Air carrier flight crew deviated from altitude to avoid microburst virga and turbulence.

Attributes
ACN	312387
Time
Date	199508
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : den
State Reference	CO
Altitude	msl bound lower : 12000 msl bound upper : 12000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : den
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer pilot : cfi
Experience	flight time last 90 days : 170 flight time total : 10000
ASRS Report	312387
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were being vectored on an east downwind for runway 35L at den, virga was present in all quadrants. Windshear advisories were active (soon after, microburst advisories) and 1 aircraft had just gone around. We were headed for an area of virga and had requested lower, ATC had advised lower in a few mi. As we closed on the virga, we encountered moderate to severe turbulence. After checking TCASII for conflicting traffic, (none) the PF announced he was descending and advised ATC of this with the reason why. After approximately 500 ft the descent was stopped, ATC was contacted again and after a reprimand issued, a lower clearance. The remainder of the approach was completed without further complications.

Original NASA ASRS Text

Title: ACR FLC DEVIATED FROM ALT TO AVOID MICROBURST VIRGA AND TURB.

Narrative: WE WERE BEING VECTORED ON AN E DOWNWIND FOR RWY 35L AT DEN, VIRGA WAS PRESENT IN ALL QUADRANTS. WINDSHEAR ADVISORIES WERE ACTIVE (SOON AFTER, MICROBURST ADVISORIES) AND 1 ACFT HAD JUST GONE AROUND. WE WERE HEADED FOR AN AREA OF VIRGA AND HAD REQUESTED LOWER, ATC HAD ADVISED LOWER IN A FEW MI. AS WE CLOSED ON THE VIRGA, WE ENCOUNTERED MODERATE TO SEVERE TURB. AFTER CHKING TCASII FOR CONFLICTING TFC, (NONE) THE PF ANNOUNCED HE WAS DSNDING AND ADVISED ATC OF THIS WITH THE REASON WHY. AFTER APPROX 500 FT THE DSCNT WAS STOPPED, ATC WAS CONTACTED AGAIN AND AFTER A REPRIMAND ISSUED, A LOWER CLRNC. THE REMAINDER OF THE APCH WAS COMPLETED WITHOUT FURTHER COMPLICATIONS.

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.