DA2000 first officer describes switching to autopilot #2 at FL430 when air data computer #1 fails. U...

Narrative:

During cruise we encountered a #1 air data computer failure. After reviewing the checklist and talking to company maintenance the captain switched the autopilot over to the #2 air data computer copilot side and then informed me that I had the controls. Unfortunately; during the switch to the #2 side the autopilot reverts to roll and pitch; between the time of the switch and being informed of the transfer of control; the aircraft had climbed over 400 but less then 500 ft above FL430. After noticing the discrepancy; I engaged the heading and pitched back down to FL430. I notified ATC of the discrepancy and that I was returning to the assigned altitude. We never declared an emergency; however we had notified all centers of the abnormality and eventual failure of the air data computer. We checked our altitude readouts against theirs; everything on the #2 side was accurate so I believe that we may have had an altitude deviation. Also; after we did the transfer; we diverted. I notified the center at that time that we were no longer rvsm compliant and that we could start down at any time. We initiated a slow descent thereafter per ATC. The flight finished without any other complications.

Original NASA ASRS Text

Title: DA2000 First Officer describes switching to autopilot #2 at FL430 when ADC #1 fails. Unfortunately the autopilot reverts to pitch and roll when during the switchover and an altitude deviation of 500 FT develops before it is detected. Flight diverts for maintenance.

Narrative: During cruise we encountered a #1 ADC failure. After reviewing the checklist and talking to company maintenance the Captain switched the autopilot over to the #2 ADC Copilot side and THEN informed me that I had the controls. Unfortunately; during the switch to the #2 side the autopilot reverts to roll and pitch; between the time of the switch and being informed of the transfer of control; the aircraft had climbed over 400 but less then 500 FT above FL430. After noticing the discrepancy; I engaged the heading and pitched back down to FL430. I notified ATC of the discrepancy and that I was returning to the assigned altitude. We never declared an emergency; however we had notified all centers of the abnormality and eventual failure of the ADC. We checked our altitude readouts against theirs; everything on the #2 side was accurate so I believe that we may have had an altitude deviation. Also; after we did the transfer; we diverted. I notified the Center at that time that we were no longer RVSM compliant and that we could start down at any time. We initiated a slow descent thereafter per ATC. The flight finished without any other complications.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	945603
Time
Date	201104
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Falcon 2000
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Air Data Computer
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 120 Flight Crew Total 9800 Flight Crew Type 2000
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance

DA2000 first officer describes switching to autopilot #2 at FL430 when air data computer #1 fails. Unfortunately the autopilot reverts to pitch and roll when during the switchover and an altitude deviation of 500 ft develops before it is detected. Flight diverts for maintenance.