Hi Bob, a little trivia question.

Any idea what allowances the ERC route LSALT's allow for, perhaps a 10NM radius at any point along track?
For example we're flying in a grid LSALT of 5500 with a route LSALT of 2800 at 4000 feet with no GPS tracking, how far off track can we be before terrain clearance is no longer guaranteed.
Obviously we can still refer to the WAC for obstacles, but I'm curious as to know if there's any particular distance we should keep in mind as a general rule.
This was not covered in my shiny new MECIR

Hi there Flying there,

If memory serves me correct, ERC/TAC routes use the same LSALT tolerances areas as published in AIP i.e., the 10.3 degrees splay out to 50nm +5 buffer or until it intersects with the splay from the opposite direction and add 1000ft or 1360ft.

To be sure, I checked the route from Ballarat (YBLT) to Bendigo (YBDG) on the Hamilton WAC and compared it to the same route on the TAC-4. The LSALT comes in just under what is published and then rounded up (by 8ft).

I did the same with the Grid LSALT. I used the highest piont from the WAC and applied the appropriate clearance.
The example I used was with the Hamilton WAC and added 1000ft to the spot height near Bendigo of 2992ft. This is on top of the 680 ft TV mast that is on top of a 2312 ft hill.

The thing to remember if comparing Grid LSALT on an ERC/TAC to a WAC is to look for highest spot in each 1 whole degree square.
I used between 144 and 145 degrees East by 36 and 37 degrees South for this example. The WAC has grids of half degrees and each half degree block has a highest spot height. Traps for young players.

Have a play with it and see what you get!

Cheers Mister W.