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MD90 fails to automatic capture altitude during descent to cvg. Flight crew and approach controller make timely correction.
| Attributes | |
| ACN | 649564 |
| Time | |
| Date | 200503 |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | intersection : obban |
| State Reference | OH |
| Altitude | msl bound lower : 8850 msl bound upper : 9000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : cvg.tracon |
| Operator | common carrier : air carrier |
| Make Model Name | MD-90 Series (DC-9-90) Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent : approach |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 220 flight time total : 7000 flight time type : 3000 |
| ASRS Report | 649564 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : overshoot non adherence : far non adherence : clearance |
| Independent Detector | other controllera other flight crewa |
| Resolutory Action | controller : issued advisory flight crew : returned to assigned altitude |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Aircraft |
Narrative:
We had just crossed obban on the sweed arrival into cvg. We crossed obban at 11000 ft and were either en route to flm or already on a vector; when approach gave us a 'descend and maintain 9000 ft' clearance. As we approached 9000 ft; I noticed the altitude capture did not capture (lost lock) as we were approximately 100-150 ft below 9000 ft and still in a slight descent. The autoplt was disconnected and an immediate climb back to 9000 ft was initiated. The time delay of recognizing the altitude had not captured and making sure the altitude reversal didn't hurt any passenger; our altitude dipped 280 ft below 9000 ft. Approach control questioned our altitude as we had reversed the descent into a climb. There were no traffic conflicts and no one on our TCASII that we could see. We acknowledged that we were climbing back to 9000 ft with cvg approach and the controller didn't seem upset with us. The MD88/90 flight guidance panel does have this glitch at times of not 'capturing' the set altitude. Sometimes it is operator error in that adjusting the 'vertical speed' as the altitude is capturing will cause the loss of altitude capture; but there are times where the 'altitude capture' will lose lock for no reason as it is capturing. I've seen this happen 6 or 7 times in almost 7 yrs on the plane; and just luckily caught the 'loss of altitude captures' in time. We appreciated approach control backing us up as soon as they saw us starting to go through our altitude. Their quick relay to us was great backup and could be invaluable in preventing a conflict.
Original NASA ASRS Text
Title: MD90 FAILS TO AUTO CAPTURE ALT DURING DSCNT TO CVG. FLT CREW AND APCH CTLR MAKE TIMELY CORRECTION.
Narrative: WE HAD JUST CROSSED OBBAN ON THE SWEED ARR INTO CVG. WE CROSSED OBBAN AT 11000 FT AND WERE EITHER ENRTE TO FLM OR ALREADY ON A VECTOR; WHEN APCH GAVE US A 'DSND AND MAINTAIN 9000 FT' CLRNC. AS WE APCHED 9000 FT; I NOTICED THE ALT CAPTURE DID NOT CAPTURE (LOST LOCK) AS WE WERE APPROX 100-150 FT BELOW 9000 FT AND STILL IN A SLIGHT DSCNT. THE AUTOPLT WAS DISCONNECTED AND AN IMMEDIATE CLB BACK TO 9000 FT WAS INITIATED. THE TIME DELAY OF RECOGNIZING THE ALT HAD NOT CAPTURED AND MAKING SURE THE ALT REVERSAL DIDN'T HURT ANY PAX; OUR ALT DIPPED 280 FT BELOW 9000 FT. APCH CTL QUESTIONED OUR ALT AS WE HAD REVERSED THE DSCNT INTO A CLB. THERE WERE NO TFC CONFLICTS AND NO ONE ON OUR TCASII THAT WE COULD SEE. WE ACKNOWLEDGED THAT WE WERE CLBING BACK TO 9000 FT WITH CVG APCH AND THE CTLR DIDN'T SEEM UPSET WITH US. THE MD88/90 FLT GUIDANCE PANEL DOES HAVE THIS GLITCH AT TIMES OF NOT 'CAPTURING' THE SET ALT. SOMETIMES IT IS OPERATOR ERROR IN THAT ADJUSTING THE 'VERT SPD' AS THE ALT IS CAPTURING WILL CAUSE THE LOSS OF ALT CAPTURE; BUT THERE ARE TIMES WHERE THE 'ALT CAPTURE' WILL LOSE LOCK FOR NO REASON AS IT IS CAPTURING. I'VE SEEN THIS HAPPEN 6 OR 7 TIMES IN ALMOST 7 YRS ON THE PLANE; AND JUST LUCKILY CAUGHT THE 'LOSS OF ALT CAPTURES' IN TIME. WE APPRECIATED APCH CTL BACKING US UP AS SOON AS THEY SAW US STARTING TO GO THROUGH OUR ALT. THEIR QUICK RELAY TO US WAS GREAT BACKUP AND COULD BE INVALUABLE IN PREVENTING A CONFLICT.
Data retrieved from NASA's ASRS site as of January 2009 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.