Glossary of Aerial Lift Equipment Terms

A glossary of aerial lift, mobile elevated work platform (MEWP), boom lift, scissor lift, rough terrain, safety, and equipment terminology.

Anti-re-start system
A safety interlock on self-propelled mobile elevated work platforms (MEWPs) that requires the operator to cycle the key or ignition switch off and then back on before the engine or motor can be restarted, preventing accidental starts.
Active oscillation system (AOS)
A term used by manufacturers like JLG or Genie for the system that automatically locks the oscillating axle when the boom is raised above a specified height or when required by the control system, ensuring stable operation on rough terrain (RT).
Auto leveling
A system, typically found on outrigger- or stabilizer-equipped lifts, that automatically positions the chassis or base frame to a level position after deployment, usually within a tolerance of 1.5 degree or less, ensuring safe operation.
Auxiliary functions
Functions on the platform control panel that operate without requiring the main lift or drive power. This often refers to auxiliary power functions like lowering the platform slowly in the event of main power loss. For a telehandler forklift, the auxiliary functions refer to the secondary hydraulic capabilities that power various attachments beyond standard forks, providing the machine with immense versatility on job sites.
Auxiliary power
A secondary power source (e.g., a small electric motor and pump) used to operate limited functions, such as gravity or slow-descent lowering, in case of a primary engine or main power failure.
Construction model
An aerial lift designed and configured specifically for harsh, rough terrain (RT) environments typical of job sites, often featuring oscillating axles, high ground clearance, and durable components.
Contact pressure
The pressure, measured in pounds per square inch (PSI) or kilopascals (kPa), exerted by the weight of a machine on the surface it rests on, crucial for understanding required ground support, especially with outrigger feet.
Drive and set
A common operational feature, particularly in towable boom lifts, where the unit can be driven short distances to a new location while the outriggers are partially deployed, or "set" to a driving configuration.
Drive enable
A safety switch or button that must be held or pressed to allow the machine's drive functions to be engaged. It prevents accidental movement and ensures the operator is in a safe driving posture.
Drive hubs
The assemblies, typically planetary reduction gears, located at the wheel positions that transmit power from the drivetrain to the wheels, allowing the machine to propel itself.
Dynamic brake
A braking action that occurs automatically when the drive or steer control is returned to neutral. It uses the drive system's motor/pump resistance to decelerate the machine quickly and smoothly.
Emergency descent
A feature, powered by the auxiliary power system, that allows the platform to be lowered slowly to the ground in the event of main power failure or engine malfunction. This is typically activated from the ground control panel.
Emergency stop
A readily accessible, red mushroom-head button on both the platform and ground control panels that, when pressed, immediately cuts all power to hydraulic and electrical functions, overriding all other controls.
Extend/retract
The action of increasing or decreasing the length of the telescopic boom sections (telescopic booms) or the extendable axles (chassis).
Extendable axles
Axle assemblies that can be hydraulically extended outward from the chassis body to widen the machine's stance, increasing stability, particularly at height.
Fall arrest/restraint
The requirement for the operator to wear a full-body harness and lanyard attached to an approved anchor point in the platform. Fall arrest stops a fall; fall restraint prevents the worker from reaching a position where a fall could occur.
Four-wheel drive
A machine where all four wheels receive engine power, providing maximum traction and gradeability for Rough Terrain (RT) applications.
Function enable switch
A momentary or maintained switch required to be active for specific hydraulic functions (like boom movement or drive) to operate, serving as a secondary safety interlock.
Function test
A check performed during the pre-operation inspection to ensure all machine controls and safety devices (e.g., limit switches, level/tilt alarm, brakes) are working correctly according to the manufacturer's specifications.
Grade
The measure of a slope's steepness, typically expressed as a percentage. A 45 degree slope is a 100% grade.
Gradeability
The maximum percentage grade or slope a self-propelled aerial lift is capable of ascending or descending safely, typically determined by drive power and stability.
Ground control panel
The operator interface located on the machine's chassis or base, used to control the machine's core functions (e.g., engine start/stop, lift/lower) from the ground for maintenance, setup, or emergency rescue.
Horn
A signaling device, typically button-activated from the platform control panel, used to alert personnel in the work area of machine movement or to signal distress.
Hydraulic cylinders
Linear actuators that use pressurized hydraulic fluid to convert hydraulic power into mechanical force, enabling the extend/retract (telescoping) and up/down (lifting) movements of the boom sections and operation of outriggers.
Industrial model
An aerial lift designed for smooth, flat, indoor surfaces, characterized by non-marking tires, smaller chassis, and often an electric-only power source.
Jib boom functions
The hydraulic movements (e.g., up/down, swing) of the jib boom—a short, hinged extension at the end of the main boom—which provides extra range and flexibility for precise platform positioning.
Level/tilt alarm
An audible and visual warning device that activates when the machine base or chassis exceeds the manufacturer's specified maximum allowable angle of inclination, indicating an unsafe condition for elevation.
Load holding system (LHS)
Hydraulic valves (often check or counterbalance valves) built into the lift cylinders that mechanically lock the cylinder in place and prevent the boom from drifting or dropping, even in the event of a hose burst or pressure loss. This is a critical safety component.
Limit switch
An electro-mechanical device that physically detects the presence or absence of an object or the end of a range of motion (e.g., a boom section fully retracted) and sends an electrical signal to the control system to stop or change a function.
Load-sensing system (LSS)
An electronic safety feature that continuously monitors the combined weight of the operator, tools, and materials in the platform. If the calculated weight exceeds the unrestricted or restricted platform capacity, the system prevents further movement of the boom or drive functions.
Manually operated
An aerial device, such as a manually-pushed work platform, that relies entirely on human physical effort for propulsion and positioning. Also referred to as "manually propelled."
Narrow (N)
A configuration of a machine's chassis that is reduced in width to allow access through confined spaces such as standard doorways or narrow industrial aisles.
Ninety-degree steering
A steering system, often found on scissor lifts and some smaller boom lifts, that allows the drive wheels to turn 90º, enabling the machine to pivot within its own footprint.
Occupied floor pressure
The pressure exerted on a supporting structure (e.g., a commercial floor or bridge) by a machine, including the weight of the platform occupants and materials. See contact pressure.
Oscillating axle
An axle assembly, typically on rough terrain (RT) lifts, that pivots vertically to keep all drive wheels in continuous contact with uneven ground, enhancing traction and stability.
Outriggers
Hydraulic cylinders with supporting pads (feet) that are extended downward and outward from the chassis to provide a solid, stable base for high-reach operation, taking the machine's weight off the tires.
Parking brake
A mechanical or dynamic braking system that automatically engages when the drive controls are in neutral or the machine is powered off, preventing unintentional movement.
Platform control panel
The operator interface located within the work platform basket, used for all primary driving and boom functions during operation.
Platform height
The vertical distance from the ground or base surface to the floor of the work platform when it is fully extended. This value is typically 6 feet less than the working height.
Platform level and platform rotate
Platform level refers to the system (often hydraulic) that keeps the platform floor horizontal throughout the boom's range of motion. Platform rotate refers to the function that allows the platform basket to be rotated horizontally relative to the boom end.
Pothole guards
Spring-loaded or mechanically deployed steel plates/bars mounted beneath the chassis of most scissor lifts that automatically drop down to prevent tipping if a drive wheel unexpectedly enters a deep hole or depression.
Pre-delivery inspection (PDI)
A comprehensive inspection and testing procedure conducted by the dealer/supplier before a new or serviced machine is delivered to the customer, ensuring it meets all operational and safety standards.
Pre-operation inspection
A mandatory visual inspection and functional test performed by the operator before each shift or use to verify the machine's condition, functionality, and safety systems.
Proportional controls
A control system that allows the operator to vary the speed of functions (drive, lift, steer) smoothly and incrementally based on the displacement of the joystick or control lever. These are essential for precise telescopic and articulating boom lifts.
Proportional-drive joystick
A control lever that allows the operator to regulate the speed of the drive motors (or hydraulic functions) based on how far the joystick is pushed from the neutral position, enabling smooth, incremental movement.
Range of motion
The total geometric area (the working envelope) that the platform can reach, including maximum working height, maximum horizontal reach, and the space between these points.
Restricted platform capacity
The maximum allowable platform load (personnel and tools/materials) that can be lifted only when the boom is positioned within a specific, limited working envelope (e.g., less reach, specific angle). This capacity is lower than the unrestricted platform capacity.
Rough terrain (RT)
A designation for machines designed to operate on unpaved, uneven ground, featuring rugged tires, oscillating axles, and high ground clearance.
Self-propelled
A machine capable of driving itself across a worksite without assistance, with controls operated from the platform.
Slewing ring (Turntable bearing)
The large-diameter bearing assembly that connects the rotating turntable (upper structure) to the non-rotating chassis (lower structure) of a boom lift, allowing for smooth, continuous turntable rotate movement.
Stabilizers
Support devices, similar to outriggers but typically less robust, that extend vertically or horizontally to aid stability and often require a solid surface for deployment.
Steer control thumb rocker
A small, two-position switch, usually located on the proportional-drive joystick, used to control the direction of the steering wheels (left or right).
Tailswing
The distance the rear section of the rotating turntable or chassis extends outside the width of the non-rotating base frame during rotation. Zero or minimal tailswing is critical in confined spaces.
Terrainability
The machine's ability to safely and effectively traverse varied and challenging ground conditions, a factor of gradeability, traction, and ground clearance.
Tracked-drive (Spider lift)
A specialized category of self-propelled mobile elevated work platform (MEWP) that utilizes rubber tracks instead of wheels for superior terrainability and low contact pressure, often referred to as a spider lift. Popular for indoor use and sensitive outdoor landscaping/arbor work.
Turning radius
The smallest circular path a machine can follow when turning the steering wheels to their maximum angle. The inside turning radius is a key specification for confined work areas.
Turntable rotate
The ability of the upper structure (the turntable, boom, and platform) of an articulating or telescopic boom lift to rotate continuously or through a limited angle horizontally on the chassis base.
Two-wheel drive
A machine where power is supplied to only two of the four wheels (usually the front or rear), suitable for operating on paved, level, or Industrial surfaces.
Unrestricted platform capacity
The maximum allowable platform load (personnel and tools/materials) that can be safely lifted throughout the machine's entire range of motion or working envelope.
Up/down
The control function used to raise or lower the platform/boom assembly vertically.
Working height
The vertical distance from the ground to a height of approximately 6 feet above the platform height. This is the practical maximum height at which a worker standing in the platform can perform tasks.
Workplace inspection
A thorough evaluation of the intended work area by the operator/supervisor before lift deployment, checking for hazards such as uneven ground, overhead power lines, drop-offs, and required clearances.
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