FARLIG ASKE: Vulkanen Mayon spyr ut røyk og aske på Filippinene. (Foto: Nelson Salting)
FARLIG ASKE: Vulkanen Mayon spyr ut røyk og aske på Filippinene. (Foto: Nelson Salting)

Asken kan sandblåse vinduene

Derfor er det farlig å fly inn i vulkansk aske.

All flytrafikk i Norge er innstilt torsdag. Aske fra vulkanutbruddet på Island utgjør en stor fare for flytrafikken.

Basesjef for SAS-pilotene i Oslo, Eivind Bjurstrøm, forklarer hva som kan skje:

– Asken kan tette en del av systemene våre, alle de systemene som krever noe utenfra og inn i flyet. Der kan denne asken skape store problemer. I tillegg kan den sandblåse både elementer i motoren og også faktisk vinduene foran i flyet, som gjør at flygemaskinen ikke virker som den skal. I verste fall kan motorer stanse. Det har skjedd ved to anledninger tidligere, forteller Bjurstrøm.

Alvorlige konsekvenser

I begge tilfellene klarte pilotene å få i gang motorene så flyene kunne landes trygt. Er man ikke så heldig, må man ta seg ned der man er.

SAS-SJEF PÅ GARDERMOEN: Eivind Bjurstrøm. (Foto: Gorm Røseth)
SAS-SJEF PÅ GARDERMOEN: Eivind Bjurstrøm. (Foto: Gorm Røseth)

– Det kan være hvor som helst, det kan være i skogområder, fjellområder eller over havet. Så det hadde blitt alvorlige hendelser, sier Bjurstrøm.

Også flyets kommunikasjonssystemer kan bli satt ut av spill av asken. Når partiklene treffer flykroppen, vil de bygge opp statisk elektrisitet som kan forstyrre radiosignalene til og fra flyet.

– Det blir mye støy som gjør at det blir umulig å kommunisere, sier Bjurstrøm.

Speedbird 9

Ett av de mest dramatiske tilfellene skjedde med en Boeing 747 fra British Airways 24. juni 1982 over Indonesia. Hendelsen kalles gjerne Speedbird 9 etter flyets kallesignal, eller Jakarta-hendelsen. Hendelsen er beskrevet utførlig i en Wikipedia-artikkel.

Uten at pilotene kunne se aske eller noe annet unormalt, oppdaget de at noe skjedde med vinduene i cockpit. Flygerne skrudde på avisingsanlegget i motorene og ba passasjerene feste setebeltene.

Kort tid etter kom det røyk inn i kabinen, og passasjerer merket at det oppsto en lyseffekt foran motorene.

JUMBOJET: Det var en flymaskin av denne typen som fløy inn i
  vulkansk aske over Indonesia. Bildet er tatt i Washington i 2008. (Foto:
  Karen Bleier)
JUMBOJET: Det var en flymaskin av denne typen som fløy inn i vulkansk aske over Indonesia. Bildet er tatt i Washington i 2008. (Foto: Karen Bleier)

Motorene stanset

Etter to minutter stanset motor nummer fire. Mindre enn ett minutt senere kuttet motor nummer to. I løpet av sekunder stanset også motor nummer en og tre.

Jumbojeten med 247 passasjerer om bord var dermed i glideflukt. Mannskapet varslet kontrollsentralen i Jakarta om nødssituasjonen.

Mens mange passasjerer satt med surstoffmasker på og skriblet sine siste hilsener til sine kjære, kom kaptein Eric Moody med en annonsering til passasjerene i en tone av klassisk britisk understatement:

«Ladies and gentlemen, this is your Captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them going again. I trust you are not in too much distress.»

Hedret

Etter hvert som flyet mistet høyde, klarte mannskapet å få liv i motorene igjen, og med sterkt redusert sikt gjennom de ødelagte vinduene i cockpit klarte de å lande i Jakarta. Vel nede på bakken hadde de imidlertid ingen mulighet til å se nok til å parkere den store maskinen, så de måtte taues til terminalen.

Etterforskningen viste at flyet hadde truffet aske fra et utbrudd av vulkanen Galunggung. Siden asken var tørr, var den ikke synlig på værradaren, som er laget for å påvise fuktighet i skyene.

Mannskapet ble senere hedret for sin innsats på Speedbird 9.

IslandVulkan_fint bilde  (Foto: Reuters)
IslandVulkan_fint bilde (Foto: Reuters)
Smoke  billows from an erupting volcano which seems to be close to the top of  the Eyjafjallajokull glacier on April 14, 2010 near Reykjavík. All London  flights, including those from Heathrow, will be suspended from noon (1100  GMT) today due to volcanic ash from Iceland that has already caused almost  300 cancellations here, officials said. AFP PHOTO/ICELANDIC COAST GUARD  (Foto: AFP/AFP)
Smoke billows from an erupting volcano which seems to be close to the top of the Eyjafjallajokull glacier on April 14, 2010 near Reykjavík. All London flights, including those from Heathrow, will be suspended from noon (1100 GMT) today due to volcanic ash from Iceland that has already caused almost 300 cancellations here, officials said. AFP PHOTO/ICELANDIC COAST GUARD (Foto: AFP/AFP)
In  this image made available by the Icelandic Coastguard, taken Wednesday  April 14, 2010, smoke and steam rises from the volcano under the Eyjafjallajokull  glacier in Iceland, which erupted for the second time in less than a  month, melting ice, shooting smoke and steam into the air and forcing  hundreds of people to flee rising floodwaters. Authorities evacuated  800 residents from around the glacier as rivers rose by up to 10 feet  (3 meters). Emergency officials and scientists said the eruption under  the ice cap was 10 to 20 times more powerful than one last month, and  carried a much greater risk of widespread flooding. (AP Photo/Icelandic  Coastguard, ho) ** EDITORIAL USE ONLY ** (Foto: AP/AP)
In this image made available by the Icelandic Coastguard, taken Wednesday April 14, 2010, smoke and steam rises from the volcano under the Eyjafjallajokull glacier in Iceland, which erupted for the second time in less than a month, melting ice, shooting smoke and steam into the air and forcing hundreds of people to flee rising floodwaters. Authorities evacuated 800 residents from around the glacier as rivers rose by up to 10 feet (3 meters). Emergency officials and scientists said the eruption under the ice cap was 10 to 20 times more powerful than one last month, and carried a much greater risk of widespread flooding. (AP Photo/Icelandic Coastguard, ho) ** EDITORIAL USE ONLY ** (Foto: AP/AP)
In  this image made available by the Icelandic Coastguard, taken, Wednesday  April 14, 2010, smoke and steam rises from the volcano under the Eyjafjallajokull  glacier in Iceland, which erupted for the second time in less than a  month, melting ice, shooting smoke and steam into the air and forcing  hundreds of people to flee rising floodwaters. Authorities evacuated  800 residents from around the glacier as rivers rose by up to 10 feet  (3 meters). Emergency officials (Foto: AP/AP)
In this image made available by the Icelandic Coastguard, taken, Wednesday April 14, 2010, smoke and steam rises from the volcano under the Eyjafjallajokull glacier in Iceland, which erupted for the second time in less than a month, melting ice, shooting smoke and steam into the air and forcing hundreds of people to flee rising floodwaters. Authorities evacuated 800 residents from around the glacier as rivers rose by up to 10 feet (3 meters). Emergency officials (Foto: AP/AP)
Smoke  billows from a volcano in Eyjafjallajokull April 14, 2010. A volcanic  eruption in Iceland spewed black smoke and white steam into the air on  Wednesday and partly melted a glacier, setting off a major flood that  threatened to damage roads and bridges. REUTERS/Ingolfur Juliusson (ICELAND    Tags: DISASTER ENVIRONMENT) (Foto: INGOLFUR JULIUSSON/Reuters)
Smoke billows from a volcano in Eyjafjallajokull April 14, 2010. A volcanic eruption in Iceland spewed black smoke and white steam into the air on Wednesday and partly melted a glacier, setting off a major flood that threatened to damage roads and bridges. REUTERS/Ingolfur Juliusson (ICELAND Tags: DISASTER ENVIRONMENT) (Foto: INGOLFUR JULIUSSON/Reuters)
In  this image made available by the Icelandic Coastguard taken Wednesday  April 14, 2010, smoke and steam rises from the volcano under the Eyjafjallajokull  glacier in Iceland, which erupted for the second time in less than a  month, melting ice, shooting smoke and steam into the air and forcing  hundreds of people to flee rising floodwaters. Authorities evacuated  800 residents from around the glacier as rivers rose by up to 10 feet  (3 meters). Emergency officials and scientists said the eruption under  the ice cap was 10 to 20 times more powerful than one last month, and  carried a much greater risk of widespread flooding.(AP Photo/Icelandic  Coastguard, ho) **EDITORIAL USE ONLY** (Foto: AP//Icelandic Coastguard/AP)
In this image made available by the Icelandic Coastguard taken Wednesday April 14, 2010, smoke and steam rises from the volcano under the Eyjafjallajokull glacier in Iceland, which erupted for the second time in less than a month, melting ice, shooting smoke and steam into the air and forcing hundreds of people to flee rising floodwaters. Authorities evacuated 800 residents from around the glacier as rivers rose by up to 10 feet (3 meters). Emergency officials and scientists said the eruption under the ice cap was 10 to 20 times more powerful than one last month, and carried a much greater risk of widespread flooding.(AP Photo/Icelandic Coastguard, ho) **EDITORIAL USE ONLY** (Foto: AP//Icelandic Coastguard/AP)
Røyk  og damp henger over vulkanen under isbreen Eyjafjallajökull på Island.  Vulkanen har hatt sitt andre utbrudd på under en måned. (Foto: Brynjar  Gauti/AP)
Røyk og damp henger over vulkanen under isbreen Eyjafjallajökull på Island. Vulkanen har hatt sitt andre utbrudd på under en måned. (Foto: Brynjar Gauti/AP)
The  last planes leave Heathrow Airport shortly before all flights in and  out of the UK are cancelled due to the dangers of volcanic ash blowing  south from Iceland. London, England   15.04.10 Credit Mandatory: WENN.com  (Foto: DSDD/ZOB/wenn.com)
The last planes leave Heathrow Airport shortly before all flights in and out of the UK are cancelled due to the dangers of volcanic ash blowing south from Iceland. London, England 15.04.10 Credit Mandatory: WENN.com (Foto: DSDD/ZOB/wenn.com)
An  aerial handout photo from the Icelandic Coast Guard shows Highway 1,  the road that goes around Iceland, cut off by a flood caused by a volcanic  eruption at Eyjafjalla Glacier April 14, 2010. The volcanic eruption  on Wednesday partially melted a glacier, setting off a major flood that  threatened to damage roads and bridges and forcing hundreds to evacuate  from a thinly populated area. Picture taken April 14, 2010. REUTERS/Icelandic  Coast Guard/Arni Saeberg/Handout (ICELAND   Tags: DISASTER) FOR EDITORIAL  USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS (Foto:  HO/REUTERS)
An aerial handout photo from the Icelandic Coast Guard shows Highway 1, the road that goes around Iceland, cut off by a flood caused by a volcanic eruption at Eyjafjalla Glacier April 14, 2010. The volcanic eruption on Wednesday partially melted a glacier, setting off a major flood that threatened to damage roads and bridges and forcing hundreds to evacuate from a thinly populated area. Picture taken April 14, 2010. REUTERS/Icelandic Coast Guard/Arni Saeberg/Handout (ICELAND Tags: DISASTER) FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS (Foto: HO/REUTERS)
An  aerial handout photo from the Icelandic Coast Guard shows flood caused  by a volcanic eruption at Eyjafjalla Glacier in southern Iceland April  14, 2010. The volcanic eruption on Wednesday partially melted a glacier,  setting off a major flood that threatened to damage roads and bridges  and forcing hundreds to evacuate from a thinly populated area. Picture  taken April 14, 2010. REUTERS/Icelandic Coast Guard/Arni Saeberg/Handout  (ICELAND   Tags: DISASTER) FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING  OR ADVERTISING CAMPAIGNS (Foto: HO/REUTERS)
An aerial handout photo from the Icelandic Coast Guard shows flood caused by a volcanic eruption at Eyjafjalla Glacier in southern Iceland April 14, 2010. The volcanic eruption on Wednesday partially melted a glacier, setting off a major flood that threatened to damage roads and bridges and forcing hundreds to evacuate from a thinly populated area. Picture taken April 14, 2010. REUTERS/Icelandic Coast Guard/Arni Saeberg/Handout (ICELAND Tags: DISASTER) FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS (Foto: HO/REUTERS)
Vulkantomflyplass  (Foto: Kirsty Wigglesworth/AP)
Vulkantomflyplass (Foto: Kirsty Wigglesworth/AP)