Steering Faults

Loss of nosewheel steering (NWS) is not a single fault — several paths reach the same result, and each leaves a different set of capabilities. This article sorts them out, then covers how to get the aircraft back without NWS, and one key prohibition: a braked pivot turn is forbidden.

 Three paths to losing NWS          What remains?
 ─────────────────────────         ─────────────
 (1) green pressure lost (A/SKID & NWS still ON) ─► antiskid ✓ (blue takes over) · differential braking ✓ · NWS ✗ · triple indicator shows blue
 (2) A/SKID & N/W STRG = OFF ──────► antiskid ✗ (manual pressure limit) · differential braking ✓ (pedals) · NWS ✗ · triple indicator shows blue
 (3) BSCU fault (N/W STRG FAULT) ──► castoring (free-caster nose wheel) · differential braking ✓ (if braking is normal) · NWS ✗
 (4) after gravity extension (article 19) ─► green isolated · NWS ✗
                                          │
                          direction: high speed → rudder (authority falls with speed); low speed → differential braking
                          ⚠️ a braked pivot turn is prohibited (differential braking must not fully stop one main gear)
                          unfamiliar with differential braking → request a tow; triggered in flight → request it early

1. Each path leaves something different (the key distinction)

The FCOM is clear on the two key states of the A/SKID & N/W STRG switch. Per FCOM DSC-32-30-20:

ON: If green hydraulic pressure is lost: Blue hydraulic pressure automatically takes over to supply the brakes / Antiskid remains available / Nose wheel steering is lost / Brake blue pressure is displayed on the triple indicator.

And: OFF: Blue hydraulic pressure supplies the brakes: Antiskid is deactivated. Brake pressure has to be limited by the pilot... Nose wheel steering is lost / Differential braking remains available by pedals / Brake blue pressure is displayed on the triple indicator.

The distinction:

• Green lost (switch still ON): NWS is lost, but antiskid remains (alternate with antiskid — Alternate Braking) — the braking experience is relatively good.
• A/SKID & N/W STRG OFF: NWS lost and antiskid lost (alternate without antiskid), braking must be manually limited — this is the state after a LOSS OF BRAKING (Brake Failure and Degradation).
• Both keep differential braking (on the pedals) — the lifeline for holding direction without NWS.
• N/W STRG FAULT (a BSCU fault): as in Nosewheel Steering, the nose wheel goes to castoring (free-caster), the E/WD shows N/W STRG FAULT and the WHEEL page shows N.W. STRG amber.

2. Holding direction without NWS

Per FCTM PR-AEP-LG:

If the NWS is lost for taxiing, the flight crew can steer the aircraft with differential braking technique. If the flight crew does not have experience with this technique, the flight crew should preferably request a towing to return to the gate. The flight crew can request the towing early in approach, if the failure has been triggered in flight.

By speed band:

• High speed (landing roll): hold direction with the rudder — but as Brake Failure and Degradation noted, rudder authority falls with speed and becomes less useful the slower you go.
• Low speed (taxi): differential braking (braking one side to help turn) plus asymmetric thrust.
• Tow back: differential braking is a skill; if unfamiliar, prefer a tow. If the fault was found in flight, arrange it early rather than getting stuck mid-taxi.

3. A key prohibition — no braked pivot turn

Per FCOM LIM-LG:

Braked pivot turn is prohibited (ie. differential braking cannot be used to fully stop one main gear).

Reading the prohibition: differential braking can brake one side harder to help a turn, but you must never fully lock one main gear and pivot the aircraft around it — this puts an enormous torsional load on that side's tyres/gear structure (the tyre is twisted in place, not rolling) and can damage it. Differential braking assists a turn; it does not pivot about an axle. This is the limit most easily violated when taxiing on a failed NWS.

4. N/W STRG FAULT versus a deliberate OFF

Recalling Nosewheel Steering: N/W STRG FAULT (E/WD) is a BSCU-detected fault (not crew-selected) → castoring + amber. A/SKID & NWS OFF (E/WD shows A/SKID & NWS OFF) is a deliberate switch-off (which also turns off antiskid). Both lose NWS, but the former is a passive fault and the latter a deliberate choice (and the latter loses antiskid too). Read the ECAM text to tell them apart.

[!warning]- Five misconceptions this article corrects (1) Losing NWS does not always lose antiskid — with green lost and the switch ON, antiskid remains; only OFF loses it too. (2) Losing NWS does not leave you unable to steer — differential braking plus the rudder still hold direction. (3) Differential braking may not be used to lock one wheel and pivot in place — a braked pivot turn is prohibited (it damages the tyre/gear). (4) Differential braking is not for everyone — if unfamiliar, prefer a tow; arrange it early for an in-flight fault. (5) N/W STRG FAULT and a deliberate OFF are not the same — FAULT is a passive failure; OFF is a deliberate switch-off that also loses antiskid.

Self-test

[!note]- Q1. What remains on each of the three NWS-loss paths?

Green lost with the switch ON: antiskid remains, differential braking remains, NWS lost. A/SKID & N/W STRG OFF: antiskid lost, differential braking remains, NWS lost. BSCU fault (N/W STRG FAULT): nose wheel castors, differential braking remains (if braking is normal), NWS lost.

[!note]- Q2. How is direction held without NWS, high speed versus low speed?

High speed (landing roll): the rudder, though its authority falls with speed. Low speed (taxi): differential braking (braking one side to help turn) plus asymmetric thrust. If the technique is unfamiliar, request a tow.

[!note]- Q3. Why is a braked pivot turn prohibited?

Because fully locking one main gear to pivot around it puts an enormous torsional load on that side's tyres and gear structure (the tyre is twisted in place rather than rolling), which can damage it. Differential braking assists a turn; it does not pivot about an axle.

[!note]- Q4. What should a crew unfamiliar with differential braking do?

Prefer to request a tow back to the gate. If the fault was triggered in flight, request the tow early in the approach rather than attempting to taxi and getting stuck.

[!note]- Q5. What is the difference between N/W STRG FAULT and A/SKID & NWS OFF?

N/W STRG FAULT is a BSCU-detected fault (not crew-selected) that puts the nose wheel into castoring with an amber indication. A/SKID & NWS OFF is a deliberate switch-off, which also turns off antiskid. Both lose NWS; the difference is passive fault versus deliberate choice (and the OFF loses antiskid too).

Key takeaways

References

A330 procedures per FCOM DSC-32-30-20 (the A/SKID & N/W STRG switch states — green-lost-with-ON keeps antiskid and NWS lost, OFF loses NWS and antiskid with differential braking remaining, the triple indicator), FCTM PR-AEP-LG (NWS lost for taxiing — differential braking technique, request a tow if unfamiliar, request it early for an in-flight fault), FCOM LIM-LG (the braked-pivot-turn prohibition), and AMM 32-51-00 (N/W STRG FAULT indication and castoring, via Nosewheel Steering). The three-path diagram is an integrative synthesis of the FCOM/FCTM text and the castoring mechanism. The detailed differential-braking technique is SME/simulator experience; the full N/W STRG FAULT ECAM steps are in ECAM Warning Family.

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.