MD-80 Series (DC-9-80) Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport
Aircraft
After departure at approximately 4000 MSL I heard the Lavatory Smoke Alarm going off through the closed door. Shortly thereafter the Lead FA called up and said that they had an Aft Lav Smoke Alarm on both sides. As the NFP I [advised] ATC and requested to return back to the field. Then I grabbed the EQRH (Emergency Quick Reference Handbook). The CA then confirmed that he had the plane and the radios and instructed me to run the EQRH checklist. I ran checklist for the Lavatory Smoke Alarm. After I completed the checklist I returned to my duties as NFP ran the descent/approach/landing checklist and we landed uneventfully. The CA decided to return to the gate for deplaning since the FA's could not verify a fire and an evacuation on the runway might have caused more injuries than deplaning at the gate. I agreed with that assessment. Mechanical malfunctions happen so there is not much that can be done preemptively to avoid that. What caused the Lav Smoke alarm to go off is presently unclear. The FA's and some passenger confirmed that they saw smoke/haze in the area concerned; yet an active fire could not be confirmed. Also; it did not get worse; but rather dissipated slowly. The Lav Smoke alarm remained on until we got to the gate though. I applaud the FA's for staying calm and relaying that to the passengers. As far as I know no injuries were reported. What I am a little concerned about is the EQRH checklist that deals with the Lavatory Smoke Alarm. It directs the crew to pull a lot of CB's. Those CB's are located behind the Captain's seat. I could not reach those breakers from my seat (due to phase of flight and impending landing); so the Ca had to pull them; despite him being the PF and operating the radios. For this checklist it would be better to have the controls transferred to the FO so that the CA can locate and pull the CBs without having to fly and call at the same time. In addition; the checklist directed us to pull CBs for the Call System. I do not know how that CB interacts with the Lavatory Smoke Alarm; but what it did do is disable our communication with the FA's as our call-button was rendered inop after pulling that breaker. All communication with the FA's was done by knocking and yelling through the door once [the CBs] were pulled. Though possible; it was not the best solution. But since it was part of the checklist we did not undo that step.
MD-80 First Officer reported returning to departure airport after receiving a lavatory smoke alarm.