Flight crew of an mdt descended below assigned crossing altitude due the first officer turning the altitude preselect knob instead of the desired airspeed setting knob of the flight guidance system. The first officer noticed his mistake and corrected back to assigned at once.

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Attributes
ACN	416600
Time
Date	199810
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : cvg
State Reference	OH
Altitude	msl bound lower : 10500 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute airway : cvg
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 16500 flight time type : 200
ASRS Report	416600
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : crossing restriction not met altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We had a clearance to cross tarne at 11000 ft and 250 KTS. The first officer was flying and had 11000 ft set in the altitude preselect. I was looking at the arrival chart and the approach plate as we neared 11000 ft. On this aircraft, the altitude select knob and the airspeed select knob look and feel similar. It was dark in the cockpit. As we approached 11000 ft, the first officer thought he had the airspeed knob and was trying to select 250 KTS, but was actually turning the altitude knob. The altitude preselect knob was inadvertently set to an altitude below 11000 ft, so we descended through 11000 ft. I looked up as we passed 11000 ft and the first officer caught it at the same time also. He immediately corrected, however, we descended to 10500 ft before we got the descent stopped. We had been handed off by center just prior to this, and checked in with approach after correcting the altitude. Nothing was said. I'll try to keep my head up as we approach assigned altitudes, and we'll both be more careful in programming the automation.

Original NASA ASRS Text

Title: FLC OF AN MDT DSNDED BELOW ASSIGNED XING ALT DUE THE FO TURNING THE ALT PRESELECT KNOB INSTEAD OF THE DESIRED AIRSPD SETTING KNOB OF THE FLT GUIDANCE SYS. THE FO NOTICED HIS MISTAKE AND CORRECTED BACK TO ASSIGNED AT ONCE.

Narrative: WE HAD A CLRNC TO CROSS TARNE AT 11000 FT AND 250 KTS. THE FO WAS FLYING AND HAD 11000 FT SET IN THE ALT PRESELECT. I WAS LOOKING AT THE ARR CHART AND THE APCH PLATE AS WE NEARED 11000 FT. ON THIS ACFT, THE ALT SELECT KNOB AND THE AIRSPD SELECT KNOB LOOK AND FEEL SIMILAR. IT WAS DARK IN THE COCKPIT. AS WE APCHED 11000 FT, THE FO THOUGHT HE HAD THE AIRSPD KNOB AND WAS TRYING TO SELECT 250 KTS, BUT WAS ACTUALLY TURNING THE ALT KNOB. THE ALT PRESELECT KNOB WAS INADVERTENTLY SET TO AN ALT BELOW 11000 FT, SO WE DSNDED THROUGH 11000 FT. I LOOKED UP AS WE PASSED 11000 FT AND THE FO CAUGHT IT AT THE SAME TIME ALSO. HE IMMEDIATELY CORRECTED, HOWEVER, WE DSNDED TO 10500 FT BEFORE WE GOT THE DSCNT STOPPED. WE HAD BEEN HANDED OFF BY CTR JUST PRIOR TO THIS, AND CHKED IN WITH APCH AFTER CORRECTING THE ALT. NOTHING WAS SAID. I'LL TRY TO KEEP MY HEAD UP AS WE APCH ASSIGNED ALTS, AND WE'LL BOTH BE MORE CAREFUL IN PROGRAMMING THE AUTOMATION.

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.