Pilot of small aircraft cleared to descend to 4300'. Because of turbulence and WX conditions at 9000...

Attributes
ACN	110587
Time
Date	198905
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ikb
State Reference	NC
Altitude	msl bound lower : 3500 msl bound upper : 4300
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Small Aircraft
Flight Phase	cruise other descent other
Route In Use	enroute airway : v16
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 25 flight time total : 400
ASRS Report	110587
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : overshoot inflight encounter : weather non adherence : clearance
Independent Detector	other other : unspecified cockpit
Resolutory Action	controller : issued new clearance flight crew : regained aircraft control
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft was on an IFR flight plan on V16-136 to hmv VOR. Due to moderate turbulence encountered and possibility of icing, requested permission (granted) from ZTL to deviate to hickory municipal airport. Due to further increased turbulence and rain requested vectors to wilkesboro airport, nc, wince this was the closest airport and also requested lower altitude. Received permission to descend to 4300' from present altitude of 9000'. Near altitude of 5000' a strong down draft was encountered which caused our aircraft to descend below the last assigned altitude of 4300'. This occurred despite increased power to decrease our rate of descent. After descending to approximately 3500', we were in VFR conditions with ceilings between 4000-5000', and were no longer experiencing the previous turbulence, except for rain. Despite realizing our last assigned altitude was 4300', I elected to stay at this altitude because of improved WX conditions. ZTL then gave vectors to wilkesboro airport which we saw on the second vector and landed west/O incident. The main factor contributing to this incident was the turbulence causing an increased rate of descent despite full power. The best suggestion for prevented such an incident is to stay away from WX such as this, that may have associated vertical air movement, causing altitude deviations.

Original NASA ASRS Text

Title: PLT OF SMA CLEARED TO DESCEND TO 4300'. BECAUSE OF TURB AND WX CONDITIONS AT 9000' ACFT OVERSHOT DESCENT ALT BECAUSE OF TURBULENCE AND DESCENDED TO 3500'. CENTER ISSUED NEW CLRNC TO LAND AT IKB.

Narrative: ACFT WAS ON AN IFR FLT PLAN ON V16-136 TO HMV VOR. DUE TO MODERATE TURB ENCOUNTERED AND POSSIBILITY OF ICING, REQUESTED PERMISSION (GRANTED) FROM ZTL TO DEVIATE TO HICKORY MUNI ARPT. DUE TO FURTHER INCREASED TURB AND RAIN REQUESTED VECTORS TO WILKESBORO ARPT, NC, WINCE THIS WAS THE CLOSEST ARPT AND ALSO REQUESTED LOWER ALT. RECEIVED PERMISSION TO DSND TO 4300' FROM PRESENT ALT OF 9000'. NEAR ALT OF 5000' A STRONG DOWN DRAFT WAS ENCOUNTERED WHICH CAUSED OUR ACFT TO DSND BELOW THE LAST ASSIGNED ALT OF 4300'. THIS OCCURRED DESPITE INCREASED PWR TO DECREASE OUR RATE OF DSCNT. AFTER DSNDING TO APPROX 3500', WE WERE IN VFR CONDITIONS WITH CEILINGS BTWN 4000-5000', AND WERE NO LONGER EXPERIENCING THE PREVIOUS TURB, EXCEPT FOR RAIN. DESPITE REALIZING OUR LAST ASSIGNED ALT WAS 4300', I ELECTED TO STAY AT THIS ALT BECAUSE OF IMPROVED WX CONDITIONS. ZTL THEN GAVE VECTORS TO WILKESBORO ARPT WHICH WE SAW ON THE SECOND VECTOR AND LANDED W/O INCIDENT. THE MAIN FACTOR CONTRIBUTING TO THIS INCIDENT WAS THE TURB CAUSING AN INCREASED RATE OF DSCNT DESPITE FULL PWR. THE BEST SUGGESTION FOR PREVENTED SUCH AN INCIDENT IS TO STAY AWAY FROM WX SUCH AS THIS, THAT MAY HAVE ASSOCIATED VERT AIR MOVEMENT, CAUSING ALT DEVIATIONS.

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.

Pilot of small aircraft cleared to descend to 4300'. Because of turbulence and WX conditions at 9000' aircraft overshot descent altitude because of turbulence and descended to 3500'. Center issued new clearance to land at ikb.