Air carrier medium large transport altitude deviation excursion from clearance atl.

Attributes
ACN	185755
Time
Date	199108
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : tys
State Reference	TN
Altitude	msl bound lower : 31000 msl bound upper : 31300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute airway : j22 ztl
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 240 flight time total : 11000 flight time type : 1700
ASRS Report	185755
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

In cruise for less than 30 mins. In 'altitude hold' when autoplt went to 'vertical speed' mode and started climbing. My altimeter showed 31200. (My 250 ft advisory light did not come on!) center immediately said he was reading 31300. The medium large transport FMS has a bad habit of doing this! It has happened numerous times before but was able to catch it. The company has published warnings about it also.

Original NASA ASRS Text

Title: ACR MLG ALT DEV EXCURSION FROM CLRNC ATL.

Narrative: IN CRUISE FOR LESS THAN 30 MINS. IN 'ALT HOLD' WHEN AUTOPLT WENT TO 'VERT SPD' MODE AND STARTED CLBING. MY ALTIMETER SHOWED 31200. (MY 250 FT ADVISORY LIGHT DID NOT COME ON!) CENTER IMMEDIATELY SAID HE WAS READING 31300. THE MLG FMS HAS A BAD HABIT OF DOING THIS! IT HAS HAPPENED NUMEROUS TIMES BEFORE BUT WAS ABLE TO CATCH IT. THE COMPANY HAS PUBLISHED WARNINGS ABOUT IT ALSO.

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.