Narrative:

We were flying the expressway visual runway 31 lga and were following traffic pointed out to us. Passing over dials, the captain called for the gear, flaps and landing checklist. About the same time, tower told us we were cleared to land and that there would be a departure off runway 4 prior to our arrival. I finished the landing checklist, extended the runway centerline on the FMS, checked the commercial chart pages to see what the recommended turn to final altitude was. When I looked up, I saw what I thought was our interval over the threshold and stated, 'this will work out fine' (for the runway 4 departure). As we started our turn to final, the tower said we were cutting out our interval and for us to continue to land and for them to go around. In fact, when I looked well off to our right, an MD80 was turning a deep final, no evasive action was required other than the go around. The only link in the chain that I can see that might have prevented this (and it's a big one) was when we were given our traffic to follow, I was so busy I didn't 'process' the information. When I looked up and saw our 'interval' over the threshold, it was a turboprop. Our real interval was an MD80. A valuable lesson that some information, when missed because of being loaded up, needs to be ascertained rather than assuming what you 'see' makes sense.

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Original NASA ASRS Text

Title: AN ACR FO PNF MISTOOK DEPARTING TFC AT LGA AS THE TFC HE WAS FOLLOWING IN ON THE VISUAL APCH. THINKING THE TFC HE WAS FOLLOWING WAS OVER THE THRESHOLD, HE ALLOWED THE PF TO TURN FINAL, THEREBY CUTTING OFF THE MD80 THEY WERE SUPPOSED TO MAINTAIN VISUAL WITH.

Narrative: WE WERE FLYING THE EXPRESSWAY VISUAL RWY 31 LGA AND WERE FOLLOWING TFC POINTED OUT TO US. PASSING OVER DIALS, THE CAPT CALLED FOR THE GEAR, FLAPS AND LNDG CHKLIST. ABOUT THE SAME TIME, TWR TOLD US WE WERE CLRED TO LAND AND THAT THERE WOULD BE A DEP OFF RWY 4 PRIOR TO OUR ARR. I FINISHED THE LNDG CHKLIST, EXTENDED THE RWY CTRLINE ON THE FMS, CHKED THE COMMERCIAL CHART PAGES TO SEE WHAT THE RECOMMENDED TURN TO FINAL ALT WAS. WHEN I LOOKED UP, I SAW WHAT I THOUGHT WAS OUR INTERVAL OVER THE THRESHOLD AND STATED, 'THIS WILL WORK OUT FINE' (FOR THE RWY 4 DEP). AS WE STARTED OUR TURN TO FINAL, THE TWR SAID WE WERE CUTTING OUT OUR INTERVAL AND FOR US TO CONTINUE TO LAND AND FOR THEM TO GO AROUND. IN FACT, WHEN I LOOKED WELL OFF TO OUR R, AN MD80 WAS TURNING A DEEP FINAL, NO EVASIVE ACTION WAS REQUIRED OTHER THAN THE GAR. THE ONLY LINK IN THE CHAIN THAT I CAN SEE THAT MIGHT HAVE PREVENTED THIS (AND IT'S A BIG ONE) WAS WHEN WE WERE GIVEN OUR TFC TO FOLLOW, I WAS SO BUSY I DIDN'T 'PROCESS' THE INFO. WHEN I LOOKED UP AND SAW OUR 'INTERVAL' OVER THE THRESHOLD, IT WAS A TURBOPROP. OUR REAL INTERVAL WAS AN MD80. A VALUABLE LESSON THAT SOME INFO, WHEN MISSED BECAUSE OF BEING LOADED UP, NEEDS TO BE ASCERTAINED RATHER THAN ASSUMING WHAT YOU 'SEE' MAKES SENSE.

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.