Narrative:

After departing sna airport and flying uneventfully up the coast, I acquired the current ATIS at lgb airport, contacted the tower and entered their airspace, joined left traffic and after a very extended downwind (tower called my base), I landed on runway 16L. Tower asked my destination on the airport and I replied an FBO on the west side. Tower then told me to turn right from the active runway 16L onto an inactive runway 25L, which I did. I'm not familiar with lgb airport but knew there were 5 crossing/intersecting runways (including a runway 16R staggered from runway 16L). Tower didn't advise me to contact ground (as I am used to) and since I was taxiing on an inactive runway, I assumed they wanted me on their frequency where I remained. I continued wbound on runway 25L looking for the FBO and unknowingly crossed active runway 16R without a clearance as an aircraft was completing a landing roll! I believe several factors compounded to this result: 1) runway 16R wasn't mentioned as in use in the ATIS. 2) an airship (to the west of me on final) was also on final with a destination between the runways, making me believe even more so that runway 16R was inactive. 3) taxiing on an inactive runway (ie, no hold short lines indicating an intersecting runway which I usually key on). 4) never hearing from the tower to either handoff to ground or to hold short of runway 16R. 5) seeing the other aircraft in the distance, but assumed it was also taxiing. Tower was busy, but in retrospect, I should have verified intentions with them before that much time elapsed. Still don't know why they didn't call me (probably were via ground!) before we resulted in a loss of separation, but I'll know soon -- I've been invited to a 'pilot deviation' inquiry! Moral: don't assume. I think we all know what it does.

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Original NASA ASRS Text

Title: AFTER LNDG AT LGB, C150 TAXIED TOWARD RAMP AND CROSSED AN ACTIVE RWY WITHOUT CLRNC.

Narrative: AFTER DEPARTING SNA ARPT AND FLYING UNEVENTFULLY UP THE COAST, I ACQUIRED THE CURRENT ATIS AT LGB ARPT, CONTACTED THE TWR AND ENTERED THEIR AIRSPACE, JOINED L TFC AND AFTER A VERY EXTENDED DOWNWIND (TWR CALLED MY BASE), I LANDED ON RWY 16L. TWR ASKED MY DEST ON THE ARPT AND I REPLIED AN FBO ON THE W SIDE. TWR THEN TOLD ME TO TURN R FROM THE ACTIVE RWY 16L ONTO AN INACTIVE RWY 25L, WHICH I DID. I'M NOT FAMILIAR WITH LGB ARPT BUT KNEW THERE WERE 5 XING/INTERSECTING RWYS (INCLUDING A RWY 16R STAGGERED FROM RWY 16L). TWR DIDN'T ADVISE ME TO CONTACT GND (AS I AM USED TO) AND SINCE I WAS TAXIING ON AN INACTIVE RWY, I ASSUMED THEY WANTED ME ON THEIR FREQ WHERE I REMAINED. I CONTINUED WBOUND ON RWY 25L LOOKING FOR THE FBO AND UNKNOWINGLY CROSSED ACTIVE RWY 16R WITHOUT A CLRNC AS AN ACFT WAS COMPLETING A LNDG ROLL! I BELIEVE SEVERAL FACTORS COMPOUNDED TO THIS RESULT: 1) RWY 16R WASN'T MENTIONED AS IN USE IN THE ATIS. 2) AN AIRSHIP (TO THE W OF ME ON FINAL) WAS ALSO ON FINAL WITH A DEST BTWN THE RWYS, MAKING ME BELIEVE EVEN MORE SO THAT RWY 16R WAS INACTIVE. 3) TAXIING ON AN INACTIVE RWY (IE, NO HOLD SHORT LINES INDICATING AN INTERSECTING RWY WHICH I USUALLY KEY ON). 4) NEVER HEARING FROM THE TWR TO EITHER HDOF TO GND OR TO HOLD SHORT OF RWY 16R. 5) SEEING THE OTHER ACFT IN THE DISTANCE, BUT ASSUMED IT WAS ALSO TAXIING. TWR WAS BUSY, BUT IN RETROSPECT, I SHOULD HAVE VERIFIED INTENTIONS WITH THEM BEFORE THAT MUCH TIME ELAPSED. STILL DON'T KNOW WHY THEY DIDN'T CALL ME (PROBABLY WERE VIA GND!) BEFORE WE RESULTED IN A LOSS OF SEPARATION, BUT I'LL KNOW SOON -- I'VE BEEN INVITED TO A 'PLTDEV' INQUIRY! MORAL: DON'T ASSUME. I THINK WE ALL KNOW WHAT IT DOES.

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.