Light twin descends below clearance altitude.

Attributes
ACN	119924
Time
Date	198908
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : gll
State Reference	CO
Altitude	msl bound lower : 16000 msl bound upper : 17000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv tower : ric
Operator	general aviation : personal
Make Model Name	Small Aircraft
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial pilot : cfi
Experience	flight time last 90 days : 30 flight time total : 1100 flight time type : 20
ASRS Report	119924
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft was being flown for a maintenance check on the rear engine. IFR clearance was obtained to go to FL200 to test out turbo system on rear engine. Clearance was direct cheyenne VOR FL200 then direct gill VOR. Pilot asked for descent to 17,500 MSL and was given 17,000 MSL as an altitude. During descent the rear engine fuel flow started to fluctuate. Pilot got preoccupied with rear engine manifold pressure/fuel flow/temperature problems and descended below the assigned altitude by 500-1000'.

Original NASA ASRS Text

Title: LIGHT TWIN DESCENDS BELOW CLRNC ALT.

Narrative: ACFT WAS BEING FLOWN FOR A MAINT CHECK ON THE REAR ENGINE. IFR CLRNC WAS OBTAINED TO GO TO FL200 TO TEST OUT TURBO SYSTEM ON REAR ENGINE. CLRNC WAS DIRECT CHEYENNE VOR FL200 THEN DIRECT GILL VOR. PLT ASKED FOR DSCNT TO 17,500 MSL AND WAS GIVEN 17,000 MSL AS AN ALT. DURING DSCNT THE REAR ENGINE FUEL FLOW STARTED TO FLUCTUATE. PLT GOT PREOCCUPIED WITH REAR ENGINE MANIFOLD PRESSURE/FUEL FLOW/TEMP PROBLEMS AND DESCENDED BELOW THE ASSIGNED ALT BY 500-1000'.

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.