AN EMB145 LANDING GEAR WOULD NOT RETRACT AFTER TKOF. ALSO; MASTER WARNING WENT OFF AND LAV SMOKE EICAS MESSAGE APPEARED. CREW DECLARED EMERGENCY AND RETURNED TO FIELD.

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FLT XXXX IN ACFT X FROM ZZZ BROUGHT ME THE SAME LAV SMOKE MESSAGE AT NEARLY THE SAME TIME DURING FLT. THIS TIME; WE HAD A GEAR PROBLEM AS WELL. THE LNDG GEAR DIDN'T WANT TO RETRACT WHEN WE TOOK OFF. WHILE I WAS TRANSMITTING TO ATC THAT WE'D BE RETURNING TO LAND IN ZZZ; THE MASTER WARNING WENT OFF WITH A LAV SMOKE EICAS. THE FLT ATTENDANT KNEW THIS DRILL WELL AFTER THE FIRST INCIDENT AS WELL AS I. THIS TIME WAS DIFFERENT. THE FIRE BELL IN THE CABIN STAYED ON FOR 3 TO 4 MINUTES AND THE FLT ATTENDANT SAID THAT SHE AND A DEADHEADING CREWMEMBER IN THE BACK SMELLED SOMETHING FUNNY; LIKE A DIRTY FURNACE OR SOMETHING HOT AND DUSTY. WE DONNED MASKS AND GOGGLES AND COMPLETED MEMORY ITEMS FOR CABIN FIRE OR SMOKE. I THEN DECLARED AN EMER WITH ATC. WE ACCOMPLISHED ALL CHKLISTS AND THE FLT ATTENDANT SAID THAT THE INDICATION WAS GONE AND SO WAS THE ODOR IN THE BACK. I DOUBLE CHKED FOR CONDITIONS JUST BEFORE STARTING THE APCH AND THEN RIGHT AFTER WE CLRED THE RWY. SHE SAID EVERYTHING WAS OK; NO SMOKE; FIRE OR ODOR AT THIS TIME. WE SEEMED TO GET THE ODOR AND INDICATIONS AT HIGH POWER SETTINGS WITH TAKEOFF AND CLB THRUST. I FELT THAT THERE WAS NO NEED TO EVACUATE AT THAT TIME SO WE RETURNED TO THE GATE AND LET THE PAX OFF THERE. FIRST THE GEAR WOULDN'T GO UP AND THEN THE FIRE ALARM; ONE RIGHT AFTER THE OTHER. WE WERE BUSY UNDER THE MASKS AND GOGGLES THAT'S FOR SURE. THIS TIME AN EMER WAS DECLARED LIKE THE OPS MANUAL SAID TO DO; AND THIS TIME IT SEEMED LIKE THE RIGHT THING TO DO SINCE THE LAV SMOKE INDICATION WAS NOT JUST MOMENTARY. I SHARED MY FIRST STORY WITH A COUPLE OTHER CHK AIRMEN AND THEY THOUGHT I'D MADE A CLEAN DECISION DURING BOTH FLTS INCLUDING THE ONE IN MY PREVIOUS FLT. I THINK I MAY TELL THEM THAT PERHAPS IT WASN'T IF I'D TAKEN THE OPS MANUAL LITERALLY. EVEN IF I HAD DECLARED AN EMER ON THE FIRST FLT; SHOULD I HAVE CANCELLED IT 20 SECONDS LATER WHEN THE ALARM CEASED? I RECOMMEND TRAINING NEW HIRES REGARDING THESE EICAS MESSAGES THAT COME ON AND GO AWAY IMMEDIATELY. IT TENDS TO LEAVE AN IMPRESSION THAT IT'S A FALSE INDICATION OR THAT THE PROBLEM HAS SIMPLY GONE AWAY.