NCCCO Telescoping Boom and Jib Configuration 1 — Questions and Answers
Question 1: Before extending a telescoping boom section, the operator must first ensure the boom is:
- At maximum elevation angle
- Fully lubricated at all pivot points
- Free of any suspended load (Correct answer)
- Operating at full engine RPM
Correct answer: Free of any suspended load
Telescoping a boom under load is prohibited unless the manufacturer's documentation specifically permits it, because the load moment changes as the radius increases.
Question 2: When a mobile crane's telescoping boom is extended to a longer length, the rated lifting capacity will:
- Increase proportionally with boom length
- Remain unchanged for all boom lengths
- Only change if a jib is also attached
- Decrease as the increased radius increases the load moment (Correct answer)
Correct answer: Decrease as the increased radius increases the load moment
Extending the boom increases the working radius, and since load moment equals load multiplied by radius, the rated capacity decreases to stay within structural limits.
Question 3: The fly jib 'offset angle' on a mobile crane refers to:
- The angle the main boom makes with the ground
- The horizontal swing arc of the jib
- The angle between the jib and the main boom centerline (Correct answer)
- The maximum elevation angle of the jib tip
Correct answer: The angle between the jib and the main boom centerline
Offset angle is the angle formed between the centerline of the jib and the centerline of the main boom, and separate load charts exist for each rated offset angle.
Question 4: What is the primary purpose of a fly jib (boom extension) on a mobile crane?
- To increase the maximum rated lifting capacity
- To extend the crane's reach in height or radius beyond the main boom (Correct answer)
- To reduce overall boom assembly weight
- To allow operation without deployed outriggers
Correct answer: To extend the crane's reach in height or radius beyond the main boom
A fly jib adds length beyond the main boom tip, allowing the crane to reach greater heights or radii that the main boom alone cannot achieve.
Question 5: When using a jib attachment, which load chart must the operator reference?
- The main boom chart at full extension
- The standard rigging chart for the hoist line
- Any chart showing a capacity above the required load
- The jib-specific chart for the exact jib length and offset angle being used (Correct answer)
Correct answer: The jib-specific chart for the exact jib length and offset angle being used
Each jib length and offset angle combination has its own rated capacities; using any other chart would result in an unsafe or incorrect capacity determination.
Question 6: Mechanical locking pins on telescoping boom sections are critical because they:
- Increase hydraulic cylinder pressure during extension
- Prevent the boom from rotating on the turntable
- Secure the boom section in position if hydraulic pressure is lost (Correct answer)
- Are only required for lifts exceeding 50% of rated capacity
Correct answer: Secure the boom section in position if hydraulic pressure is lost
Hydraulic systems can lose pressure due to seal failure or line damage; mechanical pins prevent catastrophic boom retraction under load if pressure is lost.
Question 7: Before operating with a newly assembled jib configuration, an operator must verify that:
- The jib color matches the manufacturer's specification
- All connecting pins are fully inserted, secured, and properly cottered (Correct answer)
- The jib has been tested at 110% of rated capacity
- A licensed engineer has approved the jib configuration
Correct answer: All connecting pins are fully inserted, secured, and properly cottered
Improperly secured connecting pins can allow the jib to separate from the boom tip during a lift, causing catastrophic failure.
NCCCO Telescoping Boom and Jib Configuration 1
Before extending a telescoping boom section, the operator must first ensure the boom is: