Canon IR1600 Reference Manual page 50

When feeding large-size paper, pull out the auxiliary tray.
1
3
Press
the control panel.
4
Load the paper in the stack bypass with the side to be printed on facing down.
Make sure that the height of the paper stack does not exceed the limit mark.
Align the required number of sheets of paper with the slide guides. Insert the paper into the machine until
it stops.
STACK BYPASS SIZE
1-32 Making Prints Using the Stack Bypass
Auxiliary tray
(Paper Select) repeatedly until the indicator for the stack bypass lights up on
A3