Brake Failure and Degradation

This article collects the braking mechanisms of articles 08–13 into one failure-handling chain — how braking falls back, layer by layer, when it is lost. The core is the LOSS OF BRAKING memory item: when it should be used, the three-step sequence, and why the wrong order fails to recover. Per FCTM PR-AEP-BRK:

The [MEM] LOSS OF BRAKING enables the flight crew to manually activate the alternate braking mode without the antiskid function in the case of: A failure of the normal braking mode, and A failure of the automatic switching from normal braking mode to the alternate braking mode. Ultimately, if the alternate braking mode without antiskid fails, the [MEM] LOSS OF BRAKING requests the use of the parking brake to stop the aircraft.

 (1) Normal braking (green · antiskid · autobrake · servovalve metering)
     │ normal fails AND the automatic selector valve changeover also fails
     │ [if the changeover works → (2) takes over automatically; no memory item needed]
     ▼
 (2) Alternate with antiskid (blue · automatic changeover · paired antiskid · hydraulic pedals)  ← usually reached automatically; if you feel deceleration, leave it
     │ if even (2) is gone / never engaged
     ▼
 (3) ══ [MEM] LOSS OF BRAKING ══► Alternate without antiskid (A/SKID OFF · manual ≤ 1000 PSI)
     │  three-step sequence (order matters):
     │   1. release the brake pedals
     │   2. request the PM to set A/SKID & N/W STRG → OFF
     │   3. press the pedals only after OFF; modulate ≤ 1000 PSI
     │  consequence: lose antiskid AND nosewheel steering
     │ still no braking
     ▼
 (4) Parking brake (ultimate): short successive applications · delay to low speed · tyre-burst / lateral-control risk

1. When to use it — only when there is no deceleration

This is the easiest thing to get wrong — LOSS OF BRAKING is not for "braking feels weak". Per FCTM PR-AEP-BRK:

The [MEM] LOSS OF BRAKING must be applied only if the flight crew does not perceive any effect on the deceleration when applying manual braking.

Why "no deceleration at all" — the wet/contaminated runway has a big trap. Per FCTM PR-AEP-BRK:

On wet/contaminated runways... the pilot may feel the antiskid cycling with a small deceleration rate. As per design, the antiskid cycling leads from time to time to short periods of brakes release to avoid wheel locking... the undue application of the [MEM] LOSS OF BRAKING can affect the landing performance.

On a slippery runway the antiskid releases the brakes frequently (Antiskid) and the deceleration feels weak — but that is the antiskid working normally, not a brake failure. Doing LOSS OF BRAKING here, switching antiskid off, makes a lock and tyre burst more likely and the performance worse. (Likewise, do not misread the change in deceleration feel as reverse moves from MAX to IDLE.) The criterion is "no deceleration at all", not "not enough deceleration".

2. The three-step sequence — why release the pedals first

Per FCTM PR-AEP-BRK:

In order to successfully revert to alternate braking, it is important to sequence the actions in three steps. The PF should: 1. Release the brake pedals / 2. Request the PM to set the A/SKID & N/W STRG sw to OFF / 3. Press the brake pedals, only after the PM has set the A/SKID & N/W STRG sw to OFF. Modulate brake pedal pressure to maximum 1000 PSI.

Why release the pedals first (with the Alternate Braking mechanism): in alternate-without-antiskid the servovalves are fully open and the pedals feed pressure directly through the dual valve. If you switch A/SKID OFF while pressing, the changeover can deliver an uncontrolled pressure surge (even a lock). Releasing the pedals first lets the system change cleanly to alternate-without-antiskid at zero brake demand, then you re-apply — so pressure builds up controllably from zero. The wrong order (switching while pressing) means a changeover surge and a possible lock. The ≤ 1000 PSI follows because there is no antiskid — the pilot modulates manually to avoid a lock (Alternate Braking).

3. The extra cost — nosewheel steering goes too

Per FCTM PR-AEP-BRK:

The procedure... results in: The loss of the nosewheel steering: Aircraft directional control can only be ensured by means of the rudder at high speed... and differential braking (if recovered) / The loss of the antiskid function.

Why steering goes too — because A/SKID & N/W STRG is one switch over two functions (Nosewheel Steering / Steering Angle Protection): switching it OFF loses antiskid and nosewheel steering together. So after LOSS OF BRAKING, directional control becomes "rudder at high speed + differential braking at low speed" (Steering Faults). This is the hidden cost of the memory item, and it must be expected.

4. The parking brake as the ultimate brake — short, successive, delayed

Per FCTM PR-AEP-BRK:

If still no braking, use short successive parking brake applications to stop the aircraft / Brake onset asymmetry may be felt at each parking brake application / If possible, delay the use of parking brake until low speed, to reduce the risk of tire burst and lateral control difficulties.

Why "short, successive" rather than "pull it once and hold": the parking brake (Parking and Ultimate Emergency Braking) has no antiskid and runs on the accumulator (limited applications); pulling full pressure (175 bar) in one go locks the wheels and bursts tyres. Short pulses are a manual imitation of antiskid, giving the wheels a chance to spin back up. Delay to low speed because a high-speed lock and tyre burst, with the asymmetric onset, would cause severe lateral loss of control. This echoes the "≤ 1000 PSI, gentle and progressive" of Parking and Ultimate Emergency Braking.

Reverse thrust is an important decelerator here. Per FCTM PR-AEP-BRK: If needed, full reverse thrust may be used until coming to a complete stop. Below 70 kt... the flight crew should set idle reverse thrust... avoid the use of high level of reverse thrust at low speed in order to avoid engine stall and excessive EGT. Unlike the normal "stow reverse by 70 kt", a brake failure allows full reverse to a complete stop (trading some engine wear for stopping).

[!warning]- Six misconceptions this article corrects (1) Weak braking does not call for LOSS OF BRAKING — only no deceleration; weak deceleration on a wet runway is normal antiskid cycling. (2) The three-step order does not matter little — you must release pedals, then A/SKID OFF, then press; switching while pressing causes a surge/lock. (3) LOSS OF BRAKING does not lose only antiskid — it loses nosewheel steering too (one switch, two functions). (4) Pulling the parking brake once is not the fastest stop — short successive applications avoid a lock; delay to low speed. (5) A brake failure does not keep the 70 kt reverse-stow rule — full reverse may be used to a complete stop. (6) A normal automatic changeover does not need the memory item — alternate-with-antiskid takes over automatically; if you feel deceleration, leave it.

Self-test

[!note]- Q1. What is the only condition to apply LOSS OF BRAKING, and does weak deceleration on a wet runway count?

Only when applying manual braking produces no perceptible deceleration at all. Weak deceleration on a wet runway is normal antiskid cycling (the antiskid briefly releasing to avoid a lock), not a failure — applying LOSS OF BRAKING there would worsen performance.

[!note]- Q2. Give the three-step sequence and explain why the pedals are released first.

(1) Release the brake pedals, (2) request A/SKID & N/W STRG OFF, (3) press only after OFF, modulating ≤ 1000 PSI. Release first because in alternate-without-antiskid the servovalves are fully open and the pedals feed pressure directly; switching while pressing would deliver an uncontrolled surge or lock. Releasing first lets the changeover happen at zero demand, then pressure builds controllably.

[!note]- Q3. Give the four-layer degradation chain.

Normal (green, antiskid) → alternate with antiskid (blue, automatic changeover) → alternate without antiskid (A/SKID OFF, manual ≤ 1000 PSI, the memory item) → parking brake (ultimate). Each step loses a capability; antiskid and the electrical dependence step down through the chain.

[!note]- Q4. What does LOSS OF BRAKING lose besides antiskid, and how is direction then controlled?

It also loses nosewheel steering, because A/SKID & N/W STRG is one switch over both. Direction is then controlled by the rudder at high speed and differential braking at low speed.

[!note]- Q5. How is the parking brake used as the ultimate brake?

In short successive applications (a manual imitation of antiskid, to avoid locking on the no-antiskid, accumulator-fed parking brake), delayed to low speed where possible, to reduce the risk of tyre burst and lateral loss of control.

Key takeaways

References

A330 procedures per FCTM PR-AEP-BRK (LOSS OF BRAKING — general and procedure: apply only with no deceleration, the wet-runway antiskid-cycling trap, the three-step sequence, ≤ 1000 PSI, short successive parking-brake applications, full reverse to a stop, the loss of NWS and antiskid). The four-layer chain diagram is an integrative synthesis of the FCTM and the braking articles 08–13; the "why" of each step links to those system articles. The specific ECAM triggers (BRAKES SYS 1(2) FAULT, etc.) are in ECAM Warning Family; the EFB/performance quantification of LOSS OF BRAKING is performance-layer.

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.