Narrative:

We were on radar vectors to an ILS runway 23L approach at cle. Cleared to descend to 7000' on a 300 degree heading. The approach controller issued a clearance to turn to 320 degrees, slow to 170 KTS. At this point the clearance transmission was garbled, although it sounded like 'descend to (possibly) 4000.' we attempted to verify immediately; however, the controller was very busy and it took several requests before verification was received. While awaiting verification, we turned to 320 degrees and initiated confign changes required to slow to 170 KTS. When the controller verified the garbled clearance, he cleared us to turn to 320 degrees, then said, 'no, disregard, maintain your 300 degree heading, slow to 170 KTS, maintain 7000.' while turning to 320 degrees, configuring to reduce airspeed, attempting verification of the garbled clearance, and then turning back to the 300 degree heading, we inadvertently descended through 7000' to approximately 6725' (our altitude alert did not sound). The controller did not mention this deviation or any involvement of other aircraft. I do not know if we were cleared to a lower altitude in the garbled clearance, then reclred to maintain 7000', or the garbled clearance may have contained instructions other than a descent clearance. Under the existing conditions of heavy traffic, high and gusty winds, wind shear at the airport and turbulence aloft, a garbled multiple clearance, change of heading, change of airspeed, change of altitude, then a revised clearance back to the former heading, maintain 7000', both the flight crew and the controller were distracted at a critical time while under an unusually heavy workload. My suggestion for prevention of recurrence would be that controllers not issue clrncs calling for heading change, altitude change and airspeed change when the aircraft is on approach vectors. The crew is already involved with approach briefings, approach and landing checklists, aircraft confign changes, etc. Adding such multiple clrncs increases the probability of encountering a situation such as we experienced.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT. PIC COMPLAINS THAT MULTIPLE CLRNC INFORMATION CAUSED AMBIVALENCE AND POSSIBLE WRONG CLRNC INTERP.

Narrative: WE WERE ON RADAR VECTORS TO AN ILS RWY 23L APCH AT CLE. CLRED TO DSND TO 7000' ON A 300 DEG HDG. THE APCH CTLR ISSUED A CLRNC TO TURN TO 320 DEGS, SLOW TO 170 KTS. AT THIS POINT THE CLRNC XMISSION WAS GARBLED, ALTHOUGH IT SOUNDED LIKE 'DSND TO (POSSIBLY) 4000.' WE ATTEMPTED TO VERIFY IMMEDIATELY; HOWEVER, THE CTLR WAS VERY BUSY AND IT TOOK SEVERAL REQUESTS BEFORE VERIFICATION WAS RECEIVED. WHILE AWAITING VERIFICATION, WE TURNED TO 320 DEGS AND INITIATED CONFIGN CHANGES REQUIRED TO SLOW TO 170 KTS. WHEN THE CTLR VERIFIED THE GARBLED CLRNC, HE CLRED US TO TURN TO 320 DEGS, THEN SAID, 'NO, DISREGARD, MAINTAIN YOUR 300 DEG HDG, SLOW TO 170 KTS, MAINTAIN 7000.' WHILE TURNING TO 320 DEGS, CONFIGURING TO REDUCE AIRSPD, ATTEMPTING VERIFICATION OF THE GARBLED CLRNC, AND THEN TURNING BACK TO THE 300 DEG HDG, WE INADVERTENTLY DSNDED THROUGH 7000' TO APPROX 6725' (OUR ALT ALERT DID NOT SOUND). THE CTLR DID NOT MENTION THIS DEVIATION OR ANY INVOLVEMENT OF OTHER ACFT. I DO NOT KNOW IF WE WERE CLRED TO A LOWER ALT IN THE GARBLED CLRNC, THEN RECLRED TO MAINTAIN 7000', OR THE GARBLED CLRNC MAY HAVE CONTAINED INSTRUCTIONS OTHER THAN A DSCNT CLRNC. UNDER THE EXISTING CONDITIONS OF HEAVY TFC, HIGH AND GUSTY WINDS, WIND SHEAR AT THE ARPT AND TURB ALOFT, A GARBLED MULTIPLE CLRNC, CHANGE OF HDG, CHANGE OF AIRSPD, CHANGE OF ALT, THEN A REVISED CLRNC BACK TO THE FORMER HDG, MAINTAIN 7000', BOTH THE FLT CREW AND THE CTLR WERE DISTRACTED AT A CRITICAL TIME WHILE UNDER AN UNUSUALLY HEAVY WORKLOAD. MY SUGGESTION FOR PREVENTION OF RECURRENCE WOULD BE THAT CTLRS NOT ISSUE CLRNCS CALLING FOR HDG CHANGE, ALT CHANGE AND AIRSPD CHANGE WHEN THE ACFT IS ON APCH VECTORS. THE CREW IS ALREADY INVOLVED WITH APCH BRIEFINGS, APCH AND LNDG CHKLISTS, ACFT CONFIGN CHANGES, ETC. ADDING SUCH MULTIPLE CLRNCS INCREASES THE PROBABILITY OF ENCOUNTERING A SITUATION SUCH AS WE EXPERIENCED.

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.