Distraction flight crew of BE02 erroneously descended below assigned altitude on arrival to cos, co.

Attributes
ACN	424070
Time
Date	199812
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : brk
State Reference	CO
Altitude	msl bound lower : 10000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Operator	common carrier : air carrier
Flight Phase	cruise other descent other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 200 flight time total : 4100 flight time type : 3800
ASRS Report	424070
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 187 flight time total : 1644 flight time type : 1312
ASRS Report	424849
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude altitude deviation : crossing restriction not met non adherence : far other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated faa : reviewed incident with flight crew
Supplementary
Air Traffic Incident	Pilot Deviation

Narrative:

I was captain en route from abq to cos. From our en route altitude we had been cleared to descend to 17000 ft then pilot's discretion to 13000 ft to cross 35 mi south of black forest VOR at 13000 ft. Our aircraft had been experiencing mode C problems with our transponder and was sending erroneous information to ZDV. Center was aware of the situation. At the time of our clearance to descend, I pressed the test button on our transponder and it was encoding approximately 10000 ft erroneously. I mistakenly put 10000 ft in our altitude selector. When center handed us off to cos approach, I reported our altitude and was asked to repeat it. I repeated our altitude without thinking about it and on final to runway 35R in cos I realized what I had done and why center had asked us to repeat our altitude (which had been 10000 ft instead of our 13000 ft clearance altitude). Once on the ground in cos, I called ZDV to try to clarify the situation. I told them exactly what I had done and that I had been distraction by the mode C. They said that the tapes had been pulled and an investigation would follow. My distraction with the transponder resulted in my placing the improper altitude in the altitude selector.

Original NASA ASRS Text

Title: DISTR FLC OF BE02 ERRONEOUSLY DSNDED BELOW ASSIGNED ALT ON ARR TO COS, CO.

Narrative: I WAS CAPT ENRTE FROM ABQ TO COS. FROM OUR ENRTE ALT WE HAD BEEN CLRED TO DSND TO 17000 FT THEN PLT'S DISCRETION TO 13000 FT TO CROSS 35 MI S OF BLACK FOREST VOR AT 13000 FT. OUR ACFT HAD BEEN EXPERIENCING MODE C PROBS WITH OUR XPONDER AND WAS SENDING ERRONEOUS INFO TO ZDV. CTR WAS AWARE OF THE SIT. AT THE TIME OF OUR CLRNC TO DSND, I PRESSED THE TEST BUTTON ON OUR XPONDER AND IT WAS ENCODING APPROX 10000 FT ERRONEOUSLY. I MISTAKENLY PUT 10000 FT IN OUR ALT SELECTOR. WHEN CTR HANDED US OFF TO COS APCH, I RPTED OUR ALT AND WAS ASKED TO REPEAT IT. I REPEATED OUR ALT WITHOUT THINKING ABOUT IT AND ON FINAL TO RWY 35R IN COS I REALIZED WHAT I HAD DONE AND WHY CTR HAD ASKED US TO REPEAT OUR ALT (WHICH HAD BEEN 10000 FT INSTEAD OF OUR 13000 FT CLRNC ALT). ONCE ON THE GND IN COS, I CALLED ZDV TO TRY TO CLARIFY THE SIT. I TOLD THEM EXACTLY WHAT I HAD DONE AND THAT I HAD BEEN DISTR BY THE MODE C. THEY SAID THAT THE TAPES HAD BEEN PULLED AND AN INVESTIGATION WOULD FOLLOW. MY DISTR WITH THE XPONDER RESULTED IN MY PLACING THE IMPROPER ALT IN THE ALT SELECTOR.

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.