A crj-700 flight crew experienced air data computer and ahrs failures in cruise at FL270. A loss of ...

Narrative:

In cruise at FL270 I was manually flying the aircraft when my pfd went blank for a few seconds. The autopilot had been deferred so I tried to hold course and altitude while cross-reading the captain's pfd; which had just come back on after blanking out momentarily as well. When my screen returned it was showing erroneous attitude and navigation information. It was clear that ahrs 2 had failed. At that point I realized I was losing altitude and suggested that the captain take the controls because I didn't know if I was receiving reliable altitude data. I also noticed our vertical speeds were not in agreement. The captain had pulled out the checklist so he could not take the controls. When the altitude alerter came on I began to pitch up more aggressively. Upon reaching our assigned altitude I transferred the controls to the captain and we notified ATC of the deviation. We completed the checklist and continued on. The only undesired state that occurred was the 300-foot loss of altitude due to the distraction described above.in hindsight I should have cross-checked the standby instruments for additional info. Also I should have offered to transfer the controls before the captain pulled out the checklist since I was distracted and struggling to hold altitude. Quicker communication probably could have prevented the deviation.

Original NASA ASRS Text

Title: A CRJ-700 flight crew experienced ADC and AHRS failures in cruise at FL270. A loss of 300 feet of altitude resulted before they regained the necessary instrumentation.

Narrative: In cruise at FL270 I was manually flying the aircraft when my PFD went blank for a few seconds. The autopilot had been deferred so I tried to hold course and altitude while cross-reading the Captain's PFD; which had just come back on after blanking out momentarily as well. When my screen returned it was showing erroneous attitude and navigation information. It was clear that AHRS 2 had failed. At that point I realized I was losing altitude and suggested that the Captain take the controls because I didn't know if I was receiving reliable altitude data. I also noticed our vertical speeds were not in agreement. The Captain had pulled out the checklist so he could not take the controls. When the altitude alerter came on I began to pitch up more aggressively. Upon reaching our assigned altitude I transferred the controls to the Captain and we notified ATC of the deviation. We completed the checklist and continued on. The only undesired state that occurred was the 300-foot loss of altitude due to the distraction described above.In hindsight I should have cross-checked the standby instruments for additional info. Also I should have offered to transfer the controls before the Captain pulled out the checklist since I was distracted and struggling to hold altitude. Quicker communication probably could have prevented the deviation.

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	959280
Time
Date	201107
Local Time Of Day	1201-1800
Place
Locale Reference	ZID.ARTCC
State Reference	IN
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Regional Jet 700 ER/LR (CRJ700)
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	AHRS/ND
Person 1
Function	First Officer Pilot Flying
Person 2
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Altitude Excursion From Assigned Altitude

A crj-700 flight crew experienced air data computer and ahrs failures in cruise at FL270. A loss of 300 feet of altitude resulted before they regained the necessary instrumentation.