A CE560XL received a heading failure on the pilot's pfd followed by an altitude failure alert when t...

Attributes
ACN	976042
Time
Date	201110
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Citation Excel (C560XL)
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	Air Data Computer
Person 1
Function	Captain
Qualification	Flight Crew Flight Instructor Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 100 Flight Crew Total 14000 Flight Crew Type 850
Events
Anomaly	ATC Issue All Types Aircraft Equipment Problem Critical Deviation - Altitude Overshoot Deviation - Procedural Clearance

Narrative:

On a deadhead flight we were assigned a descent to 3;000. During the descent a new altitude of 4;000 was given. We received this altitude approximately 4;400-4;300 ft. As we started to level a heading failure popped up on pilots pfd; during transfer a second failure appeared; altitude failure followed by a pfd failure. During the descent the autopilot was engaged but failed to level at 4;000. Being IFR with several failures altitude was not noticed for several seconds. We descended to approximately 3;400-3;500 ft. We climbed back to 4;000 within a few seconds. As soon as we leveled ATC gave us 2;000 ft. No comment on altitude loss from ATC. Several factors played into this equipment failure plus my slow decision to hand off flying to the copilot. What started out as a simple problem soon turned into a very big one. We have reviewed every step of this flight. Also; CRM was reviewed and discussed by all crew members.

Original NASA ASRS Text

Title: A CE560XL received a HDG FAILURE on the pilot's PFD followed by an ALT FAILURE alert when the Air Data Computer failed. An altitude deviation occurred before the First Officer began flying.

Narrative: On a deadhead flight we were assigned a descent to 3;000. During the descent a new altitude of 4;000 was given. We received this altitude approximately 4;400-4;300 FT. As we started to level a HDG FAILURE popped up on pilots PFD; during transfer a second failure appeared; ALT FAILURE followed by a PFD failure. During the descent the autopilot was engaged but failed to level at 4;000. Being IFR with several failures ALT was not noticed for several seconds. We descended to approximately 3;400-3;500 FT. We climbed back to 4;000 within a few seconds. As soon as we leveled ATC gave us 2;000 FT. No comment on ALT loss from ATC. Several factors played into this equipment failure plus my slow decision to hand off flying to the Copilot. What started out as a simple problem soon turned into a very big one. We have reviewed every step of this flight. Also; CRM was reviewed and discussed by all crew members.

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.

A CE560XL received a heading failure on the pilot's pfd followed by an altitude failure alert when the air data computer failed. An altitude deviation occurred before the first officer began flying.