Altitude deviation as small aircraft is unable to maintain assigned IFR altitude in turbulent icing ...

Attributes
ACN	206270
Time
Date	199204
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : mol
State Reference	VA
Altitude	msl bound lower : 6700 msl bound upper : 7000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Route In Use	enroute airway : v143
Flight Plan	IFR
Person 1
Affiliation	Other
Function	instruction : instructor oversight : pic
Qualification	pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 100 flight time total : 700 flight time type : 500
ASRS Report	206270
Person 2
Affiliation	Other
Function	flight crew : single pilot instruction : trainee
Qualification	pilot : private
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : unable other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Normal IFR flight with a few vectors to avoid IMC icing altitudes. Continuous light moderate turbulence and mountain waves causing need for occasional full power to best rate of climb airspeed to maintain altitude. However, after approximately 10 mins of light turbulence full power airspeed, the small aircraft could no longer maintain altitude. Full carburetor heat was already applied -- and turning it off made no change. After advising center we were unable to maintain altitude, we received vectors to cho. While diverting fuel selector changed alternately to left, right, both with no result. At 10 mi from cho, the problem cleared up but we elected to land anyway and spend the night. At first, I was unwilling to accept a problem existed since it is not unusual to exceed the small aircraft's climb capability (400 FPM at 7000 ft) for a few mins in mountains. After 10 mins prior to departure during light moderate snow showers, I feel that ice may have formed in the fuel lines (temperature aloft was -10 degree C), even though preflight inspection revealed nothing.

Original NASA ASRS Text

Title: ALTDEV AS SMA IS UNABLE TO MAINTAIN ASSIGNED IFR ALT IN TURBULENT ICING CONDITIONS.

Narrative: NORMAL IFR FLT WITH A FEW VECTORS TO AVOID IMC ICING ALTS. CONTINUOUS LIGHT MODERATE TURB AND MOUNTAIN WAVES CAUSING NEED FOR OCCASIONAL FULL PWR TO BEST RATE OF CLB AIRSPD TO MAINTAIN ALT. HOWEVER, AFTER APPROX 10 MINS OF LIGHT TURB FULL PWR AIRSPD, THE SMA COULD NO LONGER MAINTAIN ALT. FULL CARB HEAT WAS ALREADY APPLIED -- AND TURNING IT OFF MADE NO CHANGE. AFTER ADVISING CTR WE WERE UNABLE TO MAINTAIN ALT, WE RECEIVED VECTORS TO CHO. WHILE DIVERTING FUEL SELECTOR CHANGED ALTERNATELY TO L, R, BOTH WITH NO RESULT. AT 10 MI FROM CHO, THE PROBLEM CLRED UP BUT WE ELECTED TO LAND ANYWAY AND SPEND THE NIGHT. AT FIRST, I WAS UNWILLING TO ACCEPT A PROBLEM EXISTED SINCE IT IS NOT UNUSUAL TO EXCEED THE SMA'S CLB CAPABILITY (400 FPM AT 7000 FT) FOR A FEW MINS IN MOUNTAINS. AFTER 10 MINS PRIOR TO DEP DURING LIGHT MODERATE SNOW SHOWERS, I FEEL THAT ICE MAY HAVE FORMED IN THE FUEL LINES (TEMP ALOFT WAS -10 DEG C), EVEN THOUGH PREFLT INSPECTION REVEALED NOTHING.

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.

Altitude deviation as small aircraft is unable to maintain assigned IFR altitude in turbulent icing conditions.