On machines that use them, outriggers and stabilisers are what turn a mobile chassis into a stable platform. They plant the machine, spread its footprint and carry the reaction loads that keep it from tipping when the boom reaches out. A failure in this system — a jack that creeps down, an interlock that lets the boom operate before the machine is set, or a mount that cracks under load — attacks stability directly, which is the one thing an elevated worker most depends on. This guide covers how outriggers fail, why their interlocks and sensing are safety-critical, how the ground they sit on matters and how failures are put right.
Symptoms of outrigger and stabiliser problems
Trouble in the outrigger system shows up as:
- A jack or outrigger that creeps or settles under load, letting the machine lose level while the boom is deployed.
- Outriggers that deploy slowly, unevenly, or will not extend or retract fully.
- Interlocks that allow boom operation before the outriggers are properly set, or that fail to sense correct deployment.
- A level or tilt sensing system that reads incorrectly or does not alarm when the machine is out of level.
- Cracks, distortion or wear in the outrigger legs, mounts, pins or the pads themselves.
What causes outrigger failures
- Hydraulic faults — worn jack seals or a leaking holding valve that lets an outrigger settle under load.
- Setting up on inadequate ground, so the pad sinks or the ground gives way and the footprint is lost.
- Missing or undersized packing under the pads, concentrating load and overstressing the leg, mount and ground.
- Wear and damage to the legs, pins, slides and pads from repeated deployment and knocks.
- Faults in the interlock and level-sensing circuits that are meant to prevent unsafe operation.
Why interlocks and level sensing are critical
The outrigger interlocks exist to enforce the correct sequence — the machine should not let the boom work until it is properly set on its outriggers, and it should warn or intervene if the machine goes out of level. These are safety systems in the truest sense: they stop an operator from putting the boom out over an unstable base.
Because of that, an interlock or level-sensing fault is never something to bypass or work around. A system that lets the boom operate before the machine is set, or that fails to alarm when it is out of level, removes the very protection against a tip-over. These devices are function tested by a competent person, and a fault takes the machine out of service.
The ground the machine sits on
An outrigger is only as good as what it stands on. Even a perfect outrigger system will fail if the pad is set on ground that cannot carry the load, on a service cover, or against an unseen void. This is why set-up is an operator responsibility that no amount of machine condition can substitute for.
Correct, adequately sized packing spreads the load onto the ground, and assessing the ground before setting up — its bearing capacity, slope and hidden hazards — is part of siting the machine safely under AS 2550.10. A settling outrigger is sometimes a hydraulic fault and sometimes simply the ground giving way, and telling the two apart is part of a proper assessment.
How outrigger failures are repaired
- Take the machine out of service so it is not set up on a system with a known fault.
- Diagnose the cause — reseal or repair the jack, renew the holding valve, or repair the interlock or sensing circuit as the fault dictates.
- Crack test and repair or replace cracked or distorted legs, mounts and pins as engineered structural work.
- Restore any safety setting or calibration on the level and interlock systems to specification.
- Function test deployment, holding under load, interlocks and level sensing, then record the work in the logbook.
Preventing outrigger failures
Good practice divides between the machine and the set-up. On the machine, maintaining the jack seals and holding valves prevents settling, and keeping the interlock and level circuits sound keeps the protection working. On site, assessing the ground and using correct packing under every pad is what actually delivers the stable footprint the machine is designed to give.
An outrigger that settles, an interlock that misbehaves, or a level system that reads wrong is a reason to park the machine and get a competent person onto it — call EWP Australia on 0416 689 689 to book an assessment rather than risk working from an unstable base.
This guide is general information prepared by EWP Australia and is grounded in publicly available Australian Standards and Safe Work Australia material. It is not a substitute for the current published edition of the relevant standard or for site-specific engineering advice. Always work from the current standard and consult a competent person for your specific equipment and application.