Airbus A220 Landing Gear, Brakes and Steering

The Airbus A220 stands on a tricycle landing gear: a nose gear and two main gears, each with two wheels, six tyres in all. The landing gear actuation system is hydraulic and includes an alternate extension system. The four main wheels have electric brakes: 16 electric motor actuators (EMAs), driven by 8 controllers (EMACs), apply them, two brake data concentrator units (BDCUs) with normal and alternate channels are part of the control, and an autobrake is fitted. The nosewheel is steered with a tiller and the rudder pedals.

The public documents used here, the Transport Canada (TCCA) MMEL and evaluation report, the FAA Flight Standardization Board (FSB) report, the EASA type-certificate data sheet (TCDS) and the Airbus Aircraft Characteristics, cover the components, indications, dispatch rules and ground handling. They do not describe normal gear operation or the anti-skid function, and no landing gear operating speeds are given here. Dispatch conditions quoted are the MMEL's; an operator's MEL may be more restrictive. The principles are in landing gear retraction and extension, wheel brakes, anti-skid and autobrake and nose wheel steering.

Landing gear layout

The A220 has six tyres: a left and a right tyre on the nose gear, and an inboard and an outboard tyre on each main gear, each with its own tyre pressure (TPIS) fault message. The EASA TCDS and the Airbus Aircraft Characteristics give the same sizes for both models; the pressures are those of the Airbus landing gear footprint data:

The 225 mph rating is 195.5 kt; like any tyre speed limit it applies to ground speed (see brake energy and tyre speed limits). The longer A220-300 has its main gear further from the nose gear: the TCCA and FAA difference tables give a nose wheel to main wheel distance of 50 ft, against 43 ft for the A220-100. The FAA FSB report also notes larger brakes on the A220-300.

The weight-off-wheels sensing covers all three legs. The MMEL's WOW FAULT messages report a loss of redundancy in the weight-off-wheels (WOFFW) sensing of the left, right and nose landing gear; with a main gear message, at least two radio altimeters must work for dispatch. The main gear bays have overheat detection, described in A220 APU and fire protection.

Extension, retraction and alternate extension

The landing gear actuation system is hydraulic, one of the few hydraulic users the public sources name, and its MMEL item includes an alternate extension system. Dispatch with the alternate extension inoperative requires no external hydraulic leak, the nose and main gear secured in the down position and the landing gear control valve deactivated. The flight is then made gear down, under AFM Supplement 5 (flight with systems inoperative), with no steep approach and no extended or extended overwater operations. Which hydraulic system serves the gear is not stated in these sources (see A220 fuel and hydraulic systems).

The sources used here do not describe the gear lever, the normal extension and retraction sequence or how the alternate extension is worked. The MMEL lists three pushbutton annunciator lights on the main instrument panel: NOSE STEER OFF, ALTN BRAKE ON and GEAR AURAL CNCL. One brake fault message names the gear retraction, 32 BRAKE FAULT - GEAR RETRACT INOP; like 32 BRAKE FAULT - IFT INOP, it may simply be displayed for dispatch. The general logic of gear warnings is in landing gear indication and configuration warnings.

Brakes and anti-skid

The A220's brakes are electric. The MMEL's brake section lists 16 electric motor actuators (EMAs) driven by 8 electric motor actuator controllers (EMACs), for the four main wheel brakes, and no hydraulic brake components. With an EMAC inoperative, its EMAs are retracted. Each pilot's brake pedals have pedal sensors, monitored for redundancy, and two brake data concentrator units (BDCUs), each with a normal and an alternate channel, complete the control. The system has normal and alternate braking, and the ALTN BRAKE pushbutton on the main instrument panel has an ON light.

The E190-E2's brakes are commanded by wire but applied hydraulically; on the A220, as on the Boeing 787, the actuators themselves are electric (see wheel brakes and Boeing 787 landing gear and electric brakes). The 787 uses 32 actuators on eight main wheels.

The MMEL reliefs show how the parts depend on each other:

The pedal sensor rule puts the take-off and landing in the hands of the pilot whose pedal sensors are unaffected.

Anti-skid is not described in the sources used here. The MMEL does list wheel speed transducers among the brake items; in anti-skid systems generally, a transducer on each braked wheel measures its speed so that the controller can release a wheel that starts to skid (see anti-skid and autobrake).

Autobrake

The AUTOBRAKE selector, a control knob, has an OFF position. AUTOBRAKE FAIL is a caution, and dispatch with it requires the selector set OFF. The MMEL has the autobrake considered inoperative with three brake fault messages:

• BDCU 1 NORM INOP, with the other conditions in the table above;
• THROTTLE RVDT INOP, a thrust lever position sensor fault;
• WOW DISAGREE, with the added rule that braking is not applied until touchdown.

The autobrake settings and their arming logic are not given in these sources.

Brake temperature and wear

Four brake temperature sensor (BTS) readouts, one for each main wheel brake, appear on the synoptic page. With avionics Build 8.0A2 the BRAKE HI TEMP advisory was renamed BRAKE TEMP, still an advisory. 32 BRAKE FAULT - BRAKE TEMP SENSOR INOP requires operations under AFM Supplement 5 and no steep approach.

Brake wear is shown by four brake wear pins and an EICAS brake wear annunciation; with the annunciation inoperative, alternate procedures are needed.

For hot brakes, the Airbus rescue data advise fire services to apply a water mist and to approach the tyres from the front or rear, because the sides are the weakest areas of a tyre; water or dry powder is recommended for a wheel and brake fire.

Nosewheel steering

The NOSE STEER pushbutton on the main instrument panel has an OFF light. A tiller is fitted for the left seat, and a second one for the right seat is optional: with the dual installation, tiller training from the right seat is a seat-dependent task for TCCA and the FAA, and the MMEL allows dispatch with NOSE STEER FAULT - R TILLER INOP provided the left tiller works. The nosewheel can also be steered with the rudder pedals. A PEDAL DISC control on the tiller disconnects the pedal steering; if it is inoperative, the NOSE STEER pushbutton must work and the PEDAL STEER DISC status message must not be displayed.

The Airbus turning radii data run from 17° to 77° of nose wheel angle, with 3° of tyre slip, and mark 77° as the maximum. At that angle the minimum theoretical pavement width for a 180° turn is about 20.8 m (819.6 in) for the A220-100 and about 23.5 m (925 in) for the A220-300. For a 180° turn on a runway turnaround or a pivot turn, the Airbus technique is to:

1. start the turn at 5 kt or more;
2. apply full tiller when abeam the centre of the turnaround;
3. add thrust to keep 5 to 10 kt, with momentary inside braking as needed;
4. if the nose wheel slips, increase the thrust of the outside engine.

Towing and parking

For towing with the aircraft powered and the flight deck occupied, two separate controls, one to deactivate the nosewheel steering and one to deactivate the parking brake, are provided in the flight deck and on the control panel near the nose landing gear, which also has headset jacks. For an unpowered aircraft, a push-button on that panel, on the left side by the nose gear, engages power to begin the towing sequence, and the navigation lights come on automatically. The parking brake can be deactivated from the same panel, and TOW STATUS lights show NO TOW or TOW. With the torque links connected, the aircraft can be towed at nose wheel angles of up to 130 degrees either side.

Chocks depend on the wind. With the aircraft flight-ready and the wind below 25 kt, chocks go in front of and behind the inboard tyres of both main gears, without touching them. With 25 kt or more, or when the aircraft is parked or stored, the nose and main gear tyres are chocked.

How the gear connects to the rest of the aircraft, from the hydraulic supply to the weights it carries, is covered in A220 fuel and hydraulic systems and A220 family and limitations.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.