Light transport has autoplt disengage, climbs above assigned. Causes TCASII RA for medium large tran...

Attributes
ACN	226546
Time
Date	199211
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : pub
State Reference	CO
Altitude	msl bound lower : 27000 msl bound upper : 27400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	other
Make Model Name	Small Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 100
ASRS Report	226546
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : clearance non adherence : required legal separation other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 8000 vertical : 700
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flying an light transport from pueblo, co, to davenport, ia, the controller had leveled us off at FL270 until crossing traffic cleared. The crossing traffic was an air carrier medium large transport with TCASII. The autoplt on the light transport disengaged for an unknown reason and the aircraft began a slow climb. Any autoplt disengagement is accompanied by a tone to alert the flight crew of the abnormality. Both pilots either missed the tone or the tone did not sound. The aircraft climbed 300 ft and the altitude select tone warned of the deviation. Correction was made and the aircraft stopped the climb at approximately 400 ft above assigned altitude -- FL274. The medium large transport crew received a TCASII alert and questioned the controller as to the light transport altitude. The controller still had the light transport altitude at FL270. Medium large transport TCASII showed the medium large transport at FL274 and still climbing. The autoplt was monitored for the remainder of the trip for any similar disengagements, none occurred. An autoplt check was performed prior to the next leg and all checks were normal.

Original NASA ASRS Text

Title: LTT HAS AUTOPLT DISENGAGE, CLBS ABOVE ASSIGNED. CAUSES TCASII RA FOR MLG.

Narrative: FLYING AN LTT FROM PUEBLO, CO, TO DAVENPORT, IA, THE CTLR HAD LEVELED US OFF AT FL270 UNTIL XING TFC CLRED. THE XING TFC WAS AN ACR MLG WITH TCASII. THE AUTOPLT ON THE LTT DISENGAGED FOR AN UNKNOWN REASON AND THE ACFT BEGAN A SLOW CLB. ANY AUTOPLT DISENGAGEMENT IS ACCOMPANIED BY A TONE TO ALERT THE FLC OF THE ABNORMALITY. BOTH PLTS EITHER MISSED THE TONE OR THE TONE DID NOT SOUND. THE ACFT CLBED 300 FT AND THE ALT SELECT TONE WARNED OF THE DEV. CORRECTION WAS MADE AND THE ACFT STOPPED THE CLB AT APPROX 400 FT ABOVE ASSIGNED ALT -- FL274. THE MLG CREW RECEIVED A TCASII ALERT AND QUESTIONED THE CTLR AS TO THE LTT ALT. THE CTLR STILL HAD THE LTT ALT AT FL270. MLG TCASII SHOWED THE MLG AT FL274 AND STILL CLBING. THE AUTOPLT WAS MONITORED FOR THE REMAINDER OF THE TRIP FOR ANY SIMILAR DISENGAGEMENTS, NONE OCCURRED. AN AUTOPLT CHK WAS PERFORMED PRIOR TO THE NEXT LEG AND ALL CHKS WERE NORMAL.

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.

Light transport has autoplt disengage, climbs above assigned. Causes TCASII RA for medium large transport.