Date: 201501
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Toilet Smoke; Overheat; Fire Detectors & Warning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew; Person Flight Attendant
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We were on the RNAV arrival WX was CATI; multiple speed requests; final one was to maintain 170K until FAF; planning on flaps 30; auto brake 1; First Officer (F/O) was flying the aircraft; and I was the PM/PNF (pilot monitoring/pilot not flying). This happened very-very quickly. Our position was just prior to the FAF when the event happened; maybe 4 minutes to touch down; then maybe 5 minutes to the gate. We had a hard time afterwards putting the sequence of events together since it was so fast time wise. We were just outside FAF; maybe 8 miles on the approach; had flaps 5 extended; F/O asked for the gear down; complied and armed the speed brake. Shortly afterwards; we both heard a noise; we look at each other; the F/O asked what the noise was; and I said I did not know but it sounded like maybe a door seal leak in back. Got the chime call from the back. I turned up the service interphone knob; said hello; and when the Flight Attendant (F/A) answered I got blasted by a high pitch alarm (F/O instantly turned his off as it was really overpowering). The A F/A told me; having to yell to get above the alarm; that the aft lavatory alarm was going off. I asked her if there was any smoke or fire in the lavatory; she looked into the lavatory and said no. I told her that we will be landing immediately then and she informed the others and returned to her seat. At the same time we got the call from the back; Final App told us to contact tower. Since I was on the interphone with the F/A's; the F/O asked them to standby as we had a problem in the back. After I finished with the F/A's; I got back with the copilot; knew that Final tried to pass us to Tower. I did that; Tower told us we were cleared to land. I then came back to Tower and let them know about the lavatory alarm and that we were going to continue the landing. I asked for the fire trucks to follow us and that we most likely would go to the gate (we had just an alarm; not smoke or fire). He asked another question about the issue; I remember responding but do not remember what was said. We continued to configure and ran the landing checklist. I think the Tower asked us if we wanted to declare an emergency; the F/O confirmed that he would; and I believe I said yes (thank you to whoever it was in the tower that backed us up on declaring an emergency); but neither one of us is sure because we got interrupted with a caution light; looked up and saw that we had an 'equipment cooling exhaust light' (the cooling off) on. We continued with the plan to land. The landing was quite normal except for a pressurization 'bump' that everyone felt in their ears; and another caution light. We looked up and saw that the 'auto fail' light was now on. On landing roll; Tower asked us again if we were declaring an emergency. I said yes; and that we needed to get to the gate to get the fire department on the aircraft to check things out. We transferred controls and exited [the runway].  As we got onto [taxiway]; I looked over towards the fire station and saw that the fire trucks were just exiting their bays; and tower cleared us to cross the center runway. I asked the F/O to contact the F/A's in the back to find out if there was any smoke or fire yet. They said no and informed us they had the fire extinguishers and PBE out and available. Since that was the 2nd confirmation of no smoke or fire and the fire trucks were just approaching the terminal; I decide against stopping and doing an evacuation on the taxiway. As we were crossing the center; tower cleared us across the left runway. As I turned north; the first fire truck heading south passed abeam us. The fire department reported no signs of smoke or fire. This was confirmation #3 that there was no fire; so I elected to continue to the gate. The F/O contacted company and ramp to let them know; and started the APU. I had the F/O tell the F/A's that we were headed to the gate and that I wanted all of passenger's to get off the aircraft in an expedited manner and to leave all of their belongings behind. We got to the gate; ramp was not ready for us (looking for a set of wands) and I kept inching towards the gate. The ramp lead then started noticing all of the fire trucks pulling in behind us and started yelling at his crew. The wands quickly appeared; power was quickly applied; and we shut down the engines and APU; performed the shutdown checklist. I jumped up and opened the door. The controlled evacuation was proceeding in a nice calm manner (no panic and the F/A's doing a great job) but slow (four wheelchairs); several fire department personnel were already in the jet way and ready to get on the aircraft after everyone was out. I also noted at this time that the forward lavatory alarm was activated too. The fire department boarded; found nothing; we reset the alarms. Maintenance (MX) came on; found nothing either. I filled out the MX log book; briefed everyone; made calls to dispatch and the duty officer; then the F/O and I proceeded to our next flight. A series of aircraft malfunctions:Aft & Fwd lavatory smoke alarms going off with no smokeEquipment exhaust cooling light came onAuto Fail light came on




Synopsis: B737 Captain is in formed during approach by the Flight Attendants that both lavatory smoke alarms are going off but no smoke was seen. The approach is continued and just before landing the Equipment exhaust cooling light and the Auto Fail light came on. the aircraft continues to the gate with ARFF following but no smoke is ever seen.