After initiating an autopilot descent; a cessna citation 10 (ce-750) flight crew suddenly experience...

Attributes
ACN	763887
Time
Date	200711
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 24000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	Citation X
Operating Under FAR Part	Part 91
Flight Phase	climbout other
Route In Use	arrival star : n/a
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : atp pilot : cfi pilot : multi engine
Experience	flight time last 90 days : 120 flight time total : 4000 flight time type : 350
ASRS Report	763887
Person 2
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Events
Anomaly	aircraft equipment problem : critical altitude deviation : overshoot other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to original clearance flight crew : overcame equipment problem flight crew : exited penetrated airspace flight crew : regained aircraft control other
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

While on the abc arrival into ZZZ; we had just been given instructions to cross xxxxx intersection at and maintain 13000 ft. The captain set 13000 ft in the altitude selector and I confirmed it. I then selected vertical speed on the flight guidance computer; commanded a 1400 FPM descent rate and visually confirmed both the vertical speed command box and the command bug; showing a descent. Additionally; I observed the aircraft initiated a descent. We then looked down at the arrival to confirm the clearance we just received matched the arrival. Suddenly we felt ourselves sinking into our seat and realized we were in a rapid climb. We looked up to see a climb in excess of 3000 FPM. At approximately FL245; I disconnected the autoplt and initiated a descent. At approximately FL249; the climb was stopped and we then started a descent. We received a query from center as we were passing through FL235 requesting confirmation we were descending to 13000 ft. The captain replied 'we are out of FL235 descending to 13000 ft.' we were given a phone number to call center. The captain called soon after we landed and was told by the individual at center that he replayed the event and saw the aircraft initially start a descent; then climb to FL249. According to him; this set off warnings and that the event caught them off-guard. He said that we never lost the required separation from another aircraft near us; but rather he was very curious as to what had happened. The captain wrote up the aircraft for the uncommanded climb. The avionics mechanic found 2 faults in the air data computer related to invalid vertical guidance data. What I learned from this experience is that you can never fully trust a flight guidance computer/autoplt to do what has been commanded. Since a fault can occur at any time you must always be vigilant in monitoring its progress especially during transitions.

Original NASA ASRS Text

Title: AFTER INITIATING AN AUTOPILOT DESCENT; A CESSNA CITATION 10 (CE-750) FLIGHT CREW SUDDENLY EXPERIENCED AN UNCOMMANDED RAPID CLIMB IN EXCESS OF 3000 FPM; REQUIRING CAPTAIN TO DISCONNECT THE AUTOPILOT TO REGAIN CONTROL.

Narrative: WHILE ON THE ABC ARR INTO ZZZ; WE HAD JUST BEEN GIVEN INSTRUCTIONS TO CROSS XXXXX INTXN AT AND MAINTAIN 13000 FT. THE CAPT SET 13000 FT IN THE ALT SELECTOR AND I CONFIRMED IT. I THEN SELECTED VERT SPD ON THE FLT GUIDANCE COMPUTER; COMMANDED A 1400 FPM DSCNT RATE AND VISUALLY CONFIRMED BOTH THE VERT SPD COMMAND BOX AND THE COMMAND BUG; SHOWING A DSCNT. ADDITIONALLY; I OBSERVED THE ACFT INITIATED A DSCNT. WE THEN LOOKED DOWN AT THE ARR TO CONFIRM THE CLRNC WE JUST RECEIVED MATCHED THE ARR. SUDDENLY WE FELT OURSELVES SINKING INTO OUR SEAT AND REALIZED WE WERE IN A RAPID CLB. WE LOOKED UP TO SEE A CLB IN EXCESS OF 3000 FPM. AT APPROX FL245; I DISCONNECTED THE AUTOPLT AND INITIATED A DSCNT. AT APPROX FL249; THE CLB WAS STOPPED AND WE THEN STARTED A DSCNT. WE RECEIVED A QUERY FROM CTR AS WE WERE PASSING THROUGH FL235 REQUESTING CONFIRMATION WE WERE DSNDING TO 13000 FT. THE CAPT REPLIED 'WE ARE OUT OF FL235 DSNDING TO 13000 FT.' WE WERE GIVEN A PHONE NUMBER TO CALL CTR. THE CAPT CALLED SOON AFTER WE LANDED AND WAS TOLD BY THE INDIVIDUAL AT CTR THAT HE REPLAYED THE EVENT AND SAW THE ACFT INITIALLY START A DSCNT; THEN CLB TO FL249. ACCORDING TO HIM; THIS SET OFF WARNINGS AND THAT THE EVENT CAUGHT THEM OFF-GUARD. HE SAID THAT WE NEVER LOST THE REQUIRED SEPARATION FROM ANOTHER ACFT NEAR US; BUT RATHER HE WAS VERY CURIOUS AS TO WHAT HAD HAPPENED. THE CAPT WROTE UP THE ACFT FOR THE UNCOMMANDED CLB. THE AVIONICS MECH FOUND 2 FAULTS IN THE AIR DATA COMPUTER RELATED TO INVALID VERT GUIDANCE DATA. WHAT I LEARNED FROM THIS EXPERIENCE IS THAT YOU CAN NEVER FULLY TRUST A FLT GUIDANCE COMPUTER/AUTOPLT TO DO WHAT HAS BEEN COMMANDED. SINCE A FAULT CAN OCCUR AT ANY TIME YOU MUST ALWAYS BE VIGILANT IN MONITORING ITS PROGRESS ESPECIALLY DURING TRANSITIONS.

Data retrieved from NASA's ASRS site as of January 2009 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.

After initiating an autopilot descent; a cessna citation 10 (ce-750) flight crew suddenly experienced an uncommanded rapid climb in excess of 3000 FPM; requiring captain to disconnect the autopilot to regain control.