Narrative:

Ord approach had cleared us for the runway 4R ILS, but maintain 250 KIAS until further advised. They also told us to contact tower 120.75 at rekks. I was hand flying the approach (the WX at ord was about 3000 ft overcast and 8 NM visibility) and it took me about 30 seconds to notice how quiet it had become on the ATC frequency, ie, it was totally silent! I looked down at communication #1 and we were on frequency 120.70 -- not correct! We were 20 mi outside rekks and should have still been on the TRACON frequency. It was gone forever (neither the first officer nor I had written it down anywhere), and I told him to tune in ord tower on 120.75. He did so, but couldn't contact them due to frequency congestion. In the meantime, I saw traffic (on TCASII) join the final 5 NM ahead of us. I extended the landing gear, slowed to 170 KIAS as quickly as I could to stay behind him. Then our dispatch called on the ACARS unit and said to contact TRACON O 128.45. We did -- the controller informed us she'd had to break traffic out of the approach because of our mistake. Things I learned: write down all frequency changes! Both pilots verify all communication changes on the radio immediately -- don't wait to notice how 'quiet' it has become! Callback conversation with reporter revealed the following information: the reporter stated that the first officer had pretuned the second communication tuning head to the tower frequency. When he then tuned the first head to the wrong frequency, the crew did not have access to the old frequency.

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Original NASA ASRS Text

Title: B737 CREW TUNES RADIO TO WRONG FREQ ON APCH TO ORD.

Narrative: ORD APCH HAD CLRED US FOR THE RWY 4R ILS, BUT MAINTAIN 250 KIAS UNTIL FURTHER ADVISED. THEY ALSO TOLD US TO CONTACT TWR 120.75 AT REKKS. I WAS HAND FLYING THE APCH (THE WX AT ORD WAS ABOUT 3000 FT OVCST AND 8 NM VISIBILITY) AND IT TOOK ME ABOUT 30 SECONDS TO NOTICE HOW QUIET IT HAD BECOME ON THE ATC FREQ, IE, IT WAS TOTALLY SILENT! I LOOKED DOWN AT COM #1 AND WE WERE ON FREQ 120.70 -- NOT CORRECT! WE WERE 20 MI OUTSIDE REKKS AND SHOULD HAVE STILL BEEN ON THE TRACON FREQ. IT WAS GONE FOREVER (NEITHER THE FO NOR I HAD WRITTEN IT DOWN ANYWHERE), AND I TOLD HIM TO TUNE IN ORD TWR ON 120.75. HE DID SO, BUT COULDN'T CONTACT THEM DUE TO FREQ CONGESTION. IN THE MEANTIME, I SAW TFC (ON TCASII) JOIN THE FINAL 5 NM AHEAD OF US. I EXTENDED THE LNDG GEAR, SLOWED TO 170 KIAS AS QUICKLY AS I COULD TO STAY BEHIND HIM. THEN OUR DISPATCH CALLED ON THE ACARS UNIT AND SAID TO CONTACT TRACON O 128.45. WE DID -- THE CTLR INFORMED US SHE'D HAD TO BREAK TFC OUT OF THE APCH BECAUSE OF OUR MISTAKE. THINGS I LEARNED: WRITE DOWN ALL FREQ CHANGES! BOTH PLTS VERIFY ALL COM CHANGES ON THE RADIO IMMEDIATELY -- DON'T WAIT TO NOTICE HOW 'QUIET' IT HAS BECOME! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT THE FO HAD PRETUNED THE SECOND COM TUNING HEAD TO THE TWR FREQ. WHEN HE THEN TUNED THE FIRST HEAD TO THE WRONG FREQ, THE CREW DID NOT HAVE ACCESS TO THE OLD FREQ.

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.