B737 flight encounters volcanic ash cloud while in cruise and crew deviates. Dispatcher noted that h...

Attributes
ACN	684295
Time
Date	200601
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : yak.vor
State Reference	AK
Altitude	msl bound lower : 31000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	artcc : zan.artcc
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	other personnel
Qualification	other
ASRS Report	684295
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	inflight encounter other
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment
Consequence	other
Supplementary
Problem Areas	Environmental Factor
Primary Problem	Environmental Factor

Narrative:

Air carrier X encountered what he believed to be a cloud of ash at FL310; just west of yak VOR. He asked and received permission from zan to climb up to FL330 and deviate around and above supposed ash cloud. Evidence of ash cloud by crew was 'dirty; musty odor...which lasted about 10 mins and brown colored stratified layer.' captain made maintenance write-up; and aircraft was taken OTS for ash check upon arrival in sea. As far as dispatch of this particular flight; I had rerted aircraft along joh; yak; and bka as a precaution to avoid any ash; which according to SIGMET and as plot was no factor. Coordinates for SIGMET were 40 wsw ena--90 east mdo...240 south bka...60 southwest hom...40 wsw ena...ash blw 450...thus; SIGMET placed area of ash quite a ways off of anc-sea route of flight. Wind experts obviously were off on calculations; because the first I heard of ash was air carrier Y; sea-anc giving me a PIREP of ash cloud FL310-FL340 from bka-wrg. Shortly thereafter; a new plot and SIGMET. Updated ash cloud based on our PIREPS.

Original NASA ASRS Text

Title: B737 FLT ENCOUNTERS VOLCANIC ASH CLOUD WHILE IN CRUISE AND CREW DEVIATES. DISPATCHER NOTED THAT HE HAD RERTED THE ACFT FROM ITS INITIAL COURSE IN ANTICIPATION OF THE CLOUD; HOWEVER; THE WIND FORECAST HAD BEEN INCORRECT.

Narrative: ACR X ENCOUNTERED WHAT HE BELIEVED TO BE A CLOUD OF ASH AT FL310; JUST W OF YAK VOR. HE ASKED AND RECEIVED PERMISSION FROM ZAN TO CLB UP TO FL330 AND DEVIATE AROUND AND ABOVE SUPPOSED ASH CLOUD. EVIDENCE OF ASH CLOUD BY CREW WAS 'DIRTY; MUSTY ODOR...WHICH LASTED ABOUT 10 MINS AND BROWN COLORED STRATIFIED LAYER.' CAPT MADE MAINT WRITE-UP; AND ACFT WAS TAKEN OTS FOR ASH CHK UPON ARR IN SEA. AS FAR AS DISPATCH OF THIS PARTICULAR FLT; I HAD RERTED ACFT ALONG JOH; YAK; AND BKA AS A PRECAUTION TO AVOID ANY ASH; WHICH ACCORDING TO SIGMET AND AS PLOT WAS NO FACTOR. COORDINATES FOR SIGMET WERE 40 WSW ENA--90 E MDO...240 S BKA...60 SW HOM...40 WSW ENA...ASH BLW 450...THUS; SIGMET PLACED AREA OF ASH QUITE A WAYS OFF OF ANC-SEA RTE OF FLT. WIND EXPERTS OBVIOUSLY WERE OFF ON CALCULATIONS; BECAUSE THE FIRST I HEARD OF ASH WAS ACR Y; SEA-ANC GIVING ME A PIREP OF ASH CLOUD FL310-FL340 FROM BKA-WRG. SHORTLY THEREAFTER; A NEW PLOT AND SIGMET. UPDATED ASH CLOUD BASED ON OUR PIREPS.

Data retrieved from NASA's ASRS site as of January 2009 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.

B737 flight encounters volcanic ash cloud while in cruise and crew deviates. Dispatcher noted that he had rerted the aircraft from its initial course in anticipation of the cloud; however; the wind forecast had been incorrect.