High Risk Work Licence - Slewing Mobile Crane C0 (over 100t) common mistakes
High Risk Work Licence - Slewing Mobile Crane C0 (over 100t) · Understand the traps and how to avoid them.
Treating the load chart as a static table and reading capacity for the boom length and radius only, without applying the configuration-specific deductions for jib, fly, auxiliary head, counterweight configuration, or outrigger spread actually in use.
Candidates memorise a single chart page and default to the main boom full-counterweight column, because that is the page they practised with; they do not build the habit of matching chart notes to the physical configuration on the day.
What to do instead
Before every practice lift, write out the configuration statement (boom length, jib fitted or not, counterweight set, outrigger spread, slew restriction) and then locate the chart page and notes that match it. Practise reading the notes column aloud and stating which deductions apply before quoting any capacity.
Calculating the lift radius from the crane's slew centre to the load instead of to the load's centre of gravity at the point of the boom tip, and measuring at ground level rather than at the boom head.
Ground-level tape measurement is easier and the load's near edge is visually obvious, so candidates underestimate radius; the error grows with jib offset and high boom angles where the tip sits well inboard of the load.
What to do instead
Use the load's centre of gravity, not its edge, and measure radius at boom-head height. Practise with the load chart's radius definition and verify with the crane's rated capacity limiter readout, treating any disagreement as a stop-and-recheck trigger.
Accepting the ground bearing pressure as adequate without checking outrigger pad size against the actual surface, and without considering underground services, voids, backfilled trenches, or recently disturbed ground.
Candidates focus on the crane's own stability and forget that the outrigger load is transferred into the ground; they also assume a hardstand is uniform when part of it may be a service trench cover.
What to do instead
Work through a set-up checklist: outrigger load per pad from the manufacturer's data, pad size and matting, surface type and bearing capacity, service drawings, and a physical inspection of the whole footprint. State the assumed bearing capacity and how it was confirmed.
Planning a multi-crane lift by splitting the load weight equally between cranes without accounting for load share changing as the load tilts, the centre of gravity shifts, or one crane takes up before the other.
Equal-share arithmetic is simple and feels fair, so candidates stop there; they do not visualise the rigging geometry change during the tilt or the effect of a single crane's hoist starting first.
What to do instead
For tandem lifts, calculate the share at the worst-case attitude, not the start attitude, and add a margin for dynamic and unequal take-up. Nominate one crane as lead, define the load-share limit for each, and require a documented lift plan with a hold point before the load leaves the ground.
Rigging the load with sling angles estimated by eye and a shackle or sling selected by 'looks big enough' rather than by working load limit against the calculated tension in each leg.
Candidates know the SWL is printed on the sling but do not convert the included angle into leg tension, and they confuse the tag rating with the tension the leg actually carries.
What to do instead
Practise the leg-tension calculation for 30, 45, 60 and 90 degree included angles until the multipliers are automatic, then select each component against that tension. State the angle, the multiplier, the tension and the chosen WLL out loud before rigging.
Treating the hazard identification as a generic list copied from a template, with no site-specific controls, no owner and no verification that the control was actually in place.
Risk assessment is often learned as a paperwork exercise for assessment, so candidates reproduce standard wording rather than reasoning from the actual task, plant and environment in front of them.
What to do instead
Build the assessment from the lift sequence: for each step, name the specific hazard, the consequence, the control, who verifies it and how. Include at least one hazard unique to the scenario given, and state the residual risk after the control.
Giving hand signals, radio calls or whistle signals that are not the standard agreed set, or continuing a lift when the signal source is ambiguous or two people are signalling.
Candidates focus on the crane operation and treat communication as background; under pressure they improvise signals or accept a shouted instruction from an unidentified person.
What to do instead
Memorise the standard signal set and the rule that only one nominated dogger signals, with the emergency stop signal available to anyone. In practice, call a stop whenever the signal is unclear or duplicated, and confirm the radio channel and call signs before the lift.
Describing pre-start inspection as a walk-around glance, omitting function checks of the rated capacity limiter, limit switches, slew and travel brakes, outrigger holding valves and the anti-two-block device.
The visual check is memorable and quick; the functional checks require knowing what each device does and how to prove it works, which candidates often have not practised.
What to do instead
Use a written inspection sequence covering structure, ropes, hooks and latches, then each safety device with the pass criterion stated. Practise stating what a failed anti-two-block or RCL test means: the crane is out of service and the defect is reported before any lift.
Responding to a powerline or contact incident by staying in the cab and continuing, or by jumping clear without keeping the feet together, and not establishing an exclusion zone around the crane.
Candidates recall 'stay in the cab' but not the conditions, the step-potential rule for exiting, or the need to keep others away; the sequence is learned as isolated facts rather than a procedure.
What to do instead
Rehearse the sequence: stop, warn others away, remain in the cab unless fire forces exit, if exiting jump clear and shuffle away with feet together, then establish the exclusion zone and notify. State who is called and in what order.
Parking and shutting down by lowering the load and switching off, without retracting or stowing the boom per the manufacturer, applying the slew lock or park brake, chocking, isolating the battery, and completing the log and handover.
Shutdown is treated as the end of the task rather than part of it, so the checklist is skipped once the lift is complete and the candidate relaxes.
What to do instead
Use a fixed shutdown checklist in order: land and secure the load, stow boom and jib, apply slew and park brakes, retract outriggers fully, chock, isolate, lock, record defects and handover notes. Practise reciting it in sequence until it is automatic.