Mobile Crane Operator Flashcards

A mobile crane is rigging a 42,000 lb load at a 60-foot radius. The load chart shows a capacity of 48,000 lbs at 60 feet, but the boom is currently set at 72° from horizontal and the load line is two-blocked. The operator should FIRST:

Answer: Lower the load to the ground before correcting the two-block condition

A two-block condition means the upper and lower load blocks have come together, creating a risk of parting the hoist line or dropping the load. The safest immediate corrective action is to lower the load to the ground (by carefully booming down or paying out hoist line if slack allows) so the two-block condition can be resolved safely. Raising the boom would worsen the condition and increase the risk of line failure.

During a pick-and-carry operation with a rough-terrain crane, the operator must travel over a surface with an 8% cross-slope. The crane's rated capacity for travel is 85% of its static rated capacity. Which action is MOST appropriate?

Answer: Assess whether the load weight and slope together exceed the travel tipping limit before proceeding

Before attempting pick-and-carry on any cross-slope, the operator must evaluate whether the combination of the load weight, boom angle, and side slope places the resultant force outside the tipping fulcrum. An 8% cross-slope significantly reduces effective capacity. Simply slowing down or repositioning the boom does not address the fundamental stability calculation required by ASME B30.5 and the crane's load chart footnotes for travel.

A lattice-boom crawler crane is rigged with a luffing jib at 40° offset. The main boom is 200 feet and the jib is 60 feet. When reading the load chart for this configuration, which combination of values must BOTH be confirmed before lifting?

Answer: Main boom capacity at the working radius AND jib capacity at the jib tip radius

When operating with a luffing or fixed offset jib, the load chart provides two separate rating tables: one for the main boom at the jib's heel radius and one for the jib tip at its working radius. Both limits must be satisfied simultaneously — the load must not exceed either the main boom's capacity at the effective radius or the jib's rated tip load. Checking only one of the two tables is a common and dangerous error.

An operator is performing a critical lift with a hydraulic truck crane. Midway through the lift, the load moment indicator (LMI) alarm activates at 90% of rated capacity. The operator had confirmed the load weight and radius before beginning. Which of the following is the MOST likely cause that the operator should investigate?

Answer: A slight outrigger pad settlement has changed the effective working radius

Outrigger pad settlement — even a fraction of an inch — causes the crane to tilt, which increases the effective working radius beyond the planned radius. This directly reduces the available rated capacity. LMI systems measure actual load moment (load × radius) and will alarm if the radius grows. This is one of the most common field scenarios that catches operators off guard during long lifts on soft or uneven bearing surfaces.

Under OSHA 1926.1416, a mobile crane's load line hoist rope must be removed from service if which of the following conditions is found during inspection?

Answer: A 6% reduction in nominal rope diameter from the original diameter

OSHA 1926.1416 and ASME B30.5 specify that a rope with a reduction in nominal diameter of more than 5% from its nominal diameter must be removed from service. A 6% reduction exceeds this threshold. The broken wire criterion for a 6×19 rope is six randomly distributed broken wires in one lay (not three), and minor surface corrosion or isolated heat discoloration does not automatically require removal but does require closer inspection.

A mobile crane operator is working in a congested urban site. The signal person gives a 'stop' signal, but a split-second later the lift director verbally orders 'keep hoisting' over the radio. According to ASME B30.5 and NCCCO standards, the operator should:

Answer: Stop the operation immediately and await clarification before resuming

ASME B30.5 and NCCCO protocols are unambiguous: a 'stop' signal from any authorized signal person must be obeyed immediately regardless of who issues it or what other instructions are received. The operator must stop and must not resume operation until the conflict between signals is resolved and a clear, unambiguous directive is received. In a conflict between a stop signal and any other command, the stop signal always takes precedence.