Narrative:

I undertook a pleasure flight from ZZZ to ZZZ1 with 1 passenger. The WX was clear and VMC. Because the GPS in the aircraft I was using had an expired database; I planned to use 2 onboard VOR receivers for primary navigation and the GPS for backup. I filed an IFR flight plan for a cessna '172/U.' the initial part of my flight plan was ZZZ to the intersection; thence V97 to the ZZZ4 VOR. I set one VOR receiver to the VOR and the second to the ZZZ4 VOR. I set the GPS to indicate a direct track between ZZZ and the intersection. The duats flight plan I printed out that morning indicated a heading of 017 degrees to the intersection. The L-22 IFR en route low altitude chart depicts the intersection as being located on the 350 degree radial of ZZZ3 and the 174 degree radial of ZZZ4. I was cleared 'as filed' to ZZZ1. I was cleared for takeoff on a heading of 360 degrees from the A1 intersection of runway 4. An airliner was holding near the threshold of runway 4; clear of a construction area. After changing frequencys from tower to departure; I was instructed to intercept the 335 degree radial of ZZZ3 and climb to my en route altitude of 6000 ft. I dialed in the 335 degree radial of ZZZ3 and after a brief time turned toward a heading of about 050 degrees to intercept the radial. The controller asked why I had turned and demanded to know whether I had understood his instruction to fly a heading of 360 degrees to intercept the 335 degree radial of ZZZ3. He said my turn was taking me toward departing traffic. I apologized for my misunderstanding and complied with the new instruction to turn to a heading of 270 degrees until traffic was clear of the area. I did not intentionally ignore the controller's instructions. Although the departure heading I was initially assigned was 360 degrees; I thought -- mistakenly; it now appears -- that I was cleared to turn to a heading that would intercept the 335 degree radial more promptly after I was told to intercept that radial. In the future; I will probably ask for verification of a clearance before I turn toward an assigned radial. I tried to plan this flight carefully; but apparently my situational awareness lagged behind the instructions I received during climb out.

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Original NASA ASRS Text

Title: A C172 DEPARTING ON AN IFR FLT PLAN DEVIATED FROM A VECTOR HDG AND FLEW TOWARD DEPARTING TFC.

Narrative: I UNDERTOOK A PLEASURE FLT FROM ZZZ TO ZZZ1 WITH 1 PAX. THE WX WAS CLR AND VMC. BECAUSE THE GPS IN THE ACFT I WAS USING HAD AN EXPIRED DATABASE; I PLANNED TO USE 2 ONBOARD VOR RECEIVERS FOR PRIMARY NAV AND THE GPS FOR BACKUP. I FILED AN IFR FLT PLAN FOR A CESSNA '172/U.' THE INITIAL PART OF MY FLT PLAN WAS ZZZ TO THE INTXN; THENCE V97 TO THE ZZZ4 VOR. I SET ONE VOR RECEIVER TO THE VOR AND THE SECOND TO THE ZZZ4 VOR. I SET THE GPS TO INDICATE A DIRECT TRACK BTWN ZZZ AND THE INTXN. THE DUATS FLT PLAN I PRINTED OUT THAT MORNING INDICATED A HDG OF 017 DEGS TO THE INTXN. THE L-22 IFR ENRTE LOW ALT CHART DEPICTS THE INTXN AS BEING LOCATED ON THE 350 DEG RADIAL OF ZZZ3 AND THE 174 DEG RADIAL OF ZZZ4. I WAS CLRED 'AS FILED' TO ZZZ1. I WAS CLRED FOR TKOF ON A HDG OF 360 DEGS FROM THE A1 INTXN OF RWY 4. AN AIRLINER WAS HOLDING NEAR THE THRESHOLD OF RWY 4; CLR OF A CONSTRUCTION AREA. AFTER CHANGING FREQS FROM TWR TO DEP; I WAS INSTRUCTED TO INTERCEPT THE 335 DEG RADIAL OF ZZZ3 AND CLB TO MY ENRTE ALT OF 6000 FT. I DIALED IN THE 335 DEG RADIAL OF ZZZ3 AND AFTER A BRIEF TIME TURNED TOWARD A HDG OF ABOUT 050 DEGS TO INTERCEPT THE RADIAL. THE CTLR ASKED WHY I HAD TURNED AND DEMANDED TO KNOW WHETHER I HAD UNDERSTOOD HIS INSTRUCTION TO FLY A HDG OF 360 DEGS TO INTERCEPT THE 335 DEG RADIAL OF ZZZ3. HE SAID MY TURN WAS TAKING ME TOWARD DEPARTING TFC. I APOLOGIZED FOR MY MISUNDERSTANDING AND COMPLIED WITH THE NEW INSTRUCTION TO TURN TO A HDG OF 270 DEGS UNTIL TFC WAS CLR OF THE AREA. I DID NOT INTENTIONALLY IGNORE THE CTLR'S INSTRUCTIONS. ALTHOUGH THE DEP HDG I WAS INITIALLY ASSIGNED WAS 360 DEGS; I THOUGHT -- MISTAKENLY; IT NOW APPEARS -- THAT I WAS CLRED TO TURN TO A HDG THAT WOULD INTERCEPT THE 335 DEG RADIAL MORE PROMPTLY AFTER I WAS TOLD TO INTERCEPT THAT RADIAL. IN THE FUTURE; I WILL PROBABLY ASK FOR VERIFICATION OF A CLRNC BEFORE I TURN TOWARD AN ASSIGNED RADIAL. I TRIED TO PLAN THIS FLT CAREFULLY; BUT APPARENTLY MY SITUATIONAL AWARENESS LAGGED BEHIND THE INSTRUCTIONS I RECEIVED DURING CLBOUT.

Data retrieved from NASA's ASRS site as of January 2009 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.