Narrative:

Assigned to operate [a] ferry flight from ZZZ to phl. The aircraft being ferried [requested priority handling with ATC] the day prior and returned to ZZZ after takeoff. After takeoff; a smell of an electrical burn and lav smoke master warning [was] encountered. Returned to ZZZ.after takeoff; around 200 feet; both the captain and I noticed the smell of an electrical burn. Passing through 400 feet the aircraft produced a lav smoke master warning. No other warnings; cautions; or advisories were present. Cause unknown. MEL was signed off from the day prior by maintenance in the logbook.once the aircraft was cleaned up; we ran the lav smoke QRH procedure. Once that was complete I ran normal checklist; sent an ACARS message; and set up for the approach while the captain flew the aircraft and handled ATC. We wanted an immediate return to ZZZ and vectors to final for the lda runway xx.no suggestions at this time. Since the captain was flying it was easy for him to take control of the radios while I ran the checklists. It is my belief that in any emergency situation; no matter who is the pilot flying; the cockpit should be divided such that the captain is the one communicating with ATC throughout most of the emergency. That way the captain doesn't have to listen to an ATC request; make an informed decision; tell his first officer what to say; and then [pass it] off to ATC or the flight attendant. I am reviewing our publications currently to see if this is SOP.

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Original NASA ASRS Text

Title: EMB-145 First Officer reported smelling an electrical burn and receiving a LAV SMOKE master warning after takeoff.

Narrative: Assigned to operate [a] ferry flight from ZZZ to PHL. The aircraft being ferried [requested priority handling with ATC] the day prior and returned to ZZZ after takeoff. After takeoff; a smell of an electrical burn and LAV SMOKE master warning [was] encountered. Returned to ZZZ.After takeoff; around 200 feet; both the Captain and I noticed the smell of an electrical burn. Passing through 400 feet the aircraft produced a LAV SMOKE master warning. No other warnings; cautions; or advisories were present. Cause unknown. MEL was signed off from the day prior by Maintenance in the logbook.Once the aircraft was cleaned up; we ran the LAV SMOKE QRH procedure. Once that was complete I ran normal checklist; sent an ACARS message; and set up for the approach while the Captain flew the aircraft and handled ATC. We wanted an immediate return to ZZZ and vectors to final for the LDA Runway XX.No suggestions at this time. Since the Captain was flying it was easy for him to take control of the radios while I ran the checklists. It is my belief that in any emergency situation; no matter who is the Pilot Flying; the cockpit should be divided such that the Captain is the one communicating with ATC throughout most of the emergency. That way the Captain doesn't have to listen to an ATC request; make an informed decision; tell his First Officer what to say; and then [pass it] off to ATC or the Flight Attendant. I am reviewing our publications currently to see if this is SOP.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.