An E135 flight crew returned to their departure airport when the landing gear failed to retract due to a failed landing gear air/ground switch. The anomaly was a repeat performance of a write up that had grounded the aircraft for maintenance for two days prior to this departure.

Narrative

After reviewing the AML (Aircraft Maintenance Log); the Captain and I had discovered that this was a kickoff flight; and that the aircraft was returning to service after being grounded the last two days for a LG AIR/GND FAIL message and an associated failure of the landing gear to retract.Weather at the time of the flight was MVFR with broken clouds and near freezing temperatures; so a REF ANTI-ICE ON takeoff was performed. Closeout; pushback; and taxi-out were perfectly normal. After commencing the takeoff roll; we noticed considerable nose-wheel shimmying; but nothing that we considered severe. At Vr I rotated normally; and as soon as we were airborne; a single caution chime was heard; along with the EICAS message LG AIR/GND FAIL. The Captain attempted to raise the landing gear with the 'positive rate; gear up' callout; however; the handle was stuck in the down position. The Tower called saying our gear appeared to still be in the down position passing 500 FT. The Captain then informed the Tower that we'd be returning to land and we were handed off to Departure Control. At acceleration altitude; we completed the after-takeoff checklist; with the exception of leaving the flaps at 9. I continued to fly the aircraft (autopilot engaged at 1;000 FT); and handled the radios while the Captain consulted the AOM; notified the Company and Maintenance of our return and advised the Flight Attendants and the passengers. ATC asked if we were declaring an emergency; to which we replied negative. Once our tasks were complete we setup for and briefed an ILS approach to Runway XXL. We were then vectored for and completed a visual approach and landing. Touchdown; rollout; and taxi in were normal. We parked; deplaned; and the Captain logged the discrepancy in the AML.