Nose Landing Gear

The nose landing gear (NLG) carries only about 8% of the aircraft weight, but it does two things the main gear does not: it provides ground directional control (steering), and it must realign its own wheels straight after lift-off — otherwise a skewed wheel would be retracted into the bay and extended skewed next time. Per FCOM DSC-32-10-10:

The two-wheel nose gear comprises an oleopneumatic shock strut and a nosewheel steering system. It retracts forward into the fuselage.

And per AMM 32-21-00:

The nose landing gear (NLG), with a twin-wheel axle, is installed in the forward fuselage and retracts forward into the NLG bay... A dragstay assembly keeps the NLG rigid and downlocked when it is extended.

This article is best read against the Main Landing Gear, because almost every NLG design choice is the opposite of the MLG's. Nosewheel steering control itself is developed in Nosewheel Steering; this article covers only where the steering mechanism attaches.

1. Nose gear vs main gear — the differences at a glance

The fastest way to learn the NLG is by contrast with the MLG you already know:

The one-line model: the MLG is a load-bearing four-wheel carrier that changes shape; the NLG is a steering, self-centring, two-stage strut.

2. Mounting — twin trunnions on the keel beams

The NLG main fitting is a barrel with two cross members and two side members, forming two triangles (the MLG main fitting forms only one; the NLG needs left-right symmetry to react steering and ground side loads). The outer lugs each hold a trunnion pin. Per AMM 32-21-00:

A pair of trunnion pins attach it to the aircraft structure, through bearings in the keel beams... transmit vertical and horizontal loads to the aircraft structure.

Note the contrast in attachment: the MLG hangs off the wing rear spar (pintle + side stay); the NLG hangs off the forward-fuselage keel beams (a pair of trunnions). The main fitting also carries a machined, chromed surface on which the NWS rotating sleeve turns — the interface between the steering mechanism and the structure.

3. The two-stage oleo — why split into two stages

This is the most distinctive NLG mechanism. The MLG is single-stage (one gas chamber); the NLG is two-stage — a sealed floating piston inside the tube divides the gas into two chambers. Per AMM 32-21-00:

Inside the tube is a sealed floating piston. The space below the floating piston makes the second stage gas chamber and the space above makes the recoil chamber.

With the first-stage chamber charged through the inflation valve at the top of the inner tube, the absorber has two gas springs. On compression they work together. Per AMM 32-21-00:

The decreasing volumes in the first and second stage gas chambers increases the gas pressure which absorbs the compression load.

Why two stages. The two chambers are charged to different initial pressures (first stage 12 bar, second stage 55 bar — see the Overview hard numbers). Light loads (taxi bumps) are absorbed mainly by the soft first stage, giving a smooth ride; heavy loads (a hard landing) compress into the stiff second stage. One strut therefore delivers a progressive stiffness — soft for small impacts, stiff for large ones — which a single-stage absorber cannot do.

Damping is tapered. Per AMM 32-21-00:

The metering tube has tapered channels along its length that increases its damping effect through the diaphragm as the shock absorber compresses.

The deeper it compresses, the harder the taper makes the fluid flow, the greater the damping — automatically heavier cushioning as it nears the bottom, preventing a hard touch-down to the stop. Compression is metered through the diaphragm orifice and an opening plate valve; extension closes the plate valve and meters flow through restrictor/diaphragm orifices to slow it. As on the MLG, the recoil (extension) stroke is deliberately slow.

4. The centering cam — self-aligning off the ground

A mechanism the NLG has and the MLG does not. Per AMM 32-21-00:

An upper and a lower cam between the sliding tube and the inner tube makes sure that the nose wheels are correctly aligned (when the NLG is off the ground). They also make a travel stop during operation of the shock absorber.

As the absorber extends after lift-off, the matching ramps of the upper and lower cams slide against each other like two wedges and mechanically rotate the sliding tube — and the wheels with it — back to centre. So even if the nosewheel is skewed at the moment of rotation, it self-centres the instant the gear is off the ground, ensuring a straight wheel is retracted and extended straight next time. This pairs with the operation-level fact that the BSCU inhibits steering output once the shock absorber is fully extended: off the ground, steering is inhibited and the cams centre the wheel — two safeguards together.

5. Torque links that also carry steering

The MLG torque links only stop the sliding tube rotating. The NLG torque links do that and transmit steering. Per AMM 32-21-00:

A pair of torque links, installed from a rotating tube on the main fitting to the integral lugs on the sliding tube, transmits steering inputs from the NWS to the nose wheels.

The path is: the NWS steering actuators turn the rotating sleeve on the main fitting → the torque links → twist the sliding tube → the nose wheels turn. The torque links are therefore both the alignment member (stopping free rotation) and the steering drive — one part, two jobs.

6. Dragstay and lock stay — the overcentre downlock, two springs

Extended, the NLG is held rigid and locked by the dragstay assembly — the same principle as the MLG side stay (an overcentre geometric lock), but with half the parts. The dragstay's two links share a centre pivot pin, and that centre pivot doubles as the uplock roller. Per AMM 32-21-00:

The center pivot is also the uplock roller.

The lock stay sits between the main fitting and the dragstay centre pivot, with a mechanical overcentre stop between its links to prop the dragstay when extended. Two downlock springs (the MLG has four) hold the lock stay overcentre; on a gravity extension, spring tension pulls the lock stay to the mechanical overcentre lock. Per AMM 32-21-00:

If a downlock spring is fractured, the one that is serviceable is sufficient to complete this function.

Note the redundancy margin: the MLG is 4, three enough; the NLG is 2, one enough — tighter, but still single-fault-tolerant for a reliable locked extension.

[!warning]- Five misconceptions this article corrects (1) The NLG shock absorber is not single-stage like the MLG — it is two-stage (a floating piston splits the gas into two chambers) for a progressive soft-then-stiff response. (2) A skewed nosewheel at rotation does not stay skewed — the centering cam realigns it off the ground. (3) The NLG torque links do not only prevent rotation — they also transmit steering (NWS → rotating sleeve → torque links → wheels). (4) The NLG does not extend on hydraulics alone — airflow (forward retraction) and its own weight help. (5) A single broken downlock spring does not prevent extension — one of the two is enough, though the margin is tighter than the MLG's.

7. The dual-seal gland — same idea as the MLG, opposite default

The NLG absorber gland is also a backed-up, two-seal design, but the seal in use by default is the opposite of the MLG's. Per AMM 32-21-00:

Usually the bottom set of seals keeps the pressure in the shock absorber... If there is a leakage of hydraulic fluid from the upper guide area, the seal changeover valve can be closed. This causes the pressure differential to transfer to the top set of seals.

For contrast: the MLG uses the top seal by default and switches to the lower seal (changeover valve opened); the NLG uses the bottom seal by default and switches to the top set (changeover valve closed). Same idea — a dual-seal redundancy with manual changeover and no support equipment — but the default seal and the changeover action are reversed. Don't mix them up.

8. Retraction and extension — forward, with airflow assist

Retraction. Per AMM 32-21-00:

Because the downlock actuator is more lightly loaded, it retracts first to release the downlock and then starts to fold the lock stay (against the tension of the downlock springs). The NLG actuator then retracts the NLG and folds the drag stay.

Same pattern as the MLG: the downlock releases first, the lock stay and dragstay fold, the actuator raises the leg. The shock absorber has extended and the centering cam has straightened the wheels before retraction, so a straight wheel goes into the bay.

Extension. Per AMM 32-21-00:

The uplock opens to release the nose landing gear. Because the area of the piston on the extension side of the NLG actuator is more than the area of the retraction side, it extends the nose landing gear. The NLG actuator, the airflow and its own weight make the NLG extend.

Note the airflow: the NLG retracts forward, so on extension it swings forward and down into the relative wind, which helps push it open. This is the natural bonus of forward retraction — even with weak hydraulics or a gravity extension, the oncoming air lends a hand. Once down, the dragstay and lock stay open overcentre and the downlock springs hold the lock.

Self-test

[!note]- Q1. Why is the NLG shock absorber two-stage, and how do the stages share the load for small versus large impacts?

For a progressive stiffness one strut cannot get from a single stage. A floating piston splits the gas into two chambers, charged to different pressures (first stage ~12 bar, second stage ~55 bar). Light loads (taxi bumps) compress mainly the soft first stage for a smooth ride; heavy loads (a hard landing) compress into the stiff second stage to absorb the large impact. Soft for small, stiff for large.

[!note]- Q2. After lift-off, what realigns the nose wheels straight, and what second function does that part serve?

The upper and lower centering cams between the sliding tube and inner tube. As the absorber extends off the ground, their ramps slide against each other and rotate the sliding tube (and wheels) back to centre. They also act as a travel stop for the shock absorber. Together with the BSCU inhibiting steering once the absorber is fully extended, the wheel is both centred and steering-inhibited off the ground.

[!note]- Q3. The NLG torque links do one more job than the MLG's. What is it, and trace the steering path through them?

They transmit steering. The NWS steering actuators turn the rotating sleeve on the main fitting; the torque links carry that rotation to the sliding tube; the sliding tube twists the nose wheels. So the torque links are both the anti-rotation alignment member and the steering drive — one pair, two jobs.

[!note]- Q4. The NLG gets an extension aid the MLG does not. What is it, and why does only the NLG have it?

Airflow. The NLG retracts forward, so on extension it swings forward and down into the relative wind, which helps push it open and down. The MLG retracts inboard and gets no comparable airflow assist. This is why a forward-retracting nose gear is robust on a gravity extension — the oncoming air helps even without hydraulics.

[!note]- Q5. Compare the downlock spring redundancy of the MLG and NLG. How many springs, and how many remain enough after one fails?

The MLG has four downlock springs and three are sufficient if one fails. The NLG has two and one is sufficient if one fails. The NLG margin is tighter, but both remain single-fault-tolerant, so a gravity extension still locks down reliably on either gear.

Key takeaways

References

A330 specifics per FCOM DSC-32-10-10 (NLG configuration — twin wheels, oleo strut + NWS, forward retraction) and AMM 32-21-00 (Nose Gear — description and operation: trunnion/keel-beam mounting, two-triangle main fitting, two-stage oleo with floating piston / two gas chambers / metering tube / diaphragm / plate valve, centering cam, torque links carrying steering, dragstay/lock stay overcentre with two springs, dual-seal changeover, retraction/extension with airflow assist, uplock roller). The NLG structure diagram is an integrative synthesis of the AMM assembly figure and the AMM text, not a redraw of a single source figure. Numerical values (charge pressures, stroke) are collected in the Landing Gear Overview; nosewheel steering control is in Nosewheel Steering.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.