is inoperative. Using the rudder pedals, the steering angle starts to reduce at 40 knots and falls to zero at 130 knots, and above 130 knots the pedals do not steer. The hand wheels can steer through plus or minus 75 degrees up to 20 knots, and the angle then reduces steadily to zero at 80 knots.

With the towing control lever in the tow position, the ECAM shows NW STRG DISC in green. After the first engine starts, the message turns amber.

Brakes

The aircraft has two brake systems. The normal system uses green hydraulic pressure. The alternate system uses the yellow system, backed up by the hydraulic accumulator. In normal operation a dual channel brake and steering control unit (BSCU) controls normal braking and antiskid. Autobrake works on the green system and is lost when braking drops to alternate with antiskid. The alternate system is not as capable as the normal one.

Braking drops to alternate without antiskid if the antiskid and nose wheel steering switch is off, power fails, or the BSCU fails, or if yellow and green pressure are both low, leaving only the accumulator. The accumulator is built to supply at least seven full brake applications.

The antiskid turns itself off below 20 knots of groundspeed.

Autobrake

After touchdown with autobrake selected, the ground spoilers must move before auto braking begins. In a rejected takeoff, autobrake needs a speed of at least 72 knots to activate. The modes are:

• LO sends progressive pressure 4 seconds after the ground spoilers deploy, to slow the aircraft at 1.7 m/s squared (5.6 ft/s squared).
• MED sends progressive pressure 2 seconds after spoiler deployment, for 3 m/s squared (9.8 ft/s squared).
• MAX is normally selected for takeoff. In an aborted takeoff, maximum pressure goes to the brakes as soon as the ground spoiler order is given.
• The blue ON light shows positive arming, and the green DECEL light comes on when actual deceleration reaches 80 percent of the selected rate.

Green AUTO BRK on the WHEEL page means autobrake is armed, and a flashing green memo shows for 10 seconds after it disengages. On slippery runways, antiskid may stop the aircraft reaching the set deceleration so the DECEL light stays off, but autobrake still works.

Parking brake, temperatures and speeds

Setting the PARK BRK switch ON deactivates the other brake modes and supplies the brakes with yellow high pressure. The ECAM memo shows PARK BRK. The accumulator holds parking pressure for at least 12 hours. The BRAKES and ACCU PRESS indicator shows the pressure in the yellow brake accumulator, and the yellow pressure delivered to the left and right brakes, measured after the alternate servovalves.

• Maximum brake temperature for takeoff with the brake fan is 150 degrees Celsius.
• If brake temperatures are above 300 degrees at the gate and brake fans are on, switch the fans off at about 250 degrees.
• Maximum gear retraction speed (VLO) is 220 knots.
• Maximum gear extended speed (VLE) is 280 knots or Mach 0.67.
• Maximum gear extension speed (VLO) is 250 knots.
• Maximum gear extension altitude is 25,000 feet.

Part of the A320 systems series. See also Airbus Tech. Your FCOM is always the final reference.