Emergency declared when engine coughs after switching fuel tanks.

Attributes
ACN	260972
Time
Date	199401
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : fty
State Reference	GA
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : atl tower : fty tower : maf
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise other landing other other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 4 flight time total : 1044 flight time type : 500
ASRS Report	260972
Person 2
Affiliation	Other
Function	observation : passenger observation : observer
Qualification	pilot : commercial pilot : cfi pilot : instrument
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	aircraft : equipment problem dissipated controller : provided flight assist flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

En route to fty for practice ILS approachs in IMC. Had just idented fty localizer, atl VOR and flanc NDB and had just gotten fty ATIS information. Told cfii aboard I was switching from left main to left auxiliary fuel tanks. About 15 seconds after switching tanks, the engine suffered 2 momentary power interruptions. I immediately declared mayday, mayday, mayday, and atl approach advised fty was at my 9 O'clock position. I was given a heading of 180 degrees. By now, the engine was running fine, but I did not know why we had suffered the momentary power interruptions. Switched back to left main tanks, since I knew it was good. Broke out at 2700 ft MSL. Got a visual on fty. Changed to fty tower frequency 118.5. Tower cleared us to land on runway 8. However, in order to avoid landing with a left quartering tailwind, I requested a clearance to land on runway 32. After landing, taxied to FBO and discussed the situation with mr. X in maintenance and also with mr. Y at FBO. Since the airplane had just come out of maintenance, the left auxiliary tanks had been completely drained. Mr. Y suspected air in the lines. Mr. X and I carefully sumped the tanks and found only AVGAS. No water. No jet fuel. Did an extensive run-up and returned from fty to pdk. Will have aircraft checked by maintenance to verify there is nothing wrong with the fuel lines running from the left auxiliary tank. It appears to only have been a slug of air.

Original NASA ASRS Text

Title: EMER DECLARED WHEN ENG COUGHS AFTER SWITCHING FUEL TANKS.

Narrative: ENRTE TO FTY FOR PRACTICE ILS APCHS IN IMC. HAD JUST IDENTED FTY LOC, ATL VOR AND FLANC NDB AND HAD JUST GOTTEN FTY ATIS INFO. TOLD CFII ABOARD I WAS SWITCHING FROM L MAIN TO L AUX FUEL TANKS. ABOUT 15 SECONDS AFTER SWITCHING TANKS, THE ENG SUFFERED 2 MOMENTARY PWR INTERRUPTIONS. I IMMEDIATELY DECLARED MAYDAY, MAYDAY, MAYDAY, AND ATL APCH ADVISED FTY WAS AT MY 9 O'CLOCK POS. I WAS GIVEN A HDG OF 180 DEGS. BY NOW, THE ENG WAS RUNNING FINE, BUT I DID NOT KNOW WHY WE HAD SUFFERED THE MOMENTARY PWR INTERRUPTIONS. SWITCHED BACK TO L MAIN TANKS, SINCE I KNEW IT WAS GOOD. BROKE OUT AT 2700 FT MSL. GOT A VISUAL ON FTY. CHANGED TO FTY TWR FREQ 118.5. TWR CLRED US TO LAND ON RWY 8. HOWEVER, IN ORDER TO AVOID LNDG WITH A L QUARTERING TAILWIND, I REQUESTED A CLRNC TO LAND ON RWY 32. AFTER LNDG, TAXIED TO FBO AND DISCUSSED THE SIT WITH MR. X IN MAINT AND ALSO WITH MR. Y AT FBO. SINCE THE AIRPLANE HAD JUST COME OUT OF MAINT, THE L AUX TANKS HAD BEEN COMPLETELY DRAINED. MR. Y SUSPECTED AIR IN THE LINES. MR. X AND I CAREFULLY SUMPED THE TANKS AND FOUND ONLY AVGAS. NO WATER. NO JET FUEL. DID AN EXTENSIVE RUN-UP AND RETURNED FROM FTY TO PDK. WILL HAVE ACFT CHKED BY MAINT TO VERIFY THERE IS NOTHING WRONG WITH THE FUEL LINES RUNNING FROM THE L AUX TANK. IT APPEARS TO ONLY HAVE BEEN A SLUG OF AIR.

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.