Altitude deviation. Excursion from assigned altitude.

Attributes
ACN	147872
Time
Date	199006
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : drk
State Reference	AZ
Altitude	msl bound lower : 31000 msl bound upper : 31300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zab
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 1000
ASRS Report	147872
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time total : 17000
ASRS Report	148343
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

The aircraft was in cruise at FL310 with perf engaged (medium large transport aircraft). We had just made a 30 degree heading change on the arwy en route to lax. After intercepting the outbnd radial both the captain and I opened our charts to prepare for the arrival to lax when the altitude alert warning indicated a deviation. The altitude was approximately FL313. Perf was disengaged, the flight guidance panel used to recapture altitude. Cause: perf failed to hold altitude. There had been no previous indications of problems with the perf system. The remainder of the flight was uneventful. Supplemental information from acn 148343: when perf disconnects, there is no aural alert until its too late and the assigned altitude is exceeded. The only indication of perf disconnecting is a momentary flashing in the flight mode annunciator, and then annunciating a flight mode other than perf and not in an altitude hold mode.

Original NASA ASRS Text

Title: ALT DEVIATION. EXCURSION FROM ASSIGNED ALT.

Narrative: THE ACFT WAS IN CRUISE AT FL310 WITH PERF ENGAGED (MLG ACFT). WE HAD JUST MADE A 30 DEG HDG CHANGE ON THE ARWY ENRTE TO LAX. AFTER INTERCEPTING THE OUTBND RADIAL BOTH THE CAPT AND I OPENED OUR CHARTS TO PREPARE FOR THE ARR TO LAX WHEN THE ALT ALERT WARNING INDICATED A DEV. THE ALT WAS APPROX FL313. PERF WAS DISENGAGED, THE FLT GUIDANCE PANEL USED TO RECAPTURE ALT. CAUSE: PERF FAILED TO HOLD ALT. THERE HAD BEEN NO PREVIOUS INDICATIONS OF PROBS WITH THE PERF SYS. THE REMAINDER OF THE FLT WAS UNEVENTFUL. SUPPLEMENTAL INFO FROM ACN 148343: WHEN PERF DISCONNECTS, THERE IS NO AURAL ALERT UNTIL ITS TOO LATE AND THE ASSIGNED ALT IS EXCEEDED. THE ONLY INDICATION OF PERF DISCONNECTING IS A MOMENTARY FLASHING IN THE FLT MODE ANNUNCIATOR, AND THEN ANNUNCIATING A FLT MODE OTHER THAN PERF AND NOT IN AN ALT HOLD MODE.

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.