In-flight WX encounter resulted in altitude deviation from assigned and possible loss of separation.

Attributes
ACN	114660
Time
Date	198906
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : bna
State Reference	TN
Altitude	msl bound lower : 5000 msl bound upper : 5500
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bna
Operator	common carrier : air carrier
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	departure other enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 3000 flight time type : 1000
ASRS Report	114660
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 175 flight time total : 2500 flight time type : 800
ASRS Report	114545
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe inflight encounter : weather inflight encounter other
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 500
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

We saw traffic when we broke out of clouds. Air carrier flight xx bna-lex after takeoff and initial climb to 4000. Departure cleared us to 5000' and turned us from heading 110 degree to heading 010 degree maintain 5000'. We were level at 5000' and I turned toward 010 degree in a 30 degree bank to avoid some rapidly developing cumulus clouds. I had already reduced power approximately 25 percent so as to tighten my turn when we penetrated the before mentioned cloud mass. As we approached about 45 degree heading my vsi went from +/-0 to +1500 in just a couple seconds. I reduced power to flight idle with the attitude DOT on or slightly below the artificial horizon. The aircraft started to descend at about 5500', and we corrected back down as soon as we could, all the while the first officer was trying to get a word in to ATC to ask for a block of altitude temporarily. ATC had us turn back to about 030 degree but we were back on 5000' before we were on the heading. This was not an altitude bust because we forgot our altitude or did not understand we had been level for some time and had asked for higher much earlier and had been turned down. I explained to the first officer he is obviously holding us here because of traffic.

Original NASA ASRS Text

Title: INFLT WX ENCOUNTER RESULTED IN ALT DEVIATION FROM ASSIGNED AND POSSIBLE LOSS OF SEPARATION.

Narrative: WE SAW TFC WHEN WE BROKE OUT OF CLOUDS. ACR FLT XX BNA-LEX AFTER TKOF AND INITIAL CLIMB TO 4000. DEP CLRED US TO 5000' AND TURNED US FROM HDG 110 DEG TO HDG 010 DEG MAINTAIN 5000'. WE WERE LEVEL AT 5000' AND I TURNED TOWARD 010 DEG IN A 30 DEG BANK TO AVOID SOME RAPIDLY DEVELOPING CUMULUS CLOUDS. I HAD ALREADY REDUCED POWER APPROX 25 PERCENT SO AS TO TIGHTEN MY TURN WHEN WE PENETRATED THE BEFORE MENTIONED CLOUD MASS. AS WE APCHED ABOUT 45 DEG HDG MY VSI WENT FROM +/-0 TO +1500 IN JUST A COUPLE SECONDS. I REDUCED POWER TO FLT IDLE WITH THE ATTITUDE DOT ON OR SLIGHTLY BELOW THE ARTIFICIAL HORIZON. THE ACFT STARTED TO DSND AT ABOUT 5500', AND WE CORRECTED BACK DOWN AS SOON AS WE COULD, ALL THE WHILE THE F/O WAS TRYING TO GET A WORD IN TO ATC TO ASK FOR A BLOCK OF ALT TEMPORARILY. ATC HAD US TURN BACK TO ABOUT 030 DEG BUT WE WERE BACK ON 5000' BEFORE WE WERE ON THE HDG. THIS WAS NOT AN ALT BUST BECAUSE WE FORGOT OUR ALT OR DID NOT UNDERSTAND WE HAD BEEN LEVEL FOR SOME TIME AND HAD ASKED FOR HIGHER MUCH EARLIER AND HAD BEEN TURNED DOWN. I EXPLAINED TO THE F/O HE IS OBVIOUSLY HOLDING US HERE BECAUSE OF TFC.

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.