Narrative:

While cruising at FL230, center issued a clearance to cross 45 west of iiu at/maintain 11000' and 250 KTS. The captain was flying and he immediately began a descent to make the close restriction. I (the first officer) mis-set the altitude alert to 10000'. The captain and F/east failed to catch this error. At approximately 12000', center issued a frequency change to louisville approach. I made the required '11 for 10' callout, then proceeded to contact louisville approach. As I reported 'out of 1-0-thousand, 5 hundred, for 1-0-thousand,' all 3 crew members suddenly questioned the 10000' clearance. The captain immediately leveled off as I made 2 additional attempts to clarify the clearance with louisville approach. Following the second transmission, approach replied, 'roger, that was 11. Descend and maintain 6000.' I replied, 'roger, we're leaving 1-1-thousand for 6.' no more was said by approach control. For some reason, we all had 10000' in our heads and do not blame that on the altitude alert being set improperly. We think the 250 KT restriction could have led us to assume 10000', because the majority of locations use 10000'/250 KTS xings in their stars. This airport had not published STAR. These multi-faceted clrncs are an accident waiting to happen. Far too many variables are given all in one fast sentence. Example: 'xyz 123 cross 110 mi southeast of nashville at and maintain 1-3-thousand, 2-5-0 KTS, chattanooga altimeter 3-0-1-3.' our company policy requires that we repeat the entire clearance, including the altimeter setting. That can be quite a few #'south to boggle. We still are not sure if we were given 11000' or 10000' in our original clearance. Something needs to be done to avoid the confusion between 11000' and 10000' crossing clrncs. We are not the first to fall into this trap, nor is this the first time it has almost happened to me.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR DESCENDED APPROX 600' BELOW ASSIGNED ALT OF 11000'.

Narrative: WHILE CRUISING AT FL230, CENTER ISSUED A CLRNC TO CROSS 45 W OF IIU AT/MAINTAIN 11000' AND 250 KTS. THE CAPT WAS FLYING AND HE IMMEDIATELY BEGAN A DSCNT TO MAKE THE CLOSE RESTRICTION. I (THE F/O) MIS-SET THE ALT ALERT TO 10000'. THE CAPT AND F/E FAILED TO CATCH THIS ERROR. AT APPROX 12000', CENTER ISSUED A FREQ CHANGE TO LOUISVILLE APCH. I MADE THE REQUIRED '11 FOR 10' CALLOUT, THEN PROCEEDED TO CONTACT LOUISVILLE APCH. AS I RPTED 'OUT OF 1-0-THOUSAND, 5 HUNDRED, FOR 1-0-THOUSAND,' ALL 3 CREW MEMBERS SUDDENLY QUESTIONED THE 10000' CLRNC. THE CAPT IMMEDIATELY LEVELED OFF AS I MADE 2 ADDITIONAL ATTEMPTS TO CLARIFY THE CLRNC WITH LOUISVILLE APCH. FOLLOWING THE SECOND XMISSION, APCH REPLIED, 'ROGER, THAT WAS 11. DSND AND MAINTAIN 6000.' I REPLIED, 'ROGER, WE'RE LEAVING 1-1-THOUSAND FOR 6.' NO MORE WAS SAID BY APCH CTL. FOR SOME REASON, WE ALL HAD 10000' IN OUR HEADS AND DO NOT BLAME THAT ON THE ALT ALERT BEING SET IMPROPERLY. WE THINK THE 250 KT RESTRICTION COULD HAVE LED US TO ASSUME 10000', BECAUSE THE MAJORITY OF LOCATIONS USE 10000'/250 KTS XINGS IN THEIR STARS. THIS ARPT HAD NOT PUBLISHED STAR. THESE MULTI-FACETED CLRNCS ARE AN ACCIDENT WAITING TO HAPPEN. FAR TOO MANY VARIABLES ARE GIVEN ALL IN ONE FAST SENTENCE. EXAMPLE: 'XYZ 123 CROSS 110 MI SE OF NASHVILLE AT AND MAINTAIN 1-3-THOUSAND, 2-5-0 KTS, CHATTANOOGA ALTIMETER 3-0-1-3.' OUR COMPANY POLICY REQUIRES THAT WE REPEAT THE ENTIRE CLRNC, INCLUDING THE ALTIMETER SETTING. THAT CAN BE QUITE A FEW #'S TO BOGGLE. WE STILL ARE NOT SURE IF WE WERE GIVEN 11000' OR 10000' IN OUR ORIGINAL CLRNC. SOMETHING NEEDS TO BE DONE TO AVOID THE CONFUSION BTWN 11000' AND 10000' XING CLRNCS. WE ARE NOT THE FIRST TO FALL INTO THIS TRAP, NOR IS THIS THE FIRST TIME IT HAS ALMOST HAPPENED TO ME.

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.