Pilot of a C172 took off without clearance due to a misunderstanding of ATC instructions.

Attributes
ACN	368730
Time
Date	199705
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : mso
State Reference	MT
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	climbout : takeoff ground : holding
Flight Plan	None
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	landing other
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : atp pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 40 flight time total : 10000 flight time type : 700
ASRS Report	368730
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	incursion : runway non adherence : far other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Possible air traffic conflict. I was cleared for takeoff on runway 25 at missoula county airport, mt, on may/wed/97, at approximately XB05 local, received a TA of landing traffic on runway 29. I rechked with tower and understood I was cleared for takeoff. I did not receive 'hold your position' instructions. I departed on runway 25 and after takeoff I was advised by tower that I had not been cleared for takeoff. I saw no other traffic on departure. Onboard with me was my wife. If there was a misunderstanding I believe it to have been caused by non standard ATC instructions.

Original NASA ASRS Text

Title: PLT OF A C172 TOOK OFF WITHOUT CLRNC DUE TO A MISUNDERSTANDING OF ATC INSTRUCTIONS.

Narrative: POSSIBLE AIR TFC CONFLICT. I WAS CLRED FOR TKOF ON RWY 25 AT MISSOULA COUNTY ARPT, MT, ON MAY/WED/97, AT APPROX XB05 LCL, RECEIVED A TA OF LNDG TFC ON RWY 29. I RECHKED WITH TWR AND UNDERSTOOD I WAS CLRED FOR TKOF. I DID NOT RECEIVE 'HOLD YOUR POS' INSTRUCTIONS. I DEPARTED ON RWY 25 AND AFTER TKOF I WAS ADVISED BY TWR THAT I HAD NOT BEEN CLRED FOR TKOF. I SAW NO OTHER TFC ON DEP. ONBOARD WITH ME WAS MY WIFE. IF THERE WAS A MISUNDERSTANDING I BELIEVE IT TO HAVE BEEN CAUSED BY NON STANDARD ATC INSTRUCTIONS.

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.