A319
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Confusion
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Clearance
Human Factors
I was the pilot monitoring and Check Airman for the BRAVS RNAV departure from Atlanta.  We were cleared to line up and wait on Runway 27R.  Our takeoff clearance was changed to:  At the middle marker; turn to heading 250 degrees and climb to 10;000 feet.  I immediately started looking for an indication of the marker beacon on this Airbus 319 to no avail.  We knew we had gone too far when tower asked us what our heading was and if we were receiving the marker beacon.  We immediately turned to 250 degrees and we got handed off to departure control.  As far as we could tell; there was no other aircraft near us vertically or horizontally.I should know how to identify the middle marker first and foremost.  Upon reflection; I believe the clearance is a pretty good set up because tower gave us no time to think through a takeoff clearance that changed from our clearance...and he gave it to us on the cleared for takeoff verbiage.  Next time I will deny the takeoff clearance until I can be sure to follow it.
A319 Captain reported a track deviation on takeoff from ATL when; just prior to takeoff; they received a last minute change to their clearance that involved a turn at the middle marker. Reporter indicated he could not locate the middle marker.