NCCCO Tower Crane Operator Test 1 3 — Questions and Answers
Question 1: What is the purpose of the moment limiting device (MLD) on a hammerhead tower crane?
- To limit the maximum rotational speed of the slewing ring
- To automatically reduce trolley travel speed as the crane approaches rated load moment, and cut off functions when rated moment is reached at any radius (Correct answer)
- To prevent the crane from being used during high winds by sensing overturning moments
- To equalize torque between the crane's multiple hoist motors
Correct answer: To automatically reduce trolley travel speed as the crane approaches rated load moment, and cut off functions when rated moment is reached at any radius
The moment limiting device monitors the load moment (load times radius) continuously and cuts off crane functions, particularly trolley travel out and hoisting, when the combination of load weight and radius would exceed the rated moment for the crane's current configuration.
Unlike simple load limiters that only monitor hook load, the moment limiting device calculates the actual load moment by combining the measured load weight with the trolley's current radius position. This allows the crane to carry heavier loads at short radii (where the moment is low) while automatically limiting the trolley's outward travel as the rated moment is approached. When moment reaches 100% of rating, trolley-out motion and hoisting are cut off. The MLD must be calibrated for the specific jib length and ballast configuration in use, making pre-shift configuration verification essential for proper MLD function.
Question 2: What is the procedure for performing a 'no-load' check before the first lift of the day on a tower crane?
- A no-load check is not required; functional tests are only needed after maintenance
- Raise the empty hook block to a moderate height and test each crane motion function to verify proper operation before any loaded lifts are made (Correct answer)
- Test only the emergency stop and hoist brake; other functions do not require daily testing
- No-load checks are performed weekly during scheduled maintenance periods
Correct answer: Raise the empty hook block to a moderate height and test each crane motion function to verify proper operation before any loaded lifts are made
A no-load functional check tests all crane motions (hoisting, slewing, trolley travel) with the empty hook to verify all systems respond correctly before a load is applied, catching any malfunctions in a low-consequence situation.
No-load functional checks allow operators to identify control malfunctions, unusual mechanical sounds, and limit switch issues before a load is suspended. Testing each motion (hoist up/down, slew left/right, trolley in/out) verifies motor direction, brake engagement and release, limit switch activation at proper positions, and absence of unusual noises suggesting mechanical problems. Issues found during no-load checks can be corrected without the added risk of a suspended load. After completing no-load testing, the operator should also verify that all limit switches are functional by approaching (not activating) them during the test.
Question 3: What is the correct procedure when a tower crane load indicator shows the lift is near maximum rated capacity?
- Increase hoisting speed to complete the lift quickly before conditions change
- Slow all crane movements, increase caution, avoid simultaneous multi-axis motions, and verify the actual load weight before proceeding with the planned lift (Correct answer)
- Near-capacity lifts are treated identically to light lifts with no special procedures
- Pause operations and wait for a shift supervisor to authorize the lift
Correct answer: Slow all crane movements, increase caution, avoid simultaneous multi-axis motions, and verify the actual load weight before proceeding with the planned lift
Near-capacity lifts require extra caution: slowed movements to reduce dynamic loads, single-axis motion to minimize combined stresses, and verification that the indicated load weight matches documented load weight before proceeding.
At near-capacity loads, the margin between rated capacity and actual tipping/structural load is at its minimum design value. Any additional dynamic load from rapid motions, wind effects, or simultaneous multi-axis crane movements can push the total load moment beyond the rated value. Operators must reduce all motion speeds to minimize dynamic amplification, avoid simultaneous hoisting and slewing that creates combined loading, verify the actual load weight against documentation, and briefly suspend the load just off the ground before performing the full lift to confirm the load indicator reading is consistent with the known load weight.
Question 4: What should a tower crane operator do if they experience a sudden uncontrolled slewing movement while operating?
- Apply maximum braking to stop rotation as quickly as possible
- Gently apply slewing counter-motion to slow the rotation while simultaneously lowering the load toward the ground, and then stop crane operations to investigate the cause (Correct answer)
- Continue operating and alert maintenance to the issue at shift end
- Immediately abandon the cab using the emergency descent device
Correct answer: Gently apply slewing counter-motion to slow the rotation while simultaneously lowering the load toward the ground, and then stop crane operations to investigate the cause
Uncontrolled slewing requires gentle braking with counter-slew while lowering the load, avoiding abrupt stops that could snap wire rope, then ceasing operations to identify the mechanical cause before resuming.
Uncontrolled slewing (runaway rotation) can be caused by slewing brake failure, control valve sticking, or counterweight imbalance after configuration changes. Abrupt application of maximum braking creates shock loads in the wire rope, rigging, and slewing ring that can cause failures more catastrophic than the controlled rotation. Gentle counter-slew braking reduces rotation speed gradually while simultaneously lowering the load toward the ground reduces the potential consequence of any load drop. Once the load is safely on the ground, the crane must be taken out of service and the cause of the uncontrolled movement identified and corrected by qualified maintenance personnel.
Question 5: Why must a tower crane operator monitor the load's behavior immediately after picking it up from the ground?
- Ground observation allows the operator to assess rigging color coding compliance
- Observing the load just after pickup allows the operator to identify load shift, rigging imbalance, or unexpected weight before committing to the full lift path (Correct answer)
- Monitoring after pickup is only required for critical lifts over 75% capacity
- Only the signal person needs to monitor the load; the operator focuses on controls
Correct answer: Observing the load just after pickup allows the operator to identify load shift, rigging imbalance, or unexpected weight before committing to the full lift path
Lifting the load just clear of the ground and holding it briefly allows identification of rigging problems, unexpected weight, or load imbalance before the load is moved over workers or structures during the full lift path.
The moment a load leaves the ground is when rigging problems, unexpected weight, and balance issues become apparent. If the load hangs crooked, rigging attachment point assumptions were wrong. If the LMI reads higher than expected, the load weighs more than estimated. If a rigging component shows stress or the load swings, the attachment geometry is incorrect. Identifying these problems just off the ground, before traveling the load over workers, adjacent structures, or across the site, allows correction in the safest possible location. Tower crane procedures should require a brief pause just after liftoff to assess load behavior before executing the full lift plan.
Question 6: What is the responsibility of a tower crane operator when visibility to the load is blocked during any portion of the lift?
- Continue at reduced speed using radio communication as the primary guidance
- Stop crane movement immediately until a signal person with direct line of sight to the load is in position and communication is established (Correct answer)
- Rely on the LMI data to proceed without visual contact
- Continue the lift as planned as long as the landing zone is visible
Correct answer: Stop crane movement immediately until a signal person with direct line of sight to the load is in position and communication is established
OSHA requires that crane operators must not move loads without direct line of sight to the load or a qualified signal person with direct line of sight, as operation without visual contact of the load creates hazards for workers in the load path.
Tower cranes routinely operate in situations where parts of the lift path are obscured, such as loads passing behind structures, drops into trenches, or placements below grade. OSHA 29 CFR 1926.1419 requires that whenever the operator cannot see the load or any part of the operation area, a signal person must be stationed where they can see the crane, the load, and any hazards, and must maintain continuous communication with the operator. Operations must stop until this condition is established. Operating without visual contact and without a signal person creates conditions where workers in the blind zone cannot be protected from crane movements.
NCCCO Tower Crane Operator Test 1 3
What is the purpose of the moment limiting device (MLD) on a hammerhead tower crane?