Here’s 7 overlooked inspections on aerial devices and digger derricks

aerial lift inspections
By Duane Torgerson, National service technician at Terex

Owners of digger derrick and aerial devices are responsible for ensuring their equipment is inspected annually. This responsibility can mean more than just meeting requirements set by OSHA or ANSI. Thorough annual inspections are one of the key components to help ensure the equipment is safe for both the operator and crew members. 

While safety is the top priority, annual inspections can also reveal small operational issues before they cause serious, and possibly expensive, equipment repairs.

Annual inspections are a task to be performed by qualified people, such as Terex Utilities’ factory trained technicians who have access to the right tools to properly complete the task. Organizations with experienced service technicians may choose to perform and document these inspections in-house or outsource to a third party. 

When it’s time to conduct an annual inspection, expect the process to take three to six hours depending on the type of equipment being inspected.  It’s a good idea to schedule annual inspections strategically to help minimize downtime of your fleet.  Allow extra time for scheduled maintenance. Based upon the findings from the inspection, you may need to plan for additional required repairs to be performed.  For insulated aerial lifts and digger derricks, it is recommended the annual dielectric testing is completed at the same time as the annual inspection.

While user manuals identify the items to be inspected, it takes someone with the proper training, knowledge and experience to ensure a thorough inspection is completed. Often, an aerial lift or digger derrick is sent to Terex Utilities for repairs after an annual inspection has been performed by another party.  In many instances, these repairs can be minimized or eliminated by ensuring a timely and thorough inspection has been completed by a qualified factory trained technician. 

According to factory trained technicians at Terex service centres, the following are some of the most frequently overlooked inspection items, listed in increasing order of seriousness. 

Missing decals

Operational and safety decals provide valuable information to the users. Power washing equipment over the course of a year takes a toll on decals. Sometimes it’s not obvious what’s missing from the equipment if you don’t know what decals are supposed to be there. In particular, it’s especially important to make sure hand signal charts aren’t missing from digger derricks. The hand signals provide a means to communicate between the operator and ground personnel when they are in a noisy environment.  

Failure to communicate clearly could lead to possible injury or equipment damage and could result in an OSHA violation.

Hydraulic oil and filters

Oil levels must be checked according to the manufacturer’s recommendations for equipment to operate as designed. 

More frequent checks, based on operating and weather conditions, may be necessary.  Low levels, if left unattended, could lead to high dollar, unplanned repairs. Burning up one pump is easily a $2,000 repair, not to mention the loss in productivity from the equipment being out of service. Checking the fill level when the outriggers are extended can often lead to over-filling. An overfilled system leaves no room for expansion which can contribute to oil leakage.

A dirty oil filter can lead to accelerated wear and damage to pumps, cylinders, hydraulic valves and hoses due to the fact the filter is no longer capturing harmful contaminants and particles circulating in the fluid.  

Damaged winch rope 

In addition to the daily visual inspection, the full length of the winch rope should be unspooled and inspected hand-over-hand during the annual inspection.  When you feel cuts, frays or any indication of internal rope damage such as flat areas, bumps, or lumps that can be caused by shock loading or kinking, the rope should be replaced. Additional inspection and replacement criteria are available from the rope manufacturers.

Rotation bearing bolts 

While the process is simple, this is one of those items that cannot be overlooked.   It may be easier to inspect and re-torque bolts with two people—one to rotate the bearing and the other to check the bolt torque.  Information on the proper bolt torque and lubricant is available in the manual and on the Terex Utilities website.   Failure to maintain proper torque could lead to bearing bolt failure due to overloading the remaining fasteners.  It can also lead to bearing failure representing a $6,000 to $10,000 repair. 

Bearing backlash

Checking the amount of allowable play in the rotation bearing takes time and a proper understanding of how to measure it. If there is too much play, this may be an indication that the rotation bearing could be worn and needs replacement.  In addition, it could also be an indication the boom has been shock loaded.  

Levelling chain 

Levelling systems on aerial devices should have specific amounts of preload.  Too much or too little tension increases wear and possible damage.  Checking levelling tension requires taking the boom cover off. Failure to keep the chain within tolerance could affect the self-levelling of the bucket as the boom moves through the range of motion.

Bucket and liner damage

Cracks, gouges and damage to the aerial device bucket could affect its structural integrity.  As well, cracks, gouges and wear on the liner contribute to reducing dielectric strength. Often, we find inspectors fail to remove the liner when looking at the bucket. Tools are often dropped, which damage the liner and the bucket itself, so look underneath, inside and out of the bucket.


While conducting your own annual inspections may seem the most affordable option, be sure to consider whether your technicians have the expertise required for the specific equipment. The same is true if you choose to outsource the inspection. If you are hiring someone else to do the inspection for you, make sure you choose a company that has qualified and trained technicians for the type of equipment being inspected. 

It’s the owner’s and user’s responsibility to have qualified personnel perform the inspections. To properly conduct the inspections, the technician should be a qualified person who possesses an appropriate technical degree, certificate, professional standing or skill, and who by knowledge, training and experience has demonstrated the ability to deal with problems relating to the subject matter work or project.

For those owners who perform annual inspections in-house, Terex offers several training programs designed to provide technicians with the knowledge to become a qualified inspector to conduct annual inspections. 

There are a number of benefits to using the manufacturer’s inspection services.