MD-80 Series (DC-9-80) Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 200; Flight Crew Total 20000; Flight Crew Type 12000
Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors; Environment - Non Weather Related
We were about 3 hours into our flight when the deviation occurred. Earlier in the flight we were encountering Mountain Wave and various levels of Turbulence over the Rockies and west of the Rockies.  We were given a Direct to BAM which we proceeded to fly.Sometime later we were given a Direct to SLOWN intersection; then Direct to BAM; on course.After a Frequency change; or two; we were informed by Salt Lake Center that GPS jamming was now in effect for our area.  We noticed shortly thereafter that our navigation was no longer a GPS; but now dead reckoning.  We already had the next VOR (BAM) in our radios; so we made sure we had a good identifier and proceeded direct to BAM.We forgot that our earlier clearance of direct BAM was superseded by the Direct SLOWN clearance.  We were in the middle of taking bathroom breaks when ATC advised us of being off-course.  The First Officer (FO) was flying at the time and flew the vector assigned. When I came back into the cockpit; the FO went back to use the restroom.  We were cleared back to BAM; we were fairly close to BAM at the time; with very strong winds out of the North our turn was going to overshoot our desired course; the controller gave us a heading direct to 'LLC when able'Losing our GPS function in the aircraft is not much of a problem; except when we are specifically flying direct to a fix.  Some of our airplanes have IRU's which is then no problem.  On this airplane; when it happens again; we should recheck our Situational Awareness; ask for vectors until we are assured of what course of action we will take.
Air carrier Captain is informed of GPS jamming in ZLC airspace and issued a revised route of direct SLOWN direct BAM. When the jamming takes effect; the crew forgets they were cleared direct SLOWN and uses the VOR to proceed direct BAM; which ZLC questions.