Date: 201307
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Light: Daylight
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: FMS/FMC
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Human factors: Communication Breakdown; Distraction; Situational Awareness; Workload; Confusion
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight; Pre-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action; Flight Crew Returned To Clearance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Human Factors; Aircraft; Company Policy
Primary problem: Aircraft

Narrative: Both FMS were MELed. We had no ACARS; RNAV; etc. Both Captain and I recognized the increased threat level due to this MEL. A thorough briefing was done on our routing. During this period; we queried ATC that allowed for a simpler routing given the navigation limitations. The flight plan that Dispatch gave was no different than for any other routine flight. Problem was we had to make a turn off of a waypoint and then go direct to a low VOR that was over 180 NM away. We realized that there was a good chance that we would not be able to get a good signal from that far away. The aircraft was taxiing out as we made our request. The Controller working Data said he did not have a chart in front of him. He said he would talk to Center and then Approach to see what he could do. He came back saying Center and Approach don't quite understand what you need. He asked if we could give a requested route. Both we and the Controller agreed to a reroute that would cut down on the complication somewhat. We briefed that new routing and then departed.While talking to Departure; that Controller queried us on our navigation capability. We told him /A and that we are not RNAV capable. He said he was sorry to be nit-picky but I'm gonna have to re-clear you. He gave a slightly different route that had us go direct to the same VOR that we were afraid we wouldn't pick up that far. We read it back and started planning. The aircraft was nearing the first VOR fix that we were to cross over. We both knew we had to fly over a specific outbound radial for about 20 NM. After that was a waypoint and then only 3 NM after that was another waypoint from which we had to turn to that rerouted VOR. I as pilot not flying looked down to grab the enroute chart and started tuning in another VOR on my side to get a cross radial for the waypoint. As a look up at Captain's PFD; we are at approximately 3 NM from the first VOR and then starting a major left turn away from the radial. ATC then begins asking about where we are going and the confirm heading. I tell ATC; back to the 060; for the outbound. The Controller says very good. Captain says that's not right but begins the turn back there. I then tell him to look at the DME and then he realized his error. He turned at the 3 NM DME mark because he had in his head that we had to turn 3 NM after the waypoint. Captain tells ATC he would just like as much radar vectors as possible. ATC gives a heading and to proceed direct to the VOR when able. Threats were the MEL'ed FMSs. Another is the lack of practice utilizing conventional navigation. Error was fixating on DME and losing the situational awareness of what the number meant. The undesired state was the lateral deviation. Make it clearer that refusing an aircraft for this MEL will not result in any discipline.




Synopsis: An EMB-145 departed with both FMC's inoperative and had difficulty navigating on airways defined by LVOR's and airway intersections needing radial and DME information for description.