False engine fire warning caused return land.

Attributes
ACN	284635
Time
Date	199410
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : mia
State Reference	FL
Altitude	msl bound lower : 1500 msl bound upper : 2000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : mia tracon : pns
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 180 flight time total : 3100 flight time type : 500
ASRS Report	284635
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical inflight encounter : weather other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa other other : unspecified
Resolutory Action	flight crew : declared emergency none taken : unable other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

Shortly after contacting miami departure, the left engine fire warning system activated. We discharged both halon fire extinguishing bottles into the engine nacelle as per the emergency checklist procedures. The fire warning persisted. We then advised ATC of our emergency situation and were given immediate clearance to return to miami to land. We were not advised if we received landing priority over any other traffic. After landing, we were met by several fire/rescue vehicles and they immediately advised us there was no visible sign of fire. We continued to our ramp. Mechanics later told us the fault was with the fire warning loop wire which developed an exposed section near the engine exhaust, which, when combined with airframe vibration and heavy rain and moisture during takeoff, was the most likely cause of the false fire warning. At the time, however, we had no way of determining this in flight. The situation was treated as per the emergency procedures.

Original NASA ASRS Text

Title: FALSE ENG FIRE WARNING CAUSED RETURN LAND.

Narrative: SHORTLY AFTER CONTACTING MIAMI DEP, THE L ENG FIRE WARNING SYS ACTIVATED. WE DISCHARGED BOTH HALON FIRE EXTINGUISHING BOTTLES INTO THE ENG NACELLE AS PER THE EMER CHKLIST PROCS. THE FIRE WARNING PERSISTED. WE THEN ADVISED ATC OF OUR EMER SIT AND WERE GIVEN IMMEDIATE CLRNC TO RETURN TO MIAMI TO LAND. WE WERE NOT ADVISED IF WE RECEIVED LNDG PRIORITY OVER ANY OTHER TFC. AFTER LNDG, WE WERE MET BY SEVERAL FIRE/RESCUE VEHICLES AND THEY IMMEDIATELY ADVISED US THERE WAS NO VISIBLE SIGN OF FIRE. WE CONTINUED TO OUR RAMP. MECHS LATER TOLD US THE FAULT WAS WITH THE FIRE WARNING LOOP WIRE WHICH DEVELOPED AN EXPOSED SECTION NEAR THE ENG EXHAUST, WHICH, WHEN COMBINED WITH AIRFRAME VIBRATION AND HVY RAIN AND MOISTURE DURING TKOF, WAS THE MOST LIKELY CAUSE OF THE FALSE FIRE WARNING. AT THE TIME, HOWEVER, WE HAD NO WAY OF DETERMINING THIS IN FLT. THE SIT WAS TREATED AS PER THE EMER PROCS.

Data retrieved from NASA's ASRS site as of July 2007 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.