Final answer:
The 'Q' endorsement is absent on a Class 1 licence because Class 1 drivers are assumed to have air brake knowledge, as it is part of their required training and testing for heavy commercial vehicles.
Step-by-step explanation:
The reason the 'Q' endorsement does not appear on a Class 1 licence is because Class 1 drivers are assumed to have air brake knowledge. The 'Q' endorsement is specifically related to the qualification to operate vehicles equipped with air brakes.
Since Class 1 licensing typically includes the skillset needed for operating heavy commercial vehicles, which are commonly equipped with air brakes, the training and testing for a Class 1 license already cover this knowledge. Therefore, it is not necessary to have a separate air brake endorsement displayed on the license.