Altitude excursion in ZTL airspace.

Attributes
ACN	404152
Time
Date	199806
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : lvt
State Reference	KY
Altitude	msl bound lower : 34700 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl tower : vny
Operator	general aviation : corporate
Make Model Name	Falcon 20FJF/20C/20D/20E/20F
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 50 flight time total : 10000 flight time type : 500
ASRS Report	404152
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument pilot : cfi
Experience	flight time last 90 days : 97 flight time total : 7928 flight time type : 1165
ASRS Report	404491
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While in cruise flight at FL350, nwbound, direct from atl- sbn, paralleling J89 using GPS navigation, the air crew was engaged in conversation with a passenger inquiring about the flight schedule and requesting a change in cabin temperature. While we were momentarily distraction, the AP103 autoplt altitude hold function apparently disengaged without our knowledge until the 300 ft warning bell activated at FL347. I immediately disengaged the autoplt completely and re- established flight at FL350. The center controller asked us to check our altitude, and we reported FL349, as we were already nearly back to FL350. The excursion was so gradual as to be unnoticed, and the aircraft did not descend below FL347. This type of performance is so common with the AP103 autoplt, that it is not mnps certifiable. A very high level of vigilance is required to prevent a recurrence of this type incident, and we have altered our crew procedures accordingly. Callback conversation with reporter revealed the following information: pilot reports that he has spoken to other operators of this aircraft which are equipped with the AP103 autoplt. All report that this autoplt will drift off altitude while the altitude hold feature is engaged.

Original NASA ASRS Text

Title: ALT EXCURSION IN ZTL AIRSPACE.

Narrative: WHILE IN CRUISE FLT AT FL350, NWBOUND, DIRECT FROM ATL- SBN, PARALLELING J89 USING GPS NAV, THE AIR CREW WAS ENGAGED IN CONVERSATION WITH A PAX INQUIRING ABOUT THE FLT SCHEDULE AND REQUESTING A CHANGE IN CABIN TEMP. WHILE WE WERE MOMENTARILY DISTR, THE AP103 AUTOPLT ALT HOLD FUNCTION APPARENTLY DISENGAGED WITHOUT OUR KNOWLEDGE UNTIL THE 300 FT WARNING BELL ACTIVATED AT FL347. I IMMEDIATELY DISENGAGED THE AUTOPLT COMPLETELY AND RE- ESTABLISHED FLT AT FL350. THE CTR CTLR ASKED US TO CHK OUR ALT, AND WE RPTED FL349, AS WE WERE ALREADY NEARLY BACK TO FL350. THE EXCURSION WAS SO GRADUAL AS TO BE UNNOTICED, AND THE ACFT DID NOT DSND BELOW FL347. THIS TYPE OF PERFORMANCE IS SO COMMON WITH THE AP103 AUTOPLT, THAT IT IS NOT MNPS CERTIFIABLE. A VERY HIGH LEVEL OF VIGILANCE IS REQUIRED TO PREVENT A RECURRENCE OF THIS TYPE INCIDENT, AND WE HAVE ALTERED OUR CREW PROCS ACCORDINGLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: PLT RPTS THAT HE HAS SPOKEN TO OTHER OPERATORS OF THIS ACFT WHICH ARE EQUIPPED WITH THE AP103 AUTOPLT. ALL RPT THAT THIS AUTOPLT WILL DRIFT OFF ALT WHILE THE ALT HOLD FEATURE IS ENGAGED.

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.