Coming to terms with the ash cloud

February 2, 2011

A 2000ft plume of volcanic ash from Iceland's Eyjafjallajökull brought chaos and confusion to European airspace last year. North Sea offshore helicopter operators are accustomed to dealing high winds, driving rain and freezing fog, but how did they cope with this new phenomenon?

Aviators were warned by the UK Met Office on 14 April 2010 that an ash cloud had the 'potential' to impact some areas, but no-one was prepared for what was about to unfold. As the ash cloud began to spread from the Icelandic volcano it quickly emerged that the rich volcanic magma contained high levels of gas and silica.

Offshore personnel disembarking from a CHC EC 225 on the Bredford Dolphin semisubmersible drilling rig.

This composition interacted with the thick ice around Eyjafjallajökull's glacier causing a massive second explosion, the result of which was an unusually fine silicate ash which remained in the air currents for far longer than regular volcanic ash. Indeed the ash lingered for up to eight days compared to the 36 hours historical data predicted, allowing considerable time for the cloud to spread. Whilst computer modelling was available for certain volcanic eruptions, this was something entirely new.

Among those affected was leading North Sea helicopter operator CHC. 'The response from the International Civil Aviation Organisation (ICAO) was clear. with a recommendation that flight through the ash must be avoided,' recalls Peter Walmsley, manager flight operations at CHC Aberdeen. 'Immediately all eyes were on satellite and Light Detection and Ranging (Lidar) evidence to monitor and track the ash cloud as it moved over the UK and the UK's Civil Aviation Authority took the decision to close its airspace.

With offshore air services suspended and thousands of offshore personnel stranded, the industry went into overdrive evaluating all the data it could gather in order to find out how it could keep operating.

'When it became apparent that we could operate tactically by flying through ash-free zones, with the CAA's agreement services recommenced but we were always working in six-hour windows,' says Walmsley. 'The rules changed almost every day due to the pressure from industry, but what was clear was we needed thorough risk assessment sessions and new guidance documents, ER procedures and full maintenance inspection regimes for flight crews and engineers.

'No-one had ever experienced this type of situation before so co-operation with the aircraft manufacturers was a must to ensure safety at all times. Aircraft were shutdown between flights and full inspections carried out.

'With flights operating in clear areas and forecasts improving, the industry set up a 60 nautical mile buffer zone around the boundary of the ash cloud and, later, a no-fly zone in any area with an ash concentration of 2 x 10-3g/m3.

'The ash was too small to be stopped by filters and was not immediately visible to flight crews so we really had to rely on our predictions,' Walmsley explains. 'While there was ash present in the atmosphere, the effect it had on the aircraft was that we were seeing incredibly clean engine compressors and turbine blades as the ash was having a sandblasting effect. We don't yet know the long-term effect this will have on the life of these engines and maintenance programmes will be ongoing for many years to come to monitor the situation.'

On 25 May, news agencies reported that Eyjafjallajökull was no longer emitting ash. In July, the ICAO published new contingency plans, EUR Doc 019/ Nat Doc 006 Part II, which established recommended actions for all parties and confirmed the now internationally accepted ash concentration levels.

The UK's CAA also set medium contamination zones for the existing North Sea fleet based on time limitations, with all new aircraft now required to comply to an ash contamination certification process.

'A year ago none of us would ever have expected that we would have become volcano experts, but in less than eight months the industry radically changed the boundaries of what it is able to cope with,' notes Walmsley. 'New manufacturer approvals and specialised maintenance procedures are in place, operations manuals have been updated, risk assessments carried out and flight procedures established and proven.

'It may seem like the situation we experienced last April was a one off and unlikely to be seen again, but there are many volcanoes on Earth that are moderately active so this may not be the last time we encounter an ash cloud.

'However, if and when it happens the industry will be better prepared.' OE

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