|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||1801 To 2400|
|Locale Reference||atc facility : das|
|Altitude||msl bound lower : 9700|
msl bound upper : 10000
|Controlling Facilities||artcc : zhu|
|Operator||common carrier : air carrier|
|Make Model Name||Medium Large Transport, Low Wing, 2 Turbojet Eng|
|Navigation In Use||Other|
|Flight Phase||descent other|
|Route In Use||arrival star : star|
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Qualification||pilot : flight engineer|
pilot : atp
|Experience||flight time last 90 days : 125|
flight time total : 8940
flight time type : 495
|Anomaly||aircraft equipment problem : less severe|
altitude deviation : overshoot
|Independent Detector||other flight crewa|
|Resolutory Action||flight crew : returned to intended course or assigned course|
|Air Traffic Incident||Pilot Deviation|
Altimeters set correctly to local setting. Descending to 10000' MSL at 250 KIAS. Aircraft is medium large transport. Altitude is armed at 10000', speed select at 250 KTS. When aircraft is about to level at 10000' MSL flight guidance suddenly goes into vertical speed at about 2100' descended. I immediately pressed altitude hold 2 or 3 times, but had no effect. Disconnected autoplt and manually flew back to 10000' MSL. Altitude deviation was 250-300' down from 10000'. Altitude voice from CAWS was heard and also altitude light on altimeter illuminated. Reason for excursion unknown. Flight guidance system just had a mind of its own. Pilot was not touching anything when excursion started. System was set properly and altitude armed.
Original NASA ASRS Text
Title: ACR MLG OVERSHOT ALT DESCENT DUE TO AUTOPLT MALFUNCTION.
Narrative: ALTIMETERS SET CORRECTLY TO LCL SETTING. DSNDING TO 10000' MSL AT 250 KIAS. ACFT IS MLG. ALT IS ARMED AT 10000', SPD SELECT AT 250 KTS. WHEN ACFT IS ABOUT TO LEVEL AT 10000' MSL FLT GUIDANCE SUDDENLY GOES INTO VERT SPD AT ABOUT 2100' DESCENDED. I IMMEDIATELY PRESSED ALT HOLD 2 OR 3 TIMES, BUT HAD NO EFFECT. DISCONNECTED AUTOPLT AND MANUALLY FLEW BACK TO 10000' MSL. ALT DEVIATION WAS 250-300' DOWN FROM 10000'. ALT VOICE FROM CAWS WAS HEARD AND ALSO ALT LIGHT ON ALTIMETER ILLUMINATED. REASON FOR EXCURSION UNKNOWN. FLT GUIDANCE SYS JUST HAD A MIND OF ITS OWN. PLT WAS NOT TOUCHING ANYTHING WHEN EXCURSION STARTED. SYS WAS SET PROPERLY AND ALT ARMED.
Data retrieved from NASA's ASRS site as of August 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.