When their FMS and associated autoflight systems malfunctioned while flying an RNAV SID the flight crew of a B737-300 requested and received vectors from Departure Control. Functionality was later restored and the flight continued to destination.

Narrative

We were departing CLT Runway 36R on a MERIL RNAV SID. The aircraft was a 737-300 series. Takeoff was normal. LNAV was engaged at 400 AGL; and it engaged normally. At 1;000 AGL; pilot flying called for climb thrust; speed 210; and engaged the autopilot. The autopilot did engage on B channel. Shortly after that; both FDs biased out of view; LNAV disengaged; and the autopilot disconnected. We tried a reset of the FD's and both autopilots; but we could not get them to immediately engage. LNAV was re-engaged successfully; but since we could not get the FDs and autopilot back right away; I advised CLT Departure that we needed a vector; and could not continue the RNAV SID. He gave us a heading of 090 degrees. The autopilot and FDs were engaged again soon after we were placed on the vector heading. Shortly after that; he asked us if we could accept direct LILIC on the MERIL RNAV SID. We preceded direct LILIC; flight plan route. The rest of the flight was uneventful with no further discrepancies noted. I could find no obvious reason for the disconnect of the FDs; LNAV; and autopilot initially. I decided that since these RNAV SIDs are closely spaced; and since we were now flying the aircraft manually; it was prudent to get an initial vector off the SID. Once the FDs and autopilot were re-engaged; we were able to go direct to a more distant fix; outside of the busy terminal environment; and not close to the airport. LNAV was monitored with no additional discrepancies noted. All other autopilot/flight director systems worked normally for the rest of the flight.I suspect this was just a spurious glitch in the flight director/autopilot system. I have flown many RNAV departures with the 737. They usually perform flawlessly.