48.7 Joining on Base
48.7.1 Joining on base leg, whilst not prohibited, is not a recommended standard procedure. CASA recommends pilots join the circuit on either the crosswind or downwind leg. However, pilots who choose to join on base leg should only do so if they:
a. have determined the wind direction and speed;
b. have determined the runway in use;
c. give way to other circuit traffic and ensure the aircraft can safely (no traffic conflict likely) join the base leg applicable to the circuit direction in use at the standard height; and
d. broadcast their intentions.
I'd also like to highlight point (d) here - 'BROADCAST THEIR INTENTIONS.' Intentions are what you are GOING to do. ie. It is expected that a broadcast of intentions to join base be made when making the first inbound call (as with intentions for straight-in approach). This call should be made at 10nm or earlier (Jepp. ATC pg 716). Jepps are another publication of the AIP. If the call of actually joining on base was the first time 'old mate' piped up he has broken both (c) and (d) and I hate to be cynical but probably doesn't give a stuff about (a) and (b) also. As with driving on the roads, sometimes it is up to the law abiding citizen to make safety decisions and corrections to allow for the stupidity of others...