Narrative:

Aircraft #1 requested an IFR clearance to phx. He was off of sez a pop-up IFR. I gave him a code and idented him 5 mi south of sez. I asked him if he could maintain his own terrain and obstruction clearance 'to 11000 ft.' he said affirmative. I then cleared him to the phx airport via direct tonto and the fossl 3 arrival climb and 'maintain one, one -- eleven thousand, flg altimeter...' he then read back 'roger direct tonto, fossl 3 arrival, aircraft #1, uhh up to 16000 ft.' I said 'roger,' obviously not hearing the altitude readback. I then called traffic for aircraft #2 the aircraft that I stopped aircraft #1 for. Then I called traffic for aircraft #1 'traffic 12 O'clock position 4 mi 12000 ft a C172.' he said 'roger we're looking.' I then began giving a relief briefing when I noticed that aircraft #1 was at 11600 ft climbing. I asked him to verify level at 11000 ft, he said 'negative we read back 16000 ft.' his mode C now showed 12000 ft. I said 'negative your clearance was 11000 ft, but continue your climb, maintain 16000 ft, traffic 12 O'clock position 1 mi C172 at 12000 ft.' he said 'looking, sorry about that.'

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Original NASA ASRS Text

Title: LOSS OF SEPARATION BTWN AN AC69 AND A C172 AT 12000 FT WHEN RPTR MISSED THE INCORRECT ALT READBACK BY THE AC69 PLT OF 16000 FT VICE 11000 FT.

Narrative: ACFT #1 REQUESTED AN IFR CLRNC TO PHX. HE WAS OFF OF SEZ A POP-UP IFR. I GAVE HIM A CODE AND IDENTED HIM 5 MI S OF SEZ. I ASKED HIM IF HE COULD MAINTAIN HIS OWN TERRAIN AND OBSTRUCTION CLRNC 'TO 11000 FT.' HE SAID AFFIRMATIVE. I THEN CLRED HIM TO THE PHX ARPT VIA DIRECT TONTO AND THE FOSSL 3 ARR CLB AND 'MAINTAIN ONE, ONE -- ELEVEN THOUSAND, FLG ALTIMETER...' HE THEN READ BACK 'ROGER DIRECT TONTO, FOSSL 3 ARR, ACFT #1, UHH UP TO 16000 FT.' I SAID 'ROGER,' OBVIOUSLY NOT HEARING THE ALT READBACK. I THEN CALLED TFC FOR ACFT #2 THE ACFT THAT I STOPPED ACFT #1 FOR. THEN I CALLED TFC FOR ACFT #1 'TFC 12 O'CLOCK POS 4 MI 12000 FT A C172.' HE SAID 'ROGER WE'RE LOOKING.' I THEN BEGAN GIVING A RELIEF BRIEFING WHEN I NOTICED THAT ACFT #1 WAS AT 11600 FT CLBING. I ASKED HIM TO VERIFY LEVEL AT 11000 FT, HE SAID 'NEGATIVE WE READ BACK 16000 FT.' HIS MODE C NOW SHOWED 12000 FT. I SAID 'NEGATIVE YOUR CLRNC WAS 11000 FT, BUT CONTINUE YOUR CLB, MAINTAIN 16000 FT, TFC 12 O'CLOCK POS 1 MI C172 AT 12000 FT.' HE SAID 'LOOKING, SORRY ABOUT THAT.'

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.