Small aircraft has clearance confusion begins takeoff without clearance.

Attributes
ACN	189204
Time
Date	199109
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : mem
State Reference	TN
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	climbout : takeoff ground : holding
Flight Plan	None
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : atp pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 75 flight time total : 6000 flight time type : 2000
ASRS Report	189204
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	incursion : runway non adherence : clearance non adherence : far other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

At holding area for 36R was given clearance to taxi into position and hold, then clearance was cancelled for wake turbulence (departing heavy jet). A few mins later I heard this: 'caution wake turbulence, cleared for takeoff runway 36R.' I proceeded to takeoff when I heard the controller say something like 'aircraft identification, hold' then hesitate and say 'never mind, cleared for takeoff.' later I was asked to call the tower and was told I had taken off without a proper clearance. The tower chief said the controller had intended to clear me for takeoff as he said 'caution wake turbulence' but changed his mind when told of a possible conflict. The statement 'caution wake turbulence' usually precedes takeoff clearance and that's what I heard. I should have read back what I thought I heard and the controller might have caught my mistake.

Original NASA ASRS Text

Title: SMA HAS CLRNC CONFUSION BEGINS TKOF WITHOUT CLRNC.

Narrative: AT HOLDING AREA FOR 36R WAS GIVEN CLRNC TO TAXI INTO POS AND HOLD, THEN CLRNC WAS CANCELLED FOR WAKE TURB (DEPARTING HVY JET). A FEW MINS LATER I HEARD THIS: 'CAUTION WAKE TURB, CLRED FOR TKOF RWY 36R.' I PROCEEDED TO TKOF WHEN I HEARD THE CTLR SAY SOMETHING LIKE 'ACFT ID, HOLD' THEN HESITATE AND SAY 'NEVER MIND, CLRED FOR TKOF.' LATER I WAS ASKED TO CALL THE TWR AND WAS TOLD I HAD TAKEN OFF WITHOUT A PROPER CLRNC. THE TWR CHIEF SAID THE CTLR HAD INTENDED TO CLR ME FOR TKOF AS HE SAID 'CAUTION WAKE TURB' BUT CHANGED HIS MIND WHEN TOLD OF A POSSIBLE CONFLICT. THE STATEMENT 'CAUTION WAKE TURB' USUALLY PRECEDES TKOF CLRNC AND THAT'S WHAT I HEARD. I SHOULD HAVE READ BACK WHAT I THOUGHT I HEARD AND THE CTLR MIGHT HAVE CAUGHT MY MISTAKE.

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.