Altitude deviation excursion from assigned altitude.

Attributes
ACN	117988
Time
Date	198907
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : dfw
State Reference	TX
Altitude	msl bound lower : 10000 msl bound upper : 10300
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : dfw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	departure other enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : instrument
Experience	flight time last 90 days : 50 flight time total : 8000 flight time type : 50
ASRS Report	117988
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 3500 flight time type : 300
ASRS Report	118011
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Normal departure out of dfw to south on runway 17R. Level at 10000' directed to maintain 230 KTS, then 250 KTS. Level off was manual and aircraft stable at 250 KTS and 10000' on radar vectors. VNAV was engaged. Turned autoplt on and confirmed VNAV level was annunciated on annunciator panel. Reached over for chart anticipating departure radial change and first officer said aircraft climbing. I disengaged autoplt and releveled aircraft which was climbing at possibly 400 FPM through 10200'. Altitude reached about 10250, possibly 10300', before I releveled at 10000'. Controller did call and reinstruct to maintain 10000'. Previous traffic was called inbound at 11000'. I reengaged autoplt and again confirmed VNAV level and aircraft stable 250 KTS and 10000'. Once again the autoplt stated a slow climb, at which time I disengaged and reengaged again. The aircraft held altitude normally. We were then cleared on course and to a higher altitude. VNAV level is supposed to maintain altitude hold, but in this case drifted. We tried to check the system again at cruise altitude and it operated normally. Obvious constant vigilance is required of the medium large transport flight guidance control panel, as well as basic instruments. Callback conversation with reporter revealed the following: reporter states that this medium large transport is commonly experiencing this problem. The VNAV function has recently been activated in climb and numerous reports have been received by the air carrier describing similar incidents. He states that because he is new to type, he was concerned that his operating technique might be contributory, but believes that it is not connected to the problem. He is very experienced with autoflt aircraft, having just completed 3 yrs on an advanced tech widebody transport. Supplemental information from acn 118011: we immediately received a revised clearance to intercept the 078 degree right out of dfw, and the captain began programming the FMS for the revised route.

Original NASA ASRS Text

Title: ALT DEVIATION EXCURSION FROM ASSIGNED ALT.

Narrative: NORMAL DEP OUT OF DFW TO S ON RWY 17R. LEVEL AT 10000' DIRECTED TO MAINTAIN 230 KTS, THEN 250 KTS. LEVEL OFF WAS MANUAL AND ACFT STABLE AT 250 KTS AND 10000' ON RADAR VECTORS. VNAV WAS ENGAGED. TURNED AUTOPLT ON AND CONFIRMED VNAV LEVEL WAS ANNUNCIATED ON ANNUNCIATOR PANEL. REACHED OVER FOR CHART ANTICIPATING DEP RADIAL CHANGE AND F/O SAID ACFT CLBING. I DISENGAGED AUTOPLT AND RELEVELED ACFT WHICH WAS CLBING AT POSSIBLY 400 FPM THROUGH 10200'. ALT REACHED ABOUT 10250, POSSIBLY 10300', BEFORE I RELEVELED AT 10000'. CTLR DID CALL AND REINSTRUCT TO MAINTAIN 10000'. PREVIOUS TFC WAS CALLED INBND AT 11000'. I REENGAGED AUTOPLT AND AGAIN CONFIRMED VNAV LEVEL AND ACFT STABLE 250 KTS AND 10000'. ONCE AGAIN THE AUTOPLT STATED A SLOW CLB, AT WHICH TIME I DISENGAGED AND REENGAGED AGAIN. THE ACFT HELD ALT NORMALLY. WE WERE THEN CLRED ON COURSE AND TO A HIGHER ALT. VNAV LEVEL IS SUPPOSED TO MAINTAIN ALT HOLD, BUT IN THIS CASE DRIFTED. WE TRIED TO CHK THE SYS AGAIN AT CRUISE ALT AND IT OPERATED NORMALLY. OBVIOUS CONSTANT VIGILANCE IS REQUIRED OF THE MLG FLT GUIDANCE CONTROL PANEL, AS WELL AS BASIC INSTRUMENTS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATES THAT THIS MLG IS COMMONLY EXPERIENCING THIS PROB. THE VNAV FUNCTION HAS RECENTLY BEEN ACTIVATED IN CLB AND NUMEROUS RPTS HAVE BEEN RECEIVED BY THE ACR DESCRIBING SIMILAR INCIDENTS. HE STATES THAT BECAUSE HE IS NEW TO TYPE, HE WAS CONCERNED THAT HIS OPERATING TECHNIQUE MIGHT BE CONTRIBUTORY, BUT BELIEVES THAT IT IS NOT CONNECTED TO THE PROB. HE IS VERY EXPERIENCED WITH AUTOFLT ACFT, HAVING JUST COMPLETED 3 YRS ON AN ADVANCED TECH WDB. SUPPLEMENTAL INFO FROM ACN 118011: WE IMMEDIATELY RECEIVED A REVISED CLRNC TO INTERCEPT THE 078 DEG R OUT OF DFW, AND THE CAPT BEGAN PROGRAMMING THE FMS FOR THE REVISED ROUTE.

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.