Narrative:

Lax approach informed us that we would 'follow an medium large transport coming from the north side on right downwind.' we gained visibility sighting of the medium large transport as it turned right base to final for 25L. Approach issued us a clearance to, 'maintain visibility with the medium large transport, he is for 25L, you are cleared visibility for 25R.' the medium large transport was approximately 2-3 mi ahead. At about 3 mi out I overheard lax tower discussing with air carrier Y that traffic ahead was '120 KTS.' a couple of transmission followed between the tower and the 'other' aircraft. Then both of us saw air carrier Y medium large transport overfly us by not more than 250' vertical sep. The tower did not issue traffic. Air carrier Y descended through our altitude of 800' MSL, horizontal sep appeared to be 700'. It became clear in just a few seconds that air carrier Y was descending faster than us and was to pose a wake turbulence problem for us. I called for an immediate right turn and missed approach. We then informed the tower of our intentions. Air carrier Y was unable to land on 25L as a result of closing too fast on the medium large transport. It appears to me that air carrier Y was intending to land on 25R until the tower instructed air carrier Y to land on 25L. It was at that time that the air carrier Y started to turn left toward 25L and overfly us. The second time around, we were cleared for a visibility to 25L. We switched to the tower and received landing clearance. At about 1500' MSL the tower issued us a warning of converging traffic from the north complex that had overshot the 24's. Air carrier Z light transport was spotted in our 2 O'clock position, about 700' away and at the same altitude moving about 10 KTS faster. His bank angle, at the time, of 30-40 degrees, suggests that it came as close as 200' horizontal sep. Air carrier Z, landing on the 24's, was on another frequency, and so we could not hear any of its transmission. We continued our approach and landed west/O further incident. I called lax TRACON and talked to FAA supervisor who told me air carrier Y crew had understood that they had been cleared to 25R. He said that the matter would B turned over to quality control the following day. When mentioned the air carrier Z incident, he said he would have to get back to me. Supplemental information from acn 139173: comment: it appeared that for both incidents the tower's ability to resolve traffic conflict by both visibility and radar interpretations was inadequate. Other contributing factors were that of both aircraft crews to accurately follow ATC instructions, and to fly precise courses to assigned runways. In addition pilot clearance readback for landing clrncs should always include runway # and state left or right. Phrases such as, 'understand cleared to land,' etc, are not precise and clear enough to detect any misunderstanding between ATC and flight crews.

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Original NASA ASRS Text

Title: ACR Y AND Z TRACK DEVIATION HAD NMAC WITH ACR X. PLT DEVIATION.

Narrative: LAX APCH INFORMED US THAT WE WOULD 'FOLLOW AN MLG COMING FROM THE N SIDE ON RIGHT DOWNWIND.' WE GAINED VIS SIGHTING OF THE MLG AS IT TURNED RIGHT BASE TO FINAL FOR 25L. APCH ISSUED US A CLRNC TO, 'MAINTAIN VIS WITH THE MLG, HE IS FOR 25L, YOU ARE CLRED VIS FOR 25R.' THE MLG WAS APPROX 2-3 MI AHEAD. AT ABOUT 3 MI OUT I OVERHEARD LAX TWR DISCUSSING WITH ACR Y THAT TFC AHEAD WAS '120 KTS.' A COUPLE OF XMISSION FOLLOWED BTWN THE TWR AND THE 'OTHER' ACFT. THEN BOTH OF US SAW ACR Y MLG OVERFLY US BY NOT MORE THAN 250' VERT SEP. THE TWR DID NOT ISSUE TFC. ACR Y DSNDED THROUGH OUR ALT OF 800' MSL, HORIZ SEP APPEARED TO BE 700'. IT BECAME CLR IN JUST A FEW SECS THAT ACR Y WAS DSNDING FASTER THAN US AND WAS TO POSE A WAKE TURB PROB FOR US. I CALLED FOR AN IMMEDIATE RIGHT TURN AND MISSED APCH. WE THEN INFORMED THE TWR OF OUR INTENTIONS. ACR Y WAS UNABLE TO LAND ON 25L AS A RESULT OF CLOSING TOO FAST ON THE MLG. IT APPEARS TO ME THAT ACR Y WAS INTENDING TO LAND ON 25R UNTIL THE TWR INSTRUCTED ACR Y TO LAND ON 25L. IT WAS AT THAT TIME THAT THE ACR Y STARTED TO TURN LEFT TOWARD 25L AND OVERFLY US. THE SECOND TIME AROUND, WE WERE CLRED FOR A VIS TO 25L. WE SWITCHED TO THE TWR AND RECEIVED LNDG CLRNC. AT ABOUT 1500' MSL THE TWR ISSUED US A WARNING OF CONVERGING TFC FROM THE N COMPLEX THAT HAD OVERSHOT THE 24'S. ACR Z LTT WAS SPOTTED IN OUR 2 O'CLOCK POS, ABOUT 700' AWAY AND AT THE SAME ALT MOVING ABOUT 10 KTS FASTER. HIS BANK ANGLE, AT THE TIME, OF 30-40 DEGS, SUGGESTS THAT IT CAME AS CLOSE AS 200' HORIZ SEP. ACR Z, LNDG ON THE 24'S, WAS ON ANOTHER FREQ, AND SO WE COULD NOT HEAR ANY OF ITS XMISSION. WE CONTINUED OUR APCH AND LANDED W/O FURTHER INCIDENT. I CALLED LAX TRACON AND TALKED TO FAA SUPVR WHO TOLD ME ACR Y CREW HAD UNDERSTOOD THAT THEY HAD BEEN CLRED TO 25R. HE SAID THAT THE MATTER WOULD B TURNED OVER TO QUALITY CONTROL THE FOLLOWING DAY. WHEN MENTIONED THE ACR Z INCIDENT, HE SAID HE WOULD HAVE TO GET BACK TO ME. SUPPLEMENTAL INFO FROM ACN 139173: COMMENT: IT APPEARED THAT FOR BOTH INCIDENTS THE TWR'S ABILITY TO RESOLVE TFC CONFLICT BY BOTH VIS AND RADAR INTERPRETATIONS WAS INADEQUATE. OTHER CONTRIBUTING FACTORS WERE THAT OF BOTH ACFT CREWS TO ACCURATELY FOLLOW ATC INSTRUCTIONS, AND TO FLY PRECISE COURSES TO ASSIGNED RWYS. IN ADDITION PLT CLRNC READBACK FOR LNDG CLRNCS SHOULD ALWAYS INCLUDE RWY # AND STATE LEFT OR RIGHT. PHRASES SUCH AS, 'UNDERSTAND CLRED TO LAND,' ETC, ARE NOT PRECISE AND CLEAR ENOUGH TO DETECT ANY MISUNDERSTANDING BTWN ATC AND FLT CREWS.

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.