Flight Crew Air Transport Pilot (ATP)
Training / Qualification; Human-Machine Interface
Aircraft Equipment Problem Less Severe
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport
Human Factors; Aircraft
I was informed of an airplane swap just after I had gotten the flight plan and release. The rest of the flight crew had to gather their things switch terminals A to C. We were now hurried to get out on schedule. I get to the airplane and maintenance is on board finishing the de-fueling procedure. I get in the cockpit to review several MEL items. The right A/C pack; both FMS units; GPWS; and a fueling valve are deferred. The flight is boarded and we do the normal before start checklist. I check to make sure the headings are matched up and the IRS switch is in ATT mode. The First Officer tells me that due to the FMS units being out; we used ATT mode to get a display on attitude and heading indicators. I agreed that we were not using the IRS's anyway and it made sense. We pushed out; taxied and started takeoff roll normally. Just before 80 KTS First Officer notices the heading indicators are not correct (215 instead of 176). I decided to continue with the takeoff and just visually turned to an approximate heading. Once airborne; I quickly realized that slewing the heading indicators was not an easy task. We requested a return to the airport and I visually flew the aircraft around the pattern and landed. We returned to the gate without any problem. I believe I missed the heading check when taking position on the runway because we needed to turn off the operating pack per MEL. I also thought we could correct the headings once airborne. There is no MEL FMS out guidance and we did not get any malfunction warnings to lead us to the QRH.
MD83 Captain reports being dispatched with both FMS units inoperative and discovers during the before start checklist that the IRS's have been aligned in the ATT mode; which seemed reasonable. During takeoff heading errors are discovered but the Captain elects to continue. Once airborne; correcting the heading errors is found to be difficult and the flight returns to the departure airport.