Altitude deviation altitude overshot -- the altitude capture mode of the autoplt malfunctioned and t...

Attributes
ACN	315801
Time
Date	199509
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : lbf
State Reference	NE
Altitude	msl bound lower : 6680 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv artcc : zdc
Operator	general aviation : personal
Make Model Name	PA-60 600 Aerostar
Operating Under FAR Part	Part 91
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 50 flight time total : 2900 flight time type : 230
ASRS Report	315801
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude altitude deviation : overshoot conflict : airborne less severe non adherence : clearance non adherence : far non adherence : required legal separation
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : took evasive action flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 15000 vertical : 780
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

IFR from ikk to bff, I decided a fuel stop was in order and selected north platte, northeast, lbf. On descent from 12000 ft to 7000 ft I inadvertently descended through my assigned altitude, 7000 ft by 320 ft. This caused a conflict on ZDV radar because of separation of less than 1000 ft. I immediately recognized the error and went back to 7000 ft. The event was only a few seconds in length. During this, the controller asked my altitude and I said that I was low and was correcting. He gave me a number to call when I landed which I did. My aircraft, a PA60 is equipped with KFC200 with altitude preselect. I had taken it off altitude hold, selected 7000 ft and armed the system. At 7000 ft the preselect failed to arrest the descent as expected. I immediately interrupted the system and hand flew the aircraft back to 7000 ft. It took the 320 ft to arrest the descent and correct it. My aircraft was fresh out of the avionics shop just 3 days before this trip. Repairs were made to the autoplt and preselect system. Apparently some malfunction still exists which I will have repaired as soon as I return home. Until that time I will hand fly the climb and descent modes so this problem won't be repeated. In the future, I will never rely on the pre-select equipment to function properly. This whole thing is embarrassing for me as I consider myself to be a good pilot with over 2900 hours. I file IFR even in good VFR WX as it was this day for the added margin of safety IFR offers. I believe in the system. I regret having had to make that phone call to center but I will be a better pilot because this happened, this I am sure of. The controller stated that he saw a descent to 6500 ft. This did not coincide with my altimeter because I arrested the descent at 6680 MSL and climbed back to 7000 ft MSL immediately. As for aircraft #2, he was at 6000 ft and a few mi behind me at my 7 O'clock position. The other aircraft involved in this altitude conflict had reported my aircraft in sight.

Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT -- THE ALT CAPTURE MODE OF THE AUTOPLT MALFUNCTIONED AND THE ACFT DSNDED BELOW ITS ASSIGNED ALT.

Narrative: IFR FROM IKK TO BFF, I DECIDED A FUEL STOP WAS IN ORDER AND SELECTED N PLATTE, NE, LBF. ON DSCNT FROM 12000 FT TO 7000 FT I INADVERTENTLY DSNDED THROUGH MY ASSIGNED ALT, 7000 FT BY 320 FT. THIS CAUSED A CONFLICT ON ZDV RADAR BECAUSE OF SEPARATION OF LESS THAN 1000 FT. I IMMEDIATELY RECOGNIZED THE ERROR AND WENT BACK TO 7000 FT. THE EVENT WAS ONLY A FEW SECONDS IN LENGTH. DURING THIS, THE CTLR ASKED MY ALT AND I SAID THAT I WAS LOW AND WAS CORRECTING. HE GAVE ME A NUMBER TO CALL WHEN I LANDED WHICH I DID. MY ACFT, A PA60 IS EQUIPPED WITH KFC200 WITH ALT PRESELECT. I HAD TAKEN IT OFF ALT HOLD, SELECTED 7000 FT AND ARMED THE SYS. AT 7000 FT THE PRESELECT FAILED TO ARREST THE DSCNT AS EXPECTED. I IMMEDIATELY INTERRUPTED THE SYS AND HAND FLEW THE ACFT BACK TO 7000 FT. IT TOOK THE 320 FT TO ARREST THE DSCNT AND CORRECT IT. MY ACFT WAS FRESH OUT OF THE AVIONICS SHOP JUST 3 DAYS BEFORE THIS TRIP. REPAIRS WERE MADE TO THE AUTOPLT AND PRESELECT SYS. APPARENTLY SOME MALFUNCTION STILL EXISTS WHICH I WILL HAVE REPAIRED AS SOON AS I RETURN HOME. UNTIL THAT TIME I WILL HAND FLY THE CLB AND DSCNT MODES SO THIS PROB WON'T BE REPEATED. IN THE FUTURE, I WILL NEVER RELY ON THE PRE-SELECT EQUIP TO FUNCTION PROPERLY. THIS WHOLE THING IS EMBARRASSING FOR ME AS I CONSIDER MYSELF TO BE A GOOD PLT WITH OVER 2900 HRS. I FILE IFR EVEN IN GOOD VFR WX AS IT WAS THIS DAY FOR THE ADDED MARGIN OF SAFETY IFR OFFERS. I BELIEVE IN THE SYS. I REGRET HAVING HAD TO MAKE THAT PHONE CALL TO CTR BUT I WILL BE A BETTER PLT BECAUSE THIS HAPPENED, THIS I AM SURE OF. THE CTLR STATED THAT HE SAW A DSCNT TO 6500 FT. THIS DID NOT COINCIDE WITH MY ALTIMETER BECAUSE I ARRESTED THE DSCNT AT 6680 MSL AND CLBED BACK TO 7000 FT MSL IMMEDIATELY. AS FOR ACFT #2, HE WAS AT 6000 FT AND A FEW MI BEHIND ME AT MY 7 O'CLOCK POS. THE OTHER ACFT INVOLVED IN THIS ALT CONFLICT HAD RPTED MY ACFT IN SIGHT.

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.

Altitude deviation altitude overshot -- the altitude capture mode of the autoplt malfunctioned and the aircraft descended below its assigned altitude.