Eight Per Cent for Nine Kilometres

What has happened: you are in brake fade. Holding the service brakes on continuously down a long grade converts the truck's energy into heat faster than the drums and linings can shed it. The linings have heated past their effective operating range, so friction has dropped away - the pedal feels normal because the hydraulic side is fine, but the truck is not decelerating. Meanwhile you are still on a descent, so the speed climbs.

Next 30 seconds, in order:

1. Select a lower gear now - engine braking is unaffected by hot wheel brakes, and dropping a gear or two is the only retardation you can still add.
2. Apply the brakes firmly enough to actually shed speed while they still have some effect, rather than continuing a light continuous application.
3. Warn others - hazard lights, horn if needed - because your stopping ability is compromised and the car in front is braking.
4. Aim for the arrestor bay 600 m ahead. Do not gamble that the brakes will recover before the next corner. If the speed is still climbing as you reach it, use it.
5. Do not coast in neutral, and do not turn the engine off - you lose engine braking, retarder, and power steering.

If the speed is still rising: keep the gear low, keep the hazard lights on, and put the truck into the arrestor bay. A damaged truck in a gravel bed is a good day; a runaway truck is not.

What went wrong: the gear was only good enough to hold 50 km/h on the engine brake on its own. That is not the test. The test is whether the gear holds the truck at the signed descent speed with the service brakes untouched and a margin in hand. The moment you touched the brakes for the car, you were relying on the one system you had no spare capacity in, for a sustained period, on an 8% grade.

Better approach at the top:

• Select a gear before the descent that holds the truck at or below the signed speed on engine braking alone, with revs in the safe band and something in reserve.
• Use snub braking if the service brakes are needed: a firm application to pull the speed down well below the target, then off the pedal so the brakes cool, rather than riding them.
• Use the retarder if fitted, and know how it interacts with the engine brake.
• Check brake adjustment, air pressure and load security before starting the descent, and confirm the actual mass - an extra tonne changes everything.
• Plan for the descent being blocked by a slow vehicle: assume you may need to stop or slow sharply, and choose a speed you could actually stop from.

The key point: on a long descent, the gear is the primary speed control and the brakes are the backup. If you have it the other way around, you run out of the backup.

Stopping distance: a 14,500 kg rigid on an 8% downhill grade needs far more distance than the car in front of you - mass, gradient and heat all work against you, and by this point your brakes are already degraded. The gap you would accept on flat road at 60 km/h is not a gap on this grade.

Managing the gap:

• Hold at least a 4-second gap in good conditions, and add time for the descent, the load and the fading brakes - 5 or 6 seconds is not excessive here.
• If the car closes the gap by braking, reduce your own speed so the gap reopens. You cannot create space by hoping the brakes will hold.
• Keep the speed low enough that you could stop if the car stopped completely; on a grade like this that means being well under the signposted limit.
• Do not overtake or change lanes to escape the situation on a descent with compromised brakes - hold the lane, keep the gap, and use the arrestor bay if you need to get off the road.

The judgement: the car driver created the problem, but the consequence lands on you. Once you have fade, the only thing you control is speed and space, so you give away speed to keep space.