Narrative:

I was working combined arrival/departure control at mke TRACON. My relief had just plugged into the position, and I was giving my position relief briefing as the following occurred. Air carrier X departed mke and was climbed to 11000'. A few mins later, air carrier xx departed. I saw his transponder acquire on my ARTS radar, but the flight had not checked in. Meanwhile, I told air carrier X to contact ZAU on 132.3. 2 aircraft obviously acknowledged the transmission, followed by 'air carrier X leaving eighteen hundred.' air carrier X was actually leaving 8000', but I observed air carrier xx leaving 1800'. I said, 'is that air carrier xx calling mke?' no answer. I tried again to call air carrier xx, west/O success. The tower,, who had routinely cleared air carrier xx to 5000', made unsuccessful attempts to contact him. In the meantime, my relief had taken over the position. Before unplugging completely, I stood up and moved to a coordination position to call ZAU. I told them I believed air carrier xx had taken another aircraft's call and was likely on their frequency. I asked them to attempt calling air carrier xx. They replied they were talking to him, had climbed him to 12000', and were requesting control for on course! I immediately checked the radar and saw air carrier Y less than 1 mi from air carrier xx on a downwind. Air carrier Y was at 7000' level, air carrier xx at 6800' climbing, but already through air carrier Y's course. I advised ZAU that mke radar had never made contact with air carrier xx. The mke ARTS program has an automatic-handoff feature whereby handoffs to ZAU are automatically initiated when a departure leaves 2000'. Air carrier xx handoff had been accepted by ZAU, so when he called them 'leaving 4000,' they assumed he was climbing to 11000' as specified in our letter of agreement. We at mke assumed he was climbing to 5000', since this was his last known clearance. When we talked to air carrier xx captain, he said he thought at the time it was somewhat odd that he was told to contact ZAU when he had just changed the radio over to mke departure frequency. He did not realize he called himself air carrier X. Neither he nor air carrier Y mentioned the proximity of the other. Problems: 1) similar call signs. 2) if air carrier xx had told ZAU he was out of 4000 for 5000', they would have been alerted similarly, they might have questioned his last clearance. 3) automatic-handoff is initiated too early. No time to ensure control by departure. How would you apportion the blame for this near fiasco?

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR RESPONDED TO ANOTHER ACR'S CLRNC FOR FREQ CHANGE THEREBY CAUSING A CONFLICTION WITH ANOTHER ACFT.

Narrative: I WAS WORKING COMBINED ARR/DEP CTL AT MKE TRACON. MY RELIEF HAD JUST PLUGGED INTO THE POS, AND I WAS GIVING MY POS RELIEF BRIEFING AS THE FOLLOWING OCCURRED. ACR X DEPARTED MKE AND WAS CLBED TO 11000'. A FEW MINS LATER, ACR XX DEPARTED. I SAW HIS XPONDER ACQUIRE ON MY ARTS RADAR, BUT THE FLT HAD NOT CHKED IN. MEANWHILE, I TOLD ACR X TO CONTACT ZAU ON 132.3. 2 ACFT OBVIOUSLY ACKNOWLEDGED THE XMISSION, FOLLOWED BY 'ACR X LEAVING EIGHTEEN HUNDRED.' ACR X WAS ACTUALLY LEAVING 8000', BUT I OBSERVED ACR XX LEAVING 1800'. I SAID, 'IS THAT ACR XX CALLING MKE?' NO ANSWER. I TRIED AGAIN TO CALL ACR XX, W/O SUCCESS. THE TWR,, WHO HAD ROUTINELY CLRED ACR XX TO 5000', MADE UNSUCCESSFUL ATTEMPTS TO CONTACT HIM. IN THE MEANTIME, MY RELIEF HAD TAKEN OVER THE POS. BEFORE UNPLUGGING COMPLETELY, I STOOD UP AND MOVED TO A COORD POS TO CALL ZAU. I TOLD THEM I BELIEVED ACR XX HAD TAKEN ANOTHER ACFT'S CALL AND WAS LIKELY ON THEIR FREQ. I ASKED THEM TO ATTEMPT CALLING ACR XX. THEY REPLIED THEY WERE TALKING TO HIM, HAD CLBED HIM TO 12000', AND WERE REQUESTING CTL FOR ON COURSE! I IMMEDIATELY CHKED THE RADAR AND SAW ACR Y LESS THAN 1 MI FROM ACR XX ON A DOWNWIND. ACR Y WAS AT 7000' LEVEL, ACR XX AT 6800' CLBING, BUT ALREADY THROUGH ACR Y'S COURSE. I ADVISED ZAU THAT MKE RADAR HAD NEVER MADE CONTACT WITH ACR XX. THE MKE ARTS PROGRAM HAS AN AUTO-HDOF FEATURE WHEREBY HDOFS TO ZAU ARE AUTOMATICALLY INITIATED WHEN A DEP LEAVES 2000'. ACR XX HDOF HAD BEEN ACCEPTED BY ZAU, SO WHEN HE CALLED THEM 'LEAVING 4000,' THEY ASSUMED HE WAS CLBING TO 11000' AS SPECIFIED IN OUR LETTER OF AGREEMENT. WE AT MKE ASSUMED HE WAS CLBING TO 5000', SINCE THIS WAS HIS LAST KNOWN CLRNC. WHEN WE TALKED TO ACR XX CAPT, HE SAID HE THOUGHT AT THE TIME IT WAS SOMEWHAT ODD THAT HE WAS TOLD TO CONTACT ZAU WHEN HE HAD JUST CHANGED THE RADIO OVER TO MKE DEP FREQ. HE DID NOT REALIZE HE CALLED HIMSELF ACR X. NEITHER HE NOR ACR Y MENTIONED THE PROX OF THE OTHER. PROBS: 1) SIMILAR CALL SIGNS. 2) IF ACR XX HAD TOLD ZAU HE WAS OUT OF 4000 FOR 5000', THEY WOULD HAVE BEEN ALERTED SIMILARLY, THEY MIGHT HAVE QUESTIONED HIS LAST CLRNC. 3) AUTO-HDOF IS INITIATED TOO EARLY. NO TIME TO ENSURE CTL BY DEP. HOW WOULD YOU APPORTION THE BLAME FOR THIS NEAR FIASCO?

Data retrieved from NASA's ASRS site as of August 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.