Mobile Crane Operator 4 Flashcards

A mobile crane is rigging a 40-ton load using a four-leg bridle sling with legs at 60° from horizontal. Two legs are rated at 25 tons each and two are rated at 20 tons each. The load is unevenly distributed so that 60% of the weight bears on the two 20-ton legs. What is the tension in each of the 20-ton legs?

Answer: 13.86 tons

60% of 40 tons = 24 tons shared between the two 20-ton legs. Tension per leg = (24/2) ÷ sin(60°) = 12 ÷ 0.866 = 13.86 tons. The sling angle factor divides the vertical load component, increasing actual leg tension above the simple share of the load.

During a critical lift, the crane operator notices the load line is bearing laterally against the boom nose sheave rather than tracking in the sheave groove. Which condition MOST LIKELY caused this, and what is the immediate corrective action?

Answer: The load has shifted off-center; reposition the crane so the load hangs directly below the boom point before resuming the lift

Side loading of the boom nose sheave is a direct indicator that the load is not hanging plumb beneath the boom point, creating a lateral force component. The correct action is to reposition the crane to achieve a plumb lead before continuing. Fleet angle violations and sheave wear are separate issues — and increasing line speed never corrects sheave tracking.

According to ASME B30.5, when is it permissible for a mobile crane operator to leave the operator's station with a load suspended?

Answer: Never — the operator must remain at the controls whenever a load is suspended

ASME B30.5 is unambiguous: the operator shall not leave the operator's station while a load is suspended. There are no capacity-percentage exceptions, lift director approval exceptions, or clearance exceptions that override this prohibition. Leaving the controls with a suspended load is a major safety violation regardless of load weight.

A hydraulic telescoping boom crane is operating at 72% of its rated capacity on outriggers when the operator observes a 3% drop in hydraulic system pressure while holding the load stationary. What should the operator do FIRST?

Answer: Lower the load to the ground under controlled power immediately and shut down to inspect the hydraulic system

A pressure drop in a loaded hydraulic system signals a potential failure — leak, pump degradation, or valve issue — that could result in uncontrolled load movement. The correct first action is to lower the load in a controlled manner using available power before the system deteriorates further. Retracting the boom with a live load at height, switching circuits, or revving the engine do not address the root cause and increase risk.

A crane is completing a tandem lift when one crane's load cell reads 15% higher than its pre-calculated share. The lift director instructs the operators to hold position while the rigging is inspected. While holding, the overloaded crane's boom angle is 72° and the other crane's is 68°. What does the discrepancy in load cell readings MOST likely indicate?

Answer: The load's center of gravity is offset toward the overloaded crane, causing unequal load distribution despite equal hook heights

In a tandem lift, an unexpected overload on one crane almost always means the load's actual center of gravity differs from the assumed position, placing more weight toward that crane. The 4° boom angle difference alone does not create a 15% load shift — both cranes are vertically supporting the load, not acting as a lever. A faulty load cell is possible but is not the most likely cause; a CG offset is the standard explanation that lift plans must address.

Under OSHA 1926.1416, which of the following deficiencies found during a shift inspection requires the crane to be IMMEDIATELY removed from service, with NO operation permitted until repaired?

Answer: A load line with 3 broken wires in one lay length in the running portion

ASME B30.5 and OSHA 1926.1416 mandate immediate removal from service for running wire rope with broken wires exceeding the threshold — typically 3 broken wires in one lay length for mobile crane load lines. This is a bright-line rule requiring no further judgment. Hydraulic fluid level, pad surface cosmetic cracks, and intermittent LMI alarms are serious but do not trigger an absolute immediate out-of-service requirement in the same regulatory language.