Instructor pilot, with student pilot, declared an emergency to the tower controller when smoke came ...

Attributes
ACN	422153
Time
Date	199812
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : prc
State Reference	AZ
Altitude	msl bound lower : 6000 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : lax
Operator	general aviation : instructional
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	cruise other descent other landing other
Flight Plan	None
Person 1
Affiliation	Other
Function	flight crew : single pilot instruction : instructor
Qualification	pilot : commercial pilot : cfi
Experience	flight time last 90 days : 90 flight time total : 520 flight time type : 300
ASRS Report	422153
Person 2
Affiliation	Other
Function	flight crew : single pilot instruction : trainee
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency other other
Consequence	Other

Narrative:

On a cross country training flight, we proceeded VFR from prc to sdl. Sdl underlies the phx class B airspace and is within 30 NM. We descended below the class B and contacted sdl tower. Proceeded to sdl and made a touch-and-go and departed to the northwest. In cruise flight, I contacted ZAB for VFR flight following. The center controller advised that he was getting no transponder at all, and we cycled the transponder several times with no results. I believe we were within the 30 NM mode C veil and at an underlying airport with an inoperative transponder. There were no reports of any transponder malfunctions in this aircraft in the near past. Upon entering right downwind for runway 3R at prc, I noticed a small amount of smoke coming from under the panel. I alerted my student, and the smoke became thicker. I then told tower that we had smoke in the cockpit and were going lost communication. I shut down the electrical system, the smoke stopped. So, I turned on the master switch and 1 radio. I reported back with tower, saying the smoke had stopped. They informed us that we were #1 cleared to land and that the emergency equipment was responding. We landed without incident and were escorted to the ramp by arff personnel. Maintenance found the transponder was responsible for the smoke and it was replaced.

Original NASA ASRS Text

Title: INSTRUCTOR PLT, WITH STUDENT PLT, DECLARED AN EMER TO THE TWR CTLR WHEN SMOKE CAME FROM THE INST PANEL DURING THE DOWNWIND LEG FOR LNDG. POSTFLT INSPECTION BY MAINT FOUND A FAULTY XPONDER.

Narrative: ON A XCOUNTRY TRAINING FLT, WE PROCEEDED VFR FROM PRC TO SDL. SDL UNDERLIES THE PHX CLASS B AIRSPACE AND IS WITHIN 30 NM. WE DSNDED BELOW THE CLASS B AND CONTACTED SDL TWR. PROCEEDED TO SDL AND MADE A TOUCH-AND-GO AND DEPARTED TO THE NW. IN CRUISE FLT, I CONTACTED ZAB FOR VFR FLT FOLLOWING. THE CTR CTLR ADVISED THAT HE WAS GETTING NO XPONDER AT ALL, AND WE CYCLED THE XPONDER SEVERAL TIMES WITH NO RESULTS. I BELIEVE WE WERE WITHIN THE 30 NM MODE C VEIL AND AT AN UNDERLYING ARPT WITH AN INOP XPONDER. THERE WERE NO RPTS OF ANY XPONDER MALFUNCTIONS IN THIS ACFT IN THE NEAR PAST. UPON ENTERING R DOWNWIND FOR RWY 3R AT PRC, I NOTICED A SMALL AMOUNT OF SMOKE COMING FROM UNDER THE PANEL. I ALERTED MY STUDENT, AND THE SMOKE BECAME THICKER. I THEN TOLD TWR THAT WE HAD SMOKE IN THE COCKPIT AND WERE GOING LOST COM. I SHUT DOWN THE ELECTRICAL SYS, THE SMOKE STOPPED. SO, I TURNED ON THE MASTER SWITCH AND 1 RADIO. I RPTED BACK WITH TWR, SAYING THE SMOKE HAD STOPPED. THEY INFORMED US THAT WE WERE #1 CLRED TO LAND AND THAT THE EMER EQUIP WAS RESPONDING. WE LANDED WITHOUT INCIDENT AND WERE ESCORTED TO THE RAMP BY ARFF PERSONNEL. MAINT FOUND THE XPONDER WAS RESPONSIBLE FOR THE SMOKE AND IT WAS REPLACED.

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.

Instructor pilot, with student pilot, declared an emergency to the tower controller when smoke came from the instrument panel during the downwind leg for landing. Postflt inspection by maintenance found a faulty transponder.