High Speed Aileron – is a term called for the movement of Spoiler.
The Spoilers are located at inboard side of the wings. At high speeds the Spoilers move to assist the Ailerons movement to roll the Aircraft in the required direction.
In normal conditions to roll the Aircraft left, the left Aileron goes up and the right Aileron goes down, at a pre-determined speed to roll the Aircraft left, the left Spoiler goes up deflecting into the free air stream along with the ailerons.
Air Brakes / Speed brakes – is when the Spoilers are used to dump the excessive speed and increase the Rate of Descent, it is usually done in an event of Emergency, like- Cabin Pressurization failure etc.
The operation of the Spoilers vary from the Aircraft types and are usually restricted from usage below a specified height, which varies from the Aircraft models, but is usually restricted below 3000 feet, because it increases Drag tremendously and cause a significant increase in Rate of Descent.
Lift Dumpers – is when the Spoilers are used on ground after landing to dump the Lift and exert positive pressure of weight on wheels. They are automatically deployed on ground after landing, when the sensors located on the wheels assembly senses that the Aircraft has touched down by sensing the weight on wheels, both Spoilers come up and dump the excessive Lift by opening above the wing.
They reduce the landing roll and are very useful, therefore it is a normal practice followed by the Airlines to deploy the Spoilers along with using Thrust Reversers.