Narrative:

During a routine night flight, our primary ADI and gyro failed. Initial indications were abnormal bank of 10 degrees or more followed by a gradual increase in bank and pitch indications. Autoplt functions were also abnormal as indicators depicted normal roll and pitch engagement, but was actually disabled due to vertical gyro failure. After several attempts of re-engagement, autoplt was rendered useless. While distraction with primary attitude gyro indications and autoplt failure, the PF was disoriented and attempted to recover from an unusual attitude as depicted on the primary ADI. Even though visual aids to outside horizon and 2 supporting back-up attitude indicators revealed a normal straight and level cruise confign, an attempt was made to recover to normal. Approximately 500 ft was lost and 40 degrees left deviation off course. ZTL was immediately notified as to the nature of the problem, ie, gyro failure, and deviation recovery, ie, returning to normal on course and altitude assignments. The PNF announced his action to take the controls from the PF and immediately initiated a recovery to normal straight and level cruise confign. Once aircraft was re-established on course, controls were returned to the original PF, after the primary ADI was covered and completely out of primary instrument scan. This whole event could have been prevented if the primary ADI had been covered up earlier and/or controls relinquished to the first officer with normal flight instruments until aircraft troubleshooting had been accomplished.

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Original NASA ASRS Text

Title: LR55 DEVIATES FROM ASSIGNED ALT AFTER EXPERIENCING ADI FAILURE IN ATL AIRSPACE.

Narrative: DURING A ROUTINE NIGHT FLT, OUR PRIMARY ADI AND GYRO FAILED. INITIAL INDICATIONS WERE ABNORMAL BANK OF 10 DEGS OR MORE FOLLOWED BY A GRADUAL INCREASE IN BANK AND PITCH INDICATIONS. AUTOPLT FUNCTIONS WERE ALSO ABNORMAL AS INDICATORS DEPICTED NORMAL ROLL AND PITCH ENGAGEMENT, BUT WAS ACTUALLY DISABLED DUE TO VERT GYRO FAILURE. AFTER SEVERAL ATTEMPTS OF RE-ENGAGEMENT, AUTOPLT WAS RENDERED USELESS. WHILE DISTR WITH PRIMARY ATTITUDE GYRO INDICATIONS AND AUTOPLT FAILURE, THE PF WAS DISORIENTED AND ATTEMPTED TO RECOVER FROM AN UNUSUAL ATTITUDE AS DEPICTED ON THE PRIMARY ADI. EVEN THOUGH VISUAL AIDS TO OUTSIDE HORIZON AND 2 SUPPORTING BACK-UP ATTITUDE INDICATORS REVEALED A NORMAL STRAIGHT AND LEVEL CRUISE CONFIGN, AN ATTEMPT WAS MADE TO RECOVER TO NORMAL. APPROX 500 FT WAS LOST AND 40 DEGS L DEV OFF COURSE. ZTL WAS IMMEDIATELY NOTIFIED AS TO THE NATURE OF THE PROB, IE, GYRO FAILURE, AND DEV RECOVERY, IE, RETURNING TO NORMAL ON COURSE AND ALT ASSIGNMENTS. THE PNF ANNOUNCED HIS ACTION TO TAKE THE CTLS FROM THE PF AND IMMEDIATELY INITIATED A RECOVERY TO NORMAL STRAIGHT AND LEVEL CRUISE CONFIGN. ONCE ACFT WAS RE-ESTABLISHED ON COURSE, CTLS WERE RETURNED TO THE ORIGINAL PF, AFTER THE PRIMARY ADI WAS COVERED AND COMPLETELY OUT OF PRIMARY INST SCAN. THIS WHOLE EVENT COULD HAVE BEEN PREVENTED IF THE PRIMARY ADI HAD BEEN COVERED UP EARLIER AND/OR CTLS RELINQUISHED TO THE FO WITH NORMAL FLT INSTS UNTIL ACFT TROUBLESHOOTING HAD BEEN ACCOMPLISHED.

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.