Narrative:

During landing phase for atl, approximately 20 mi out, selected APU switch to 'on' position. Initially set up to land on runway 26R in night VMC. Prior to APU attaining proper operating speed, APU fire warning light, bell, and master caution illuminated. Silenced the bell, called for APU fire checklist, and declared an emergency. Requested fire trucks to be standing by. While checklist was being accomplished, atl approach offered runway 26L to expedite our arrival. We accepted and first officer reaccomplish approach checklist for new runway. Jumpseating pilot, at my request, contacted #1 flight attendant to inquire if they smelled anything unusual. They said they smelled a burning smell but no visible smoke. After landing, we cleared the runway and I requested that the fire crew inspect the APU/tail section of the aircraft. While inspection was under way, I contacted flight attendants on interphone to inquire one more time about conditions inside aircraft. Other than faint smell, nothing abnormal reported. Fire crew then reported no visible fire or signs of damage. Continued to taxi to gate with fire crew following us until we shut down at the gate. During taxi in, informed operations and requested maintenance meet the aircraft. Made a logbook write-up. Then went down to operations and contacted duty director informing him of the situation. Next contacted union safety officer.

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Original NASA ASRS Text

Title: B737-500 CREW HAD AN APU FIRE WARNING AFTER BEGINNING THE APU START SEQUENCE IN ATL CLASS B AIRSPACE.

Narrative: DURING LNDG PHASE FOR ATL, APPROX 20 MI OUT, SELECTED APU SWITCH TO 'ON' POS. INITIALLY SET UP TO LAND ON RWY 26R IN NIGHT VMC. PRIOR TO APU ATTAINING PROPER OPERATING SPD, APU FIRE WARNING LIGHT, BELL, AND MASTER CAUTION ILLUMINATED. SILENCED THE BELL, CALLED FOR APU FIRE CHKLIST, AND DECLARED AN EMER. REQUESTED FIRE TRUCKS TO BE STANDING BY. WHILE CHKLIST WAS BEING ACCOMPLISHED, ATL APCH OFFERED RWY 26L TO EXPEDITE OUR ARR. WE ACCEPTED AND FO REACCOMPLISH APCH CHKLIST FOR NEW RWY. JUMPSEATING PLT, AT MY REQUEST, CONTACTED #1 FLT ATTENDANT TO INQUIRE IF THEY SMELLED ANYTHING UNUSUAL. THEY SAID THEY SMELLED A BURNING SMELL BUT NO VISIBLE SMOKE. AFTER LNDG, WE CLRED THE RWY AND I REQUESTED THAT THE FIRE CREW INSPECT THE APU/TAIL SECTION OF THE ACFT. WHILE INSPECTION WAS UNDER WAY, I CONTACTED FLT ATTENDANTS ON INTERPHONE TO INQUIRE ONE MORE TIME ABOUT CONDITIONS INSIDE ACFT. OTHER THAN FAINT SMELL, NOTHING ABNORMAL RPTED. FIRE CREW THEN RPTED NO VISIBLE FIRE OR SIGNS OF DAMAGE. CONTINUED TO TAXI TO GATE WITH FIRE CREW FOLLOWING US UNTIL WE SHUT DOWN AT THE GATE. DURING TAXI IN, INFORMED OPS AND REQUESTED MAINT MEET THE ACFT. MADE A LOGBOOK WRITE-UP. THEN WENT DOWN TO OPS AND CONTACTED DUTY DIRECTOR INFORMING HIM OF THE SIT. NEXT CONTACTED UNION SAFETY OFFICER.

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.