Aircraft equipment problem, transponder. Flight crew distraction.

Attributes
ACN	307050
Time
Date	199506
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : mbw
State Reference	WY
Altitude	msl bound lower : 24500 msl bound upper : 25000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv tower : sfo
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 135
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 4000 flight time type : 400
ASRS Report	307050
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Cruising at FL250 en route from riw to den. Clearance was direct mbw VOR ramms 1 arrival den. WX was cavu smooth air. About 20 mi from mbw VOR (where the course changed and STAR began), ATC said we were 500 ft low. We verified both altimeters were within 100 ft of FL250 and both altimeters were set to 29.92. We advised ATC we were maintaining FL250. At this time we began to troubleshoot. The transponder(south) have a test mode which shows mode, altitude being sent to ATC, sure enough it was sending back FL245 even though we were maintaining FL250 we tried switching xponders, no help, static heat no help, recycling no help, alternate static. Finally requested descent to FL230 to see if this would help. We had just completed the descent checklist when we noticed we had crossed mbw VOR where we should have turned. We overshot by 8 mi. We began an immediate turn back on course. ATC then advised us we were 10 east off course. We offered our apologies and said we were correcting. There was no terrain or traffic conflict (we were VMC). In 4000 hours of flying I have never done anything like this nor had the captain. Obviously what caused it was preoccupation with the transponder. I am well aware of the problems distrs can lead to. In fact, I used to teach my students not to let minor distrs interfere with task #1, flying the airplane! Perhaps I needed a refresher in that same lesson and today I got it. My advice to fellow pilots, when a problem (distraction) occurs, deal with it and then without delay get back to flying the airplane!

Original NASA ASRS Text

Title: ACFT EQUIP PROB, XPONDER. FLC DISTR.

Narrative: CRUISING AT FL250 ENRTE FROM RIW TO DEN. CLRNC WAS DIRECT MBW VOR RAMMS 1 ARR DEN. WX WAS CAVU SMOOTH AIR. ABOUT 20 MI FROM MBW VOR (WHERE THE COURSE CHANGED AND STAR BEGAN), ATC SAID WE WERE 500 FT LOW. WE VERIFIED BOTH ALTIMETERS WERE WITHIN 100 FT OF FL250 AND BOTH ALTIMETERS WERE SET TO 29.92. WE ADVISED ATC WE WERE MAINTAINING FL250. AT THIS TIME WE BEGAN TO TROUBLESHOOT. THE XPONDER(S) HAVE A TEST MODE WHICH SHOWS MODE, ALT BEING SENT TO ATC, SURE ENOUGH IT WAS SENDING BACK FL245 EVEN THOUGH WE WERE MAINTAINING FL250 WE TRIED SWITCHING XPONDERS, NO HELP, STATIC HEAT NO HELP, RECYCLING NO HELP, ALTERNATE STATIC. FINALLY REQUESTED DSCNT TO FL230 TO SEE IF THIS WOULD HELP. WE HAD JUST COMPLETED THE DSCNT CHKLIST WHEN WE NOTICED WE HAD CROSSED MBW VOR WHERE WE SHOULD HAVE TURNED. WE OVERSHOT BY 8 MI. WE BEGAN AN IMMEDIATE TURN BACK ON COURSE. ATC THEN ADVISED US WE WERE 10 E OFF COURSE. WE OFFERED OUR APOLOGIES AND SAID WE WERE CORRECTING. THERE WAS NO TERRAIN OR TFC CONFLICT (WE WERE VMC). IN 4000 HRS OF FLYING I HAVE NEVER DONE ANYTHING LIKE THIS NOR HAD THE CAPT. OBVIOUSLY WHAT CAUSED IT WAS PREOCCUPATION WITH THE XPONDER. I AM WELL AWARE OF THE PROBS DISTRS CAN LEAD TO. IN FACT, I USED TO TEACH MY STUDENTS NOT TO LET MINOR DISTRS INTERFERE WITH TASK #1, FLYING THE AIRPLANE! PERHAPS I NEEDED A REFRESHER IN THAT SAME LESSON AND TODAY I GOT IT. MY ADVICE TO FELLOW PLTS, WHEN A PROB (DISTR) OCCURS, DEAL WITH IT AND THEN WITHOUT DELAY GET BACK TO FLYING THE AIRPLANE!

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.