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An MD11 first officer, PF, reported that the captain was troubleshooting a failed CADC #2, and momentarily caused a false altitude reading, setting off the TCASII and prompting ATC to call.
| Attributes | |
| ACN | 454040 |
| Time | |
| Date | 199911 |
| Day | Thu |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| State Reference | TN |
| Altitude | msl single value : 27000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : ztl.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | MD-11 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Phase | cruise : level |
| Route In Use | enroute : direct |
| Flight Plan | IFR |
| Aircraft 2 | |
| Controlling Facilities | artcc : ztl.artcc |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : multi engine pilot : instrument pilot : flight engineer pilot : commercial pilot : atp |
| Experience | flight time last 90 days : 100 flight time total : 8000 flight time type : 1280 |
| ASRS Report | 454040 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | aircraft equipment problem : less severe conflict : airborne less severe other anomaly other |
| Independent Detector | aircraft equipment : tcas other controllera |
| Resolutory Action | controller : issued advisory flight crew : returned to assigned altitude |
| Consequence | other |
| Miss Distance | horizontal : 15000 vertical : 1000 |
| Supplementary | |
| Problem Areas | Aircraft |
| Primary Problem | Aircraft |
Narrative:
First officer flying and talking to ATC while captain talked to maintenance coordinator to troubleshoot failed CADC (central air data computer) #2. Autoplt on, level FL270. At maintenance coordinator's suggestion, first officer switched back to failed CADC which gave us an inaccurate altitude readout of FL273 which resulted in a TA to descend and a call from ATC saying we were 300 ft high. We descended to be safe. We then switched back to CADC #1 and the first officer altitude went from FL270 to FL267. We then climbed back to FL270. We then returned to atl because of equipment failure.
Original NASA ASRS Text
Title: AN MD11 FO, PF, RPTED THAT THE CAPT WAS TROUBLESHOOTING A FAILED CADC #2, AND MOMENTARILY CAUSED A FALSE ALT READING, SETTING OFF THE TCASII AND PROMPTING ATC TO CALL.
Narrative: FO FLYING AND TALKING TO ATC WHILE CAPT TALKED TO MAINT COORDINATOR TO TROUBLESHOOT FAILED CADC (CENTRAL AIR DATA COMPUTER) #2. AUTOPLT ON, LEVEL FL270. AT MAINT COORDINATOR'S SUGGESTION, FO SWITCHED BACK TO FAILED CADC WHICH GAVE US AN INACCURATE ALT READOUT OF FL273 WHICH RESULTED IN A TA TO DSND AND A CALL FROM ATC SAYING WE WERE 300 FT HIGH. WE DSNDED TO BE SAFE. WE THEN SWITCHED BACK TO CADC #1 AND THE FO ALT WENT FROM FL270 TO FL267. WE THEN CLBED BACK TO FL270. WE THEN RETURNED TO ATL BECAUSE OF EQUIP FAILURE.
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.