a briefing from the Civil Aviation Authority - 14 May 2010
On 20th March 2010 the Icelandic volcano Eyjafjallajökul
began erupting for the first time in 190 years, sending a
cloud of ash over Northern Europe. Volcanic ash is a known
hazard to aircraft, and the unequivocal guidance from the
International Civil Aviation Organisation (ICAO) - based on
such events as the multiple engine failure that affected a
British Airways flight over Indonesia in 1982 - is that aircraft
encountering volcanic ash must avoid it completely. The
ICAO guidance, which is based on the evidence from a
number of previous volcanic events, states simply that
operators should AVOID, AVOID, AVOID.
Volcanoes erupt frequently, but normally only affect areas
where air traffic is light and airspace is uncongested. Their
ash clouds are tracked by nine global Volcanic Ash Advisory
Centres, which provide information to allow flights to
reroute their flight paths around any area of contamination.
Satellite Image of the ash plume on 19 April 2010. Source Met Office
The disruption to UK flights on 15 April and the five days that followed was caused by unprecedented conditions
- frequent eruptions from Eyjafjallajökul combining with a weather pattern that sent volcanic ash into airspace
where there was simply not the room to avoid it. As the severity of the situation increased UK air traffic control
service provider NATS announced it would not provide IFR clearances into the contaminated airspace in
accordance with International Civil Aviation Organisation (ICAO). As such, no flights could take place in the UK’s
Controlled Airspace. At this stage given the ICAO guidance documentation, there was no alternative strategy
that would have allowed NATS or the CAA to provide the necessary assurance of safety.
The UK was not alone in restricting flight operations, with many other European countries following suit as the
ash cloud drifted into their airspace.
Safety always comes first in aviation. The UK has one
Aircraft with special instruments to measure the ash
of the world's best safety records, secured by strict
cloud’s density were used, complementing the data
guidelines. When the scale of the problem and extent of
provided by six ground-based lasers located across the
airspace closures became evident on 15 April, and
UK. Over the course of the first weekend further
looked set to continue for some time, the challenge
evidence was gathered from commercial jets, without
facing the CAA was evident. It had to establish whether
passengers, flying a flight path behind the instrument-
the guidelines from ICAO could safely be revised to
bearing aircraft. Before and after any flights, engines
allow aircraft to fly through a low density of ash (instead
were intensively examined to check for any correlation
of the zero tolerance specified which was not based on
between ash density and engine damage. Meanwhile,
hard scientific evidence) and to better understand and
work was underway with manufacturers to frame new
predict the height and density of ash contamination in
guidance for allowing aircraft to safely fly through
How was the new level set?
The scale of the challenge was enormous. International
European controlled airspace, imposed a further 60 nautical
and European regulators, manufacturers and aviation
mile buffer around the no-fly zone as a contingency
experts had to co-ordinate their expertise and agree a new
measure, in place until there was evidence in place to show
zoning system for the airspace affected by volcanic ash
the buffer was unnecessary.
and to establish new airworthiness guidance. The CAA,
with NATS, took the lead in getting both of these
Since then airline operations have resumed without
workstreams underway, and after five days of intensive
major incident, or any reports of airframe or engine
conference calls with hundreds of experts the necessary
damage. There have been cases of aircraft encountering
data was amassed for the basis of the agreed new
some suspected ash and ash deposits have been
guidelines. Politicians, airlines and tour operators were
discovered on aircraft after a flight. This is to be expected
kept abreast of developments.
as the ash cloud has not gone away and therefore aircraft
will be encountering ash as they fly through it.
On Monday 19 April, Europe agreed a proposed new
zoning system for allowing flights to operate in low levels
The no fly zone has since affected parts of the UK a
of ash. This established a no-fly zone where the predicted
number of times, but relatively small areas and for much
ash density exceeded the proposed ash tolerance figure.
shorter periods of time. Transatlantic flights have been
This however proceeded any final approval from
disrupted, most significantly over the weekend of 8/9 May
manufacturers to allow flights in any amount of ash. This
when a large no fly zone was put in place to the west of
allowed identification of a secondary zone where flying
Ireland. Spanish airspace has also been affected, causing a
could be resumed, albeit subject to some additional
lot of disruption to flights in and out of Spain.
inspections of the aircraft if evidence of ash contamination
Maximising safe flying is the objective of all involved. As
was found and a tertiary, ash-free zone where normal
such the CAA is constantly reviewing the measures in
operations could be conducted.
place and, based on the evidence of the flights that have
By the afternoon of Tuesday 20 April, key manufacturers
taken place so far around the ash, the CAA decided on 10
had provided the CAA with agreed revised guidelines which
May to remove the requirement for a 60 nautical mile
would not compromise safety. This resulted in the
buffer around the area of higher ash concentration. This
manufacturers setting an agreed limit of low levels of ash
has been welcomed by industry and it is expected that the
that were deemed to be safe. Forty-five minutes after
rest of Europe, once they have completed their own
securing that agreement, the CAA board met in emergency
checks, will make the same judgement.
session and agreed the new guidelines. Two hours after the
meeting, the skies reopened and the first flights landed at
Heathrow – three of them reporting smells of sulphur – an
indication that they had flown through, or near to areas of ash
contamination. The new limit of tolerable ash density is set at
2X10-3 grammes of ash per cubic metre of air.
This meant that no fly zones were established where
the ash had a higher concentration than that agreed as
being safe by the manufacturers, the secondary zone was
where ash was present but at lower concentrations (down
to an ash density of 2X10-4 grammes of ash per cubic
metre of air) so aircraft were allowed to fly with additional
safety measures and a strict inspection regime in place, and
a tertiary ash free zone (below 2X10-4 grammes of ash per
cubic metre of air) where aircraft could continue operations
as normal. Eurocontrol, the air traffic provider for much of
Illustrative Met Office modelled ash concentration chart from 05 May 2010
What happens now?
Eyjafjallajökul is continuing to erupt. Airlines are
conjunction with airlines, to build the evidence for
examining aircraft engines and airframes before and
new technical guidelines.
after flights, including assessing the effects of
cumulative exposure to ash. Scientists are constantly
Manufacturers can perform testing based on ash
monitoring the ash cloud’s movements.
intake into engines and certify its effect on airframes
and instrumentation, and would be responsible for
As the UK has some of the most congested skies in the
making any changes to technical guidelines.
world, no fly zones will continue to disrupt UK flights
until the volcano stops emitting large volumes of ash,
Throughout this process, the CAA will ensure that the
the weather patterns change or the aviation industry
public is at the heart of all our work, and our goal will
comes up with technical solutions to allow aircraft
be to allow as much flying as safely possible, working
engines to fly through denser levels of volcanic ash.
with all stakeholders to be sure that safety is not
compromised and disruption is minimised.
As the volcano and the weather are out of our control,
the emphasis of the CAA’s future is on working with
industry and other partners on continuing to improve
the airworthiness solution.
The CAA is also continuing to drive activities across
Europe to develop more detailed scientific
understanding of the problem. As the aviation sector’s
UK regulator, we are working hard to bring the
industry together to address the issue. We are
continuing to provide expert guidance, and are looking
to engine and aircraft manufacturers, working in
Timeline of events
Saturday 20 March
unsafe for flights.
allows Manchester to open briefly.
Icelandic volcano Eyjafjallajökull
CAA starts internal briefings on
CAA, NATS, and Met Office in
begins erupting for the first time in
contact with Eurocontrol. CAA
meets Transport Secretary and
NATS announces that from 1200
agrees further updates and
Wednesday 14 April
until at least 1800, it will not
briefings throughout the day,
provide IFR clearances into the
More forceful eruption, emitting
including afternoon meeting with
contaminated airspace in
plumes of ash.
airline & BAA representatives.
accordance with International
Regular contact continues
CAA is informed & advice is
Civil Aviation Organisation (ICAO)
throughout the period.
provided to airlines.
guidance that flying should not
take place where there is ash in
CAA establishes international
Late evening, as the extent of the
the atmosphere. CAA follows this
teleconference call, drawing
ash cloud emitted become
with a NOTAM reenforcing the
together almost 100 organisations
apparent, the National Airspace
decision with advice to VFR pilots.
to assess whether slightly denser
Crisis Management Executive
contamination than the current
(NACME) convenes, sponsored by
Six ground based LIDAR (Light
ICAO level would be an acceptable
CAA’s DAP, including CAA’s SRG,
Detection and Ranging) radars
risk based position.
MoD, NATS, DfT and others.
detect ash in the atmosphere.
Thereafter NACME meets up to
Dornier 228 aircraft launched for
Dornier instrumented aircraft from
three times daily throughout the
NERC deployed to verify Met Office
Friday 16 April
Thursday 15 April
Volcanic activity intensifies with ash
Evidence of ash presence
up to 30,000ft.
Early morning, the ash cloud
detected at various locations
reaches Scottish airspace making it
throughout UK. Small window
Continued on back page
CAA timeline of events
• a no fly zone within 60 nautical
reduce risk based around continued
Saturday 17 April
miles of the higher ash density area;
serviceability of engines and
airframes between flights, and
First International Teleconference
• a second zone where flying will
requiring airlines to conduct their
chaired by CAA with International
not in principle be impeded (subject
own safety risk assesments.
Airframe and Engine Manufacturers,
to agreed risk assessments and
Service Providers, Operators,
measures) even though some ash is
• Instrumented flights to continue to
Specialist Meteorological, Research
present and where the decisions
check on density.
and Geological Agencies and with
about operations will be taken by
European and International Aviation
• Use banding model delineated by
• a third zone which is not affected
There is no positive prognosis for
CAA briefs Transport Secretary and
allowing flights to recommence due
airlines on Board decision,
to further eruptions, settled weather
Eurocontrol Press conference
distributes position statement to
patterns and N/NW winds.
announces new zoning to take
International Teleconference Group
effect 0600 20 April.
and makes press announcement
Operator in Penzance detects ash
that airspace will be reopened at
on airframe on landing. Similar
Third International Teleconference.
reports from MoD in West Wales
Data examined from further
and North England.
instrumented Dornier flights which
Nine engine manufacturers go
show low level contamination. Still
public with support for new safety
Throughout weekend LIDAR data
no uniform agreement from engine
scrutinised – all showing continuing
manufacturers about changing the
mild presence of contamination.
3 - 5 May
Sunday 18 April
Ash plume returns to cover parts of
UK FIR open for overflight, above
UK airspace at levels above the
Second International Teleconference
area of volcanic ash, above FL200.
2X10-3 g per cubic metre threshold
call. More data is requested by
Tuesday 20 April
for several days, resulting in airports
engine manufacturers on likely
being closed in Scotland and
levels of contamination.
At morning meeting with Transport
Secretary, airlines, tour operators
Instrumented Dornier flight ahead
8 - 10 May
and NATS, CAA updates on
of BA flight, to measure
contamination levels and practical
progress towards a solution,
High concentrations of ash in
explains evidence base and informs
airspace over parts of south west,
all that CAA Board is on standby for
southern and central Europe lead to
Overflight policy circulated. Leads
to proposals as announced at
Monday 10 May
Eurocontrol conference 10.00am
Fourth International Teleconference
CAA announces that the 60nm
Monday 19 April
CAA Emergency Board meeting
buffer zone in place around areas of
held at 17.30 and agrees way
high ash concentrations can safely
CAA work continues to seek
be removed following two more
agreement from aircraft engine
weeks of examination of the data,
manufacturers - overnight work in
• 2X10-3 g of ash per cubic metre of
thereby safely reducing the
US suggests a solution may be
air set as an acceptable safety limit.
maximum extent of the no fly zone
around areas of higher ash density.
• Requirements to be placed on
European Transport Ministers meet
Aircraft Operators, Air Navigation
and agree a three band model
Service Providers and Aerodromes;
including range of inspections to
More information about volcanic ash, the monitoring of ash flows, and the authorities’ response can be found
from the following websites:
The CAA - www.caa.co.uk
The UK Met Office - www.metoffice.gov.uk
NATS - www.nats.co.uk
The British Geological Survey - www.bgs.ac.uk