Flight crew reported that; on aircraft power up; the forward lavatory fire alarm began to sound and ...

Narrative:

I arrived to the gate along with one other flight attendant. The airplane had been moved [to this gate from another] with little notice so everyone was making their way to the jet. When we got onboard; the jet was far too hot to allow passengers on; so I ran up and told [customer service] to hold off on boarding until the ca (captain) told her it was ok and ran back to start the APU. The aircraft was in the terminate checklist configuration so I closed the east. Exit light switch and battery switch and started the APU. Once I placed the APU generator on the busses; I got a loud alarm that sounded like an ee overheat alarm. I quickly shut off the INS and checked all of the fans running and in normal. The alarm did not abate. I took the APU off line and put the plane on ground power. The alarm continued. I disconnected ground power and turned the battery switch off and ee lights switch off; essentially returning the aircraft to the terminate configuration. This was the only configuration that made the alarm stop. By this time the captain was onboard; along with the rest of the flight attendants. The captain entered [a digital maintenance] report and verbally notified maintenance. On the radio; maintenance asked if the alarm was coming from the floor and we said it was hard to tell but it sounded like an equipment cooling alarm. We did try placing the aircraft on the ground service bus; but that didn't change the alarm status. As long as it was on gp or APU; the alarm continued. I went outside to do the walk around and did not notice the alarm outside which I reported when I returned. By this time the first maintainer came onboard and began troubleshooting. He did all of the same things I did; and was unsuccessful. After 10 minutes; he called for backup. During this time; the flight attendants; the pilots and the maintainer were all onboard listening to the constant alarm with nobody able to identify it. Three more avionics technicians came onboard and did a sweep of the aircraft and finally figured out it was the forward lav fire alarm. Obviously there were no secondaries and nobody really knows why it got set off. It was reset and the flight continued with no further incident.

Original NASA ASRS Text

Title: Flight crew reported that; on aircraft power up; the Forward Lavatory fire alarm began to sound and was mistaken for an aircraft equipment cooling alarm; resulting in a delay.

Narrative: I arrived to the gate along with one other flight attendant. The airplane had been moved [to this gate from another] with little notice so everyone was making their way to the jet. When we got onboard; the jet was far too hot to allow passengers on; so I ran up and told [Customer Service] to hold off on boarding until the CA (Captain) told her it was ok and ran back to start the APU. The aircraft was in the terminate checklist configuration so I closed the E. Exit Light switch and Battery switch and started the APU. Once I placed the APU generator on the busses; I got a loud alarm that sounded like an EE overheat alarm. I quickly shut off the INS and checked all of the fans running and in Normal. The alarm did not abate. I took the APU off line and put the plane on Ground Power. The alarm continued. I disconnected ground power and turned the battery switch off and EE Lights switch off; essentially returning the aircraft to the terminate configuration. This was the only configuration that made the alarm stop. By this time the Captain was onboard; along with the rest of the flight attendants. The Captain entered [a digital maintenance] report and verbally notified maintenance. On the radio; maintenance asked if the alarm was coming from the floor and we said it was hard to tell but it sounded like an equipment cooling alarm. We did try placing the aircraft on the Ground Service Bus; but that didn't change the alarm status. As long as it was on GP or APU; the alarm continued. I went outside to do the walk around and did not notice the alarm outside which I reported when I returned. By this time the first maintainer came onboard and began troubleshooting. He did all of the same things I did; and was unsuccessful. After 10 minutes; he called for backup. During this time; the flight attendants; the pilots and the maintainer were all onboard listening to the constant alarm with nobody able to identify it. Three more avionics technicians came onboard and did a sweep of the aircraft and finally figured out it was the forward lav fire alarm. Obviously there were no secondaries and nobody really knows why it got set off. It was reset and the flight continued with no further incident.

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.

Attributes
ACN	1673648
Time
Date	201908
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Parked
Flight Plan	IFR
Component
Aircraft Component	Toilet Smoke Overheat Fire Detectors & Warning
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 135 Flight Crew Type 1536
Person 2
Function	Captain Pilot Flying
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 137 Flight Crew Type 231
Events
Anomaly	Aircraft Equipment Problem Less Severe Ground Event / Encounter Other / Unknown

Flight crew reported that; on aircraft power up; the forward lavatory fire alarm began to sound and was mistaken for an aircraft equipment cooling alarm; resulting in a delay.