Narrative:

I was working the local control position in a VFR tower. Small aircraft X had departed VFR eastbound off of runway 24L. X was told to make a right turn eastbound. Another cessna, Y called on frequency 10 mi east inbound about 3 min later, traffic was issued between X and Y. We were expecting a C130 in that morning and city operations had called asking if we knew where he was. I called the approach control and asked them if they had anything like that inbound. Approach said they were just about to call me with that inbound, and that he is 5 mi southeast. X then reported at 2500 ft requesting a frequency change, which was approved. The C130 then called on frequency and was told to report a 2 mi left base for runway 24R. I then issued traffic to Y inbound from the east who appeared to be on a dogleg to base entry for runway 24L. Y said he had the C130 in sight. Approach then calls over and says that the C130 has traffic ahead at 2500 ft. I then cleared the C130 to land on runway 24R. During his acknowledgement, he reported that a cessna had just passed him left to right about 100 ft above. The C130 was 2 mi south of the airport on a left base descending rapidly out of 3500 ft when this occurred. The aircraft was later idented as X by the C130 pilot. Several assumptions led to this occurrence. 1) the incident occurred 7 min after X departed the airport. Experience, as well as timing several other aircraft, indicate that departing runway 24L with a right turn northeast, east, or southeast requires 5 min to clear class D airspace and be at least 5 mi away, since 6-7 min had elapsed when X requested a frequency change, I believed him to be clear of the airspace. 2) both the C130 and the inbound cessna Y were in sight, as the C130 entered left base. The cessna was in close proximity on dog leg to base behind the C130. When traffic was passed from approach, I believed it to be in reference to the inbound cessna in close proximity to the C130, whom I had in sight and who had previously reported having the C130 in sight. 3) anticipating, believing , and assuming are almost the same thing.

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Original NASA ASRS Text

Title: MIL C130 HAD NMAC WITH SMA X IN CLASS D AIRSPACE. SEE AND AVOID CONCEPT.

Narrative: I WAS WORKING THE LCL CTL POS IN A VFR TWR. SMA X HAD DEPARTED VFR EBOUND OFF OF RWY 24L. X WAS TOLD TO MAKE A R TURN EBOUND. ANOTHER CESSNA, Y CALLED ON FREQ 10 MI E INBOUND ABOUT 3 MIN LATER, TFC WAS ISSUED BTWN X AND Y. WE WERE EXPECTING A C130 IN THAT MORNING AND CITY OPS HAD CALLED ASKING IF WE KNEW WHERE HE WAS. I CALLED THE APCH CTL AND ASKED THEM IF THEY HAD ANYTHING LIKE THAT INBOUND. APCH SAID THEY WERE JUST ABOUT TO CALL ME WITH THAT INBOUND, AND THAT HE IS 5 MI SE. X THEN RPTED AT 2500 FT REQUESTING A FREQ CHANGE, WHICH WAS APPROVED. THE C130 THEN CALLED ON FREQ AND WAS TOLD TO RPT A 2 MI L BASE FOR RWY 24R. I THEN ISSUED TFC TO Y INBOUND FROM THE E WHO APPEARED TO BE ON A DOGLEG TO BASE ENTRY FOR RWY 24L. Y SAID HE HAD THE C130 IN SIGHT. APCH THEN CALLS OVER AND SAYS THAT THE C130 HAS TFC AHEAD AT 2500 FT. I THEN CLRED THE C130 TO LAND ON RWY 24R. DURING HIS ACKNOWLEDGEMENT, HE RPTED THAT A CESSNA HAD JUST PASSED HIM L TO R ABOUT 100 FT ABOVE. THE C130 WAS 2 MI S OF THE ARPT ON A L BASE DSNDING RAPIDLY OUT OF 3500 FT WHEN THIS OCCURRED. THE ACFT WAS LATER IDENTED AS X BY THE C130 PLT. SEVERAL ASSUMPTIONS LED TO THIS OCCURRENCE. 1) THE INCIDENT OCCURRED 7 MIN AFTER X DEPARTED THE ARPT. EXPERIENCE, AS WELL AS TIMING SEVERAL OTHER ACFT, INDICATE THAT DEPARTING RWY 24L WITH A R TURN NE, E, OR SE REQUIRES 5 MIN TO CLR CLASS D AIRSPACE AND BE AT LEAST 5 MI AWAY, SINCE 6-7 MIN HAD ELAPSED WHEN X REQUESTED A FREQ CHANGE, I BELIEVED HIM TO BE CLR OF THE AIRSPACE. 2) BOTH THE C130 AND THE INBOUND CESSNA Y WERE IN SIGHT, AS THE C130 ENTERED L BASE. THE CESSNA WAS IN CLOSE PROX ON DOG LEG TO BASE BEHIND THE C130. WHEN TFC WAS PASSED FROM APCH, I BELIEVED IT TO BE IN REF TO THE INBOUND CESSNA IN CLOSE PROX TO THE C130, WHOM I HAD IN SIGHT AND WHO HAD PREVIOUSLY RPTED HAVING THE C130 IN SIGHT. 3) ANTICIPATING, BELIEVING , AND ASSUMING ARE ALMOST THE SAME THING.

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.