Air carrier medium large transport altitude deviation overshot during descent. Flight crew claims th...

Attributes
ACN	158189
Time
Date	199009
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : fim
State Reference	CA
Altitude	msl bound lower : 23000 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
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 descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 25 flight time total : 12000 flight time type : 200
ASRS Report	158189
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Inbound to fillmore VOR from the east with autoflt engaged, aircraft was descending from 35000' with intermediate level-offs, for a planned landing at sba. In level flight at 28000' aircraft was cleared to maintain 24000'. Clearance was acknowledged and new altitude set in MCP altitude set window and checked by both pilots. Level change was selected on MCP (an autoplt descent mode) and aircraft started down at approximately 3000 FPM. At approximately 26000' PNF checked off (with PF concurrence) from monitoring ATC to listen to sba ATIS. Time off ATC frequency approximately 1 min. At approximately 24000' PF received frequency change from ZLA and when checking in with new controller, reported passing approximately 23000 for 21000'--21000' being the altitude showing in the MCP altitude window, however not set by either pilot. Controller acknowledged transmission then requested last altitude clearance. PF once again responded 'FL210,' because that was the altitude set in MCP altitude window. Controller acknowledged transmission and subsequently cleared aircraft to maintain FL220. Problem area: PNF out of loop for approximately 1 min while obtaining ATIS which was worth 3000' of altitude los. PF accepted altitude set in MCP window as correct altitude from last clearance. Uncommanded altitude change in electronic altitude set window due software problem? Corrective action: greater diligence on part of pilots, especially when only one is flying and communicating. Uncommanded altitude change is recurring problem in glass cockpit--need change in software of install a more traditional altitude set window.

Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT. FLT CREW CLAIMS THEY SET 240 IN ALT ALERT, BUT APPROX 1 MINUTE LATER IT READ 210.

Narrative: INBND TO FILLMORE VOR FROM THE E WITH AUTOFLT ENGAGED, ACFT WAS DSNDING FROM 35000' WITH INTERMEDIATE LEVEL-OFFS, FOR A PLANNED LNDG AT SBA. IN LEVEL FLT AT 28000' ACFT WAS CLRED TO MAINTAIN 24000'. CLRNC WAS ACKNOWLEDGED AND NEW ALT SET IN MCP ALT SET WINDOW AND CHKED BY BOTH PLTS. LEVEL CHANGE WAS SELECTED ON MCP (AN AUTOPLT DSNT MODE) AND ACFT STARTED DOWN AT APPROX 3000 FPM. AT APPROX 26000' PNF CHKED OFF (WITH PF CONCURRENCE) FROM MONITORING ATC TO LISTEN TO SBA ATIS. TIME OFF ATC FREQ APPROX 1 MIN. AT APPROX 24000' PF RECEIVED FREQ CHANGE FROM ZLA AND WHEN CHKING IN WITH NEW CTLR, RPTED PASSING APPROX 23000 FOR 21000'--21000' BEING THE ALT SHOWING IN THE MCP ALT WINDOW, HOWEVER NOT SET BY EITHER PLT. CTLR ACKNOWLEDGED XMISSION THEN REQUESTED LAST ALT CLRNC. PF ONCE AGAIN RESPONDED 'FL210,' BECAUSE THAT WAS THE ALT SET IN MCP ALT WINDOW. CTLR ACKNOWLEDGED XMISSION AND SUBSEQUENTLY CLRED ACFT TO MAINTAIN FL220. PROB AREA: PNF OUT OF LOOP FOR APPROX 1 MIN WHILE OBTAINING ATIS WHICH WAS WORTH 3000' OF ALT LOS. PF ACCEPTED ALT SET IN MCP WINDOW AS CORRECT ALT FROM LAST CLRNC. UNCOMMANDED ALT CHANGE IN ELECTRONIC ALT SET WINDOW DUE SOFTWARE PROB? CORRECTIVE ACTION: GREATER DILIGENCE ON PART OF PLTS, ESPECIALLY WHEN ONLY ONE IS FLYING AND COMMUNICATING. UNCOMMANDED ALT CHANGE IS RECURRING PROB IN GLASS COCKPIT--NEED CHANGE IN SOFTWARE OF INSTALL A MORE TRADITIONAL ALT SET WINDOW.

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.

Air carrier medium large transport altitude deviation overshot during descent. Flight crew claims they set 240 in altitude alert, but approximately 1 minute later it read 210.