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An aero commander 685 pilot descended out of rvsm airspace and diverted for maintenance when a recently installed adahrs computer appeared to fail.
| Attributes | |
| ACN | 984230 |
| Time | |
| Date | 201111 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZOB.ARTCC |
| State Reference | OH |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | Aero Commander 695 |
| Operating Under FAR Part | Part 91 |
| Flight Phase | Cruise |
| Route In Use | Direct |
| Flight Plan | IFR |
| Person 1 | |
| Function | Pilot Flying Single Pilot |
| Qualification | Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP) Flight Crew Glider Flight Crew Multiengine Flight Crew Instrument |
| Experience | Flight Crew Last 90 Days 50 Flight Crew Total 23000 Flight Crew Type 300 |
| Events | |
| Anomaly | ATC Issue All Types Aircraft Equipment Problem Less Severe |
Narrative:
The aircraft had just completed an rvsm inspection at a maintenance facility. The adahrs [air data attitude and heading reference system] computer had failed the test and was replaced with another which also failed. A third computer was installed and the aircraft then passed and completed the maintenance inspection. I then departed on a ferry flight to pick up passengers. While in cruise flight at FL330 I felt the airplane lurch. The captain's pfd airspeed was well above redline and the altimeter read 37;000. The autopilot had begun a rapid descent. Comparing the standby; captain's and copilot's instruments I determined the captain's instruments and autopilot actions were erroneous; disconnected the autopilot and began a climb from FL323 back up to FL330. While doing so I notified ATC I had a computer failure; was no longer rvsm capable and required a lower altitude. I was assigned and descended to FL250 where all indications returned to normal. When I had stabilized and assessed the situation I determined a deviation to our home base was the best course of action and ATC cleared me direct. The flight was completed without further incident. From the problems that occurred we believe the third installed adahrs computer also malfunctioned.
Original NASA ASRS Text
Title: An Aero Commander 685 pilot descended out of RVSM airspace and diverted for maintenance when a recently installed ADAHRS computer appeared to fail.
Narrative: The aircraft had just completed an RVSM inspection at a maintenance facility. The ADAHRS [Air Data Attitude and Heading Reference System] computer had failed the test and was replaced with another which also failed. A third computer was installed and the aircraft then passed and completed the maintenance inspection. I then departed on a ferry flight to pick up passengers. While in cruise flight at FL330 I felt the airplane lurch. The Captain's PFD airspeed was well above redline and the altimeter read 37;000. The autopilot had begun a rapid descent. Comparing the standby; Captain's and copilot's instruments I determined the Captain's instruments and autopilot actions were erroneous; disconnected the autopilot and began a climb from FL323 back up to FL330. While doing so I notified ATC I had a computer failure; was no longer RVSM capable and required a lower altitude. I was assigned and descended to FL250 where all indications returned to normal. When I had stabilized and assessed the situation I determined a deviation to our home base was the best course of action and ATC cleared me direct. The flight was completed without further incident. From the problems that occurred we believe the third installed ADAHRS computer also malfunctioned.
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.