B737-800
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Troubleshooting; Confusion; Workload
Aircraft Equipment Problem Less Severe
Flight Crew Rejected Takeoff; General Maintenance Action
Aircraft; Airport
We were cleared for takeoff on Runway 15R at BWI. I was the Pilot Flying. When we lined up on the runway the data in my [display] did not look accurate. I elected to vacate the runway. We assessed the information and were re-cleared for take off with no further issue.
Prior to pushing up the throttles up for takeoff; the Captain stated that their [display] was not correct. I told Tower we were going to taxi clear as there was an aircraft on final. We looked down and the Flight Director was not displaying guidance even though the switches were on and the FMS correctly loaded.At the gate we had some kind of electrical MEL (I can't recall what). Also the IRUs were not aligning like normal. We called Maintenance who sent contract BWI Maintenance who told us that the gates at BWI had a problem with acquiring the GPS signal (this was strange as the terminal was north of the plane so that the plane had a clear path towards the equator). We discussed and the Captain decided we would push into the alley to try and get a signal. Again that didn't work and we discussed with Maintenance on the ops frequency who told us the closer we got to the runway it would work. We decided to taxi towards the runway. On the taxi out GPS 2 acquired a signal; but was intermittent. We pulled into the de-ice area adjacent to Taxiway P by Runway 15R. Finally we got both GPS signals to acquire which was required for our RNAV route and Required RNP FMS message.If the BWI gates historically have problems with acquiring the GPS signal; then a note about that (and if associated the Flight Directors not providing guidance) should be added to the company pages in the Jeppesen FD Pro App. If the failure was associated with the MEL; then a note about it and the flight directors not providing guidance should be added to the associated MEL in the B737 NG Minimum Equipment List / Configuration Deviation List.
B737 pilot crew reported the IRU's would not align; resulting in a rejected takeoff.