Narrative:

During preflight; we noted a SIGMET for volcanic ash from mt okmok in the aleutian islands and were surprised to see that we would be heading near this area. Further study of the SIGMET; however; showed that the ash cloud was predicted to head southeast. Flying north of the volcano should keep us out of the ash. After departure; we received an updated SIGMET that now showed the ash cloud would be heading northeast; topping out at FL350. We plotted out the coordinates of the ash cloud included in the SIGMET on our FMC and could see in map view that our route of flight would take us straight through the affected area. I informed dispatch that it looks like we were going to be close to the SIGMET area. He informed us that they were looking at a rerte further to the north. He also sent us the proposed route that other aircraft were taking. We studied the new route mapped it out on our FMC; and found that if we followed the rerte; we would pass well north of the SIGMET area. Around this time; we established VHF communications with zan and queried him on the ash cloud; the rerte; and if he had any PIREPS for us. The controller said that folks were being rerted north but no PIREPS were available. We also requested and received FL370; both for performance and to stay above the SIGMET area. Not long after our conversation with ATC; we received a new route via cpdlc. We studied it; loaded it into the FMC; then accepted and executed the route change. It was the same routing discussed with dispatch and we were confident that the new route would keep us well north of the ash cloud. We were passing north of the SIGMET area; somewhere near kodiak island when it was time for a crew change. The captain has been on break and I was to go on my break next. About 5 or 10 mins before the captain came up; I noticed a strange halo in the windshield. It was similar to the rainbow effect when flying in high; thin cirrus clouds but not as uniform. The 'rainbow' was brighter and wider in some areas of the halo and 'spiky' in appearance. I also noticed brown spots on my windshield that looked like insects but were all uniform in size. I pointed them out to the captain; who had since returned to his seat; and he saw them as well. I did not smell anything unusual; saw no fluctuations or changes in our engine instruments; and could not see any change in opacity to our windshield. Still; we did suspect that we had just experienced an ash encounter but since my break was starting; I left it to the captain and relief first officer to handle the situation. At that point; I left for my break. When I returned; I was informed that both the dispatcher and the captain had written up the incident as a possible ash encounter. When we landed; we were met by mechanics who initially did not see the brown specks on the windshield but when we described the encounter; they said that what we described was almost verbatim out of their maintenance manual as an ash encounter. Also; a mechanic opened the side window and brushed his hand over my windshield. He saw a gray; gritty substance on his palms. The discussion with the mechanics was related to me by the captain as I had left to try and catch my commuter flight home.

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Original NASA ASRS Text

Title: B777-200 FLT CREW FLIES THROUGH VOLCANIC ASH N OF ALEUTIAN ISLANDS.

Narrative: DURING PREFLT; WE NOTED A SIGMET FOR VOLCANIC ASH FROM MT OKMOK IN THE ALEUTIAN ISLANDS AND WERE SURPRISED TO SEE THAT WE WOULD BE HEADING NEAR THIS AREA. FURTHER STUDY OF THE SIGMET; HOWEVER; SHOWED THAT THE ASH CLOUD WAS PREDICTED TO HEAD SE. FLYING N OF THE VOLCANO SHOULD KEEP US OUT OF THE ASH. AFTER DEP; WE RECEIVED AN UPDATED SIGMET THAT NOW SHOWED THE ASH CLOUD WOULD BE HEADING NE; TOPPING OUT AT FL350. WE PLOTTED OUT THE COORDINATES OF THE ASH CLOUD INCLUDED IN THE SIGMET ON OUR FMC AND COULD SEE IN MAP VIEW THAT OUR RTE OF FLT WOULD TAKE US STRAIGHT THROUGH THE AFFECTED AREA. I INFORMED DISPATCH THAT IT LOOKS LIKE WE WERE GOING TO BE CLOSE TO THE SIGMET AREA. HE INFORMED US THAT THEY WERE LOOKING AT A RERTE FURTHER TO THE N. HE ALSO SENT US THE PROPOSED RTE THAT OTHER ACFT WERE TAKING. WE STUDIED THE NEW RTE MAPPED IT OUT ON OUR FMC; AND FOUND THAT IF WE FOLLOWED THE RERTE; WE WOULD PASS WELL N OF THE SIGMET AREA. AROUND THIS TIME; WE ESTABLISHED VHF COMS WITH ZAN AND QUERIED HIM ON THE ASH CLOUD; THE RERTE; AND IF HE HAD ANY PIREPS FOR US. THE CTLR SAID THAT FOLKS WERE BEING RERTED N BUT NO PIREPS WERE AVAILABLE. WE ALSO REQUESTED AND RECEIVED FL370; BOTH FOR PERFORMANCE AND TO STAY ABOVE THE SIGMET AREA. NOT LONG AFTER OUR CONVERSATION WITH ATC; WE RECEIVED A NEW RTE VIA CPDLC. WE STUDIED IT; LOADED IT INTO THE FMC; THEN ACCEPTED AND EXECUTED THE RTE CHANGE. IT WAS THE SAME ROUTING DISCUSSED WITH DISPATCH AND WE WERE CONFIDENT THAT THE NEW RTE WOULD KEEP US WELL N OF THE ASH CLOUD. WE WERE PASSING N OF THE SIGMET AREA; SOMEWHERE NEAR KODIAK ISLAND WHEN IT WAS TIME FOR A CREW CHANGE. THE CAPT HAS BEEN ON BREAK AND I WAS TO GO ON MY BREAK NEXT. ABOUT 5 OR 10 MINS BEFORE THE CAPT CAME UP; I NOTICED A STRANGE HALO IN THE WINDSHIELD. IT WAS SIMILAR TO THE RAINBOW EFFECT WHEN FLYING IN HIGH; THIN CIRRUS CLOUDS BUT NOT AS UNIFORM. THE 'RAINBOW' WAS BRIGHTER AND WIDER IN SOME AREAS OF THE HALO AND 'SPIKY' IN APPEARANCE. I ALSO NOTICED BROWN SPOTS ON MY WINDSHIELD THAT LOOKED LIKE INSECTS BUT WERE ALL UNIFORM IN SIZE. I POINTED THEM OUT TO THE CAPT; WHO HAD SINCE RETURNED TO HIS SEAT; AND HE SAW THEM AS WELL. I DID NOT SMELL ANYTHING UNUSUAL; SAW NO FLUCTUATIONS OR CHANGES IN OUR ENG INSTS; AND COULD NOT SEE ANY CHANGE IN OPACITY TO OUR WINDSHIELD. STILL; WE DID SUSPECT THAT WE HAD JUST EXPERIENCED AN ASH ENCOUNTER BUT SINCE MY BREAK WAS STARTING; I LEFT IT TO THE CAPT AND RELIEF FO TO HANDLE THE SITUATION. AT THAT POINT; I LEFT FOR MY BREAK. WHEN I RETURNED; I WAS INFORMED THAT BOTH THE DISPATCHER AND THE CAPT HAD WRITTEN UP THE INCIDENT AS A POSSIBLE ASH ENCOUNTER. WHEN WE LANDED; WE WERE MET BY MECHS WHO INITIALLY DID NOT SEE THE BROWN SPECKS ON THE WINDSHIELD BUT WHEN WE DESCRIBED THE ENCOUNTER; THEY SAID THAT WHAT WE DESCRIBED WAS ALMOST VERBATIM OUT OF THEIR MAINT MANUAL AS AN ASH ENCOUNTER. ALSO; A MECH OPENED THE SIDE WINDOW AND BRUSHED HIS HAND OVER MY WINDSHIELD. HE SAW A GRAY; GRITTY SUBSTANCE ON HIS PALMS. THE DISCUSSION WITH THE MECHS WAS RELATED TO ME BY THE CAPT AS I HAD LEFT TO TRY AND CATCH MY COMMUTER FLT HOME.

Data retrieved from NASA's ASRS site as of May 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.