VFR on top at wrong altitude. Confusing clearance from ATC.

Attributes
ACN	107494
Time
Date	198903
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bna
State Reference	TN
Altitude	msl bound lower : 9000 msl bound upper : 9000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 50 flight time total : 1000 flight time type : 800
ASRS Report	107494
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	non adherence : far non adherence : published procedure other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation other

Narrative:

Because of moderately severe turbulence in clouds, pilot requested and received clearance from ZME for VFR on top. Further advised by center that if unable to maintain VFR above 9000, advise them. Cloud tops rose from 8500' to 9000' the following 15 mins. 4 attempts to contact center by pilot were unsuccessful (attempting to advise, request clearance to 6000'). Center finally contacted pilot with 'say altitude,' advise at 9000' with request for longer. Center responded that our clearance was only for 8500', expedite descent to 6000'. Re-encountered moderately severe turbulence during rapid descent (the relatively higher airspeed was a factor). I believe controller misunderstood VFR on top clearance. I was under VFR conditions at 9000' and was complying with my clearance. If this caused a conflict with IFR traffic at that altitude, the controller should not have issued it.

Original NASA ASRS Text

Title: VFR ON TOP AT WRONG ALT. CONFUSING CLRNC FROM ATC.

Narrative: BECAUSE OF MODERATELY SEVERE TURB IN CLOUDS, PLT REQUESTED AND RECEIVED CLRNC FROM ZME FOR VFR ON TOP. FURTHER ADVISED BY CENTER THAT IF UNABLE TO MAINTAIN VFR ABOVE 9000, ADVISE THEM. CLOUD TOPS ROSE FROM 8500' TO 9000' THE FOLLOWING 15 MINS. 4 ATTEMPTS TO CONTACT CENTER BY PLT WERE UNSUCCESSFUL (ATTEMPTING TO ADVISE, REQUEST CLRNC TO 6000'). CENTER FINALLY CONTACTED PLT WITH 'SAY ALT,' ADVISE AT 9000' WITH REQUEST FOR LONGER. CENTER RESPONDED THAT OUR CLRNC WAS ONLY FOR 8500', EXPEDITE DSCNT TO 6000'. RE-ENCOUNTERED MODERATELY SEVERE TURB DURING RAPID DSCNT (THE RELATIVELY HIGHER AIRSPD WAS A FACTOR). I BELIEVE CTLR MISUNDERSTOOD VFR ON TOP CLRNC. I WAS UNDER VFR CONDITIONS AT 9000' AND WAS COMPLYING WITH MY CLRNC. IF THIS CAUSED A CONFLICT WITH IFR TFC AT THAT ALT, THE CTLR SHOULD NOT HAVE ISSUED IT.

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.