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Altitude deviation altitude excursion when aircraft autoplt altitude hold fails. Aircraft starts descent to occupied altitude. Near midair collision.
| Attributes | |
| ACN | 361650 |
| Time | |
| Date | 199702 |
| Day | Sun |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : pxr |
| State Reference | AZ |
| Altitude | msl bound lower : 15700 msl bound upper : 16000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zab |
| Operator | general aviation : personal |
| Make Model Name | Any Unknown or Unlisted Aircraft Manufacturer |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise other descent other |
| Route In Use | enroute other |
| Flight Plan | IFR |
| Aircraft 2 | |
| Make Model Name | King Air 100 A/B |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise other descent other |
| Route In Use | enroute other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | Other |
| Function | flight crew : single pilot |
| Qualification | other other : other pilot : commercial |
| Experience | flight time last 90 days : 57 flight time total : 814 flight time type : 218 |
| ASRS Report | 361650 |
| Person 2 | |
| Affiliation | Other |
| Function | flight crew : single pilot |
| Qualification | pilot : commercial pilot : instrument |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude conflict : nmac non adherence : clearance |
| Independent Detector | other controllera other flight crewa |
| Resolutory Action | flight crew : took evasive action flight crew : returned to intended course or assigned course other |
| Consequence | Other |
| Miss Distance | vertical : 400 |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation other |
Narrative:
On a IFR flight plan from gjt and sdl, I was cleared to descend from FL200 to 16000 ft. Upon descent through 16500 ft I called center, asking for 14000 ft. They denied the request stating I had traffic, a king air at 2 O'clock at 15000 ft. As soon as they started him down they would give me lower. I looked for and reported having the traffic in sight. My aircraft was on the autoplt with the altitude preselect set to 16000 ft. I heard the audible as it approached 16000 ft and felt the aircraft begin to level off. I saw the altitude capture light up on the altitude preselect. Approximately 1-2 mins later as I scanned through the gauges. I noticed a gradual descent and the altimeter showed 15700 ft. I disconnected the autoplt and began a climb back to 16000 ft. As I started my climb, ZAB called to verify my altitude. I responded that I was climbing back to 16000 ft and the autoplt had dropped the altitude hold. After reaching 16000 ft abq called, clearing me to descend to 11000 ft, 'if I had the king air in sight at 11 O'clock position.' I responded and began a descent to 11000 ft using the autoplt again. Upon reaching 11000 ft the autoplt behaved the same as it had at 16000 ft. I then turned the autoplt off and hand flew the aircraft, marking the autoplt inoperative. The aircraft is currently in maintenance having the autoplt diagnosed.
Original NASA ASRS Text
Title: ALTDEV ALT EXCURSION WHEN ACFT AUTOPLT ALT HOLD FAILS. ACFT STARTS DSCNT TO OCCUPIED ALT. NMAC.
Narrative: ON A IFR FLT PLAN FROM GJT AND SDL, I WAS CLRED TO DSND FROM FL200 TO 16000 FT. UPON DSCNT THROUGH 16500 FT I CALLED CTR, ASKING FOR 14000 FT. THEY DENIED THE REQUEST STATING I HAD TFC, A KING AIR AT 2 O'CLOCK AT 15000 FT. AS SOON AS THEY STARTED HIM DOWN THEY WOULD GIVE ME LOWER. I LOOKED FOR AND RPTED HAVING THE TFC IN SIGHT. MY ACFT WAS ON THE AUTOPLT WITH THE ALT PRESELECT SET TO 16000 FT. I HEARD THE AUDIBLE AS IT APCHED 16000 FT AND FELT THE ACFT BEGIN TO LEVEL OFF. I SAW THE ALT CAPTURE LIGHT UP ON THE ALT PRESELECT. APPROX 1-2 MINS LATER AS I SCANNED THROUGH THE GAUGES. I NOTICED A GRADUAL DSCNT AND THE ALTIMETER SHOWED 15700 FT. I DISCONNECTED THE AUTOPLT AND BEGAN A CLB BACK TO 16000 FT. AS I STARTED MY CLB, ZAB CALLED TO VERIFY MY ALT. I RESPONDED THAT I WAS CLBING BACK TO 16000 FT AND THE AUTOPLT HAD DROPPED THE ALT HOLD. AFTER REACHING 16000 FT ABQ CALLED, CLRING ME TO DSND TO 11000 FT, 'IF I HAD THE KING AIR IN SIGHT AT 11 O'CLOCK POS.' I RESPONDED AND BEGAN A DSCNT TO 11000 FT USING THE AUTOPLT AGAIN. UPON REACHING 11000 FT THE AUTOPLT BEHAVED THE SAME AS IT HAD AT 16000 FT. I THEN TURNED THE AUTOPLT OFF AND HAND FLEW THE ACFT, MARKING THE AUTOPLT INOP. THE ACFT IS CURRENTLY IN MAINT HAVING THE AUTOPLT DIAGNOSED.
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.