An light transport crew, unknowingly, disengaged the altitude hold causing an altitude excursion.

Attributes
ACN	505380
Time
Date	200103
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : tul.airport
State Reference	OK
Altitude	msl bound lower : 9000 msl bound upper : 16000
Environment
Flight Conditions	IMC
Weather Elements	Ice
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme.artcc tower : iad.tower
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Operating Under FAR Part	Part 135
Navigation In Use	other vortac
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial
Experience	flight time last 90 days : 270 flight time total : 18000 flight time type : 16000
ASRS Report	505380
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter : turbulence non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance Weather
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Altitude deviation of about 1000 ft occurred. Aircraft was in moderate turbulence and icing conditions, IMC. Clearance given pilot's discretion 9000 ft. First officer selected 9000 ft in altitude selector, altimeter was given with a large variance to correct to. Apparently, autoplt altitude hold disengaged, both pilots were reviewing approach plates. Aircraft climbed, unnoticed, to about 16000 ft. Once noticed, aircraft was descended to 9000 ft at pilot's discretion. No ATC warning or recognition of deviation was given. There were no other aircraft anywhere near our airspace.

Original NASA ASRS Text

Title: AN LTT CREW, UNKNOWINGLY, DISENGAGED THE ALT HOLD CAUSING AN ALT EXCURSION.

Narrative: ALTDEV OF ABOUT 1000 FT OCCURRED. ACFT WAS IN MODERATE TURB AND ICING CONDITIONS, IMC. CLRNC GIVEN PLT'S DISCRETION 9000 FT. FO SELECTED 9000 FT IN ALT SELECTOR, ALTIMETER WAS GIVEN WITH A LARGE VARIANCE TO CORRECT TO. APPARENTLY, AUTOPLT ALT HOLD DISENGAGED, BOTH PLTS WERE REVIEWING APCH PLATES. ACFT CLBED, UNNOTICED, TO ABOUT 16000 FT. ONCE NOTICED, ACFT WAS DSNDED TO 9000 FT AT PLT'S DISCRETION. NO ATC WARNING OR RECOGNITION OF DEV WAS GIVEN. THERE WERE NO OTHER ACFT ANYWHERE NEAR OUR AIRSPACE.

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.