International Civil Aviation Organization
IAVWOPSG/3-WP/11
5/02/07
WORKING PAPER
INTERNATIONAL AIRWAYS VOLCANO WATCH OPERATIONS GROUP
(IAVWOPSG)
THIRD MEETING
Bangkok, Thailand, 19 to 23 March 2007
Agenda Item 5: Operation of the IAVWOPSG
5.3: Assessment of the use of the smell of sulphur as an indicator of the presence of
volcanic ash in the atmosphere
REPORT ON THE USE OF THE SMELL OF SULPHUR AS AN INDICATOR OF
THE PRESENCE OF VOLCANIC ASH IN THE ATMOSPHERE
(Presented by Rapporteur)
SUMMARY
Volcanoes are the only significant source of large quantities of sulphur dioxide
(SO2) gas at jet-cruising altitudes. Therefore, SO2 detected by the flight crew at
cruise altitude is almost certainly associated with volcanic activity and may indicate
that an ash cloud is present or nearby. Further study is required on how to report
detection of SO2 on the flight deck. In addition, it is believed that there is a short
fall in training with regard to SO2. Flight crews need to be trained on the detection
of SO2 and understand the procedures to be followed upon detection of SO2. To
help air carriers develop appropriate training material the International Airways
Volcano Watch Operations Group should consider enhancing existing training
material that is currently available to air carriers to train their flight crews.
1.
INTRODUCTION
1.1
At the International Airways Volcano Watch Operations Group/2 meeting in Lima in
2005, conclusion 2/7 established an ad hoc working group to assess the use of smell of sulphur as an
indicator of the presence of volcanic ash in the atmosphere. This paper is presentation of the discussion
among the members of the ad hoc group with a proposed recommendation on how to proceed.
(4 pages)
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2.
2.1
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DISCUSSION
Smell of sulphur as an indicator of the presence of volcanic ash in the atmosphere
2.1.1
Explosive magmatic eruptions produce columns of gases and particles (ash) that may
reach up to stratospheric altitudes, and such eruptions always emit sulphur in the form of sulphur dioxide
(SO2) gas. Larger ash particles immediately begin to fall out from the column, leaving finer ash and
gases such as SO2 suspended in the atmosphere. The ash and gas plume detaches from the volcanic vent
to form a drifting volcanic cloud. In the presence of strong wind shear, fallout of ash particles at lower
altitudes may form a separate, short-lived cloud dominated by ash that drifts in a different direction to the
higher-altitude SO2-rich cloud. Very fine ash in drifting volcanic clouds is difficult to detect by satellite
remote sensing after the first day or so of atmospheric residence, but SO2 remains as a marker owing to
its long lifetime at high altitudes. Over days to weeks, the SO2 converts to sulphate aerosol.
2.1.2
Volcanoes also emit sulphur gases (mainly SO2) into the lower troposphere below ~5 km
(16,000 ft) by pre-eruptive degassing or during basaltic effusive eruptions such as in the Galapagos
Islands and Hawaii. These emissions typically are ash-poor or ash-free, although acid aerosol will be
present. On occasions in the tropics, lower tropospheric SO2 can be lofted to jet cruising altitudes by
strong convective meteorological systems.
2.1.3
Volcanoes are the only significant source of large quantities of sulphur gases at jetcruising altitudes. Hence, any SO2 odor (acrid, like electrical smoke) detected by flight crew at such
altitudes is almost certainly associated with volcanic activity and indicates the possibility that some ash
may be present or nearby.
2.1.4
At the IAVWOPSG/2 Meeting it was noted that SO2 detected on the flight deck is most
likely attributed to volcanic activity and that this information needs to be reported to an Area Control
Center so the information can be forwarded to the appropriate Volcanic Ash Advisory Center for further
evaluation. It was also noted further work was necessary concerning the use of the smell of sulphur as a
tool for the detection of volcanic ash. In Amendment 74 to Annex 3 a proposal was made to issue a
Special AIREP for SO2. Four States commented that it seems premature to issue a Special AIREP and
indicated uncertainty about whether the issuance of a Special AIREP is the appropriate course of action.
The Secretary agreed in the response to the comments that further evaluation is required.
2.1.5
The issue of providing a Special AIREP for SO2 or issuing the existing Special AIREP
for VA, if SO2 is detected, needs to be discussed further in relation to the tangible information that would
be provided to the pilot and dispatcher. One of the significant short falls in the IAVW program is the
dissemination and communication of information. Recently the ICAO CAR/SAM, EUR, and ASIA/PAC
Regions conducted communication tests on the issuance of WV and VA NOTAMS. Special AIREPS for
VA were not part of this test protocol. The airlines and Air Traffic Services are depending more and
more on the datalinking of information between the flight deck and ground control. There are fewer
manual reports as automation becomes the principal means of relaying data and information for
temperature, wind, water vapor, and turbulence. Many Special AIREPs are not distributed by Air Traffic
Service Units and therefore adding an AIREP for SO2 may not resolve the short fall in detecting the
existence and location of volcanic ash cloud that is unreported. Nevertheless, from the VAAC viewpoint
there is an operational need for these reports and to provide this information would have to be done
manually until there is a means to automate the reporting of this phenomenon.
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2.2
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Development of guidance material for pilots
2.2.1
Flight crews need to be trained to understand that SO2 indicates the possibility of
volcanic ash in the vicinity of their route and that on-board weather radar cannot detect volcanic ash
clouds. The basic indicators that have been provided to flight crews that an aircraft may have entered an
ash cloud are: (1) smoke or very fine dust in cabin, (2) acrid odor, (3) low airspeed indications, (4) cargo
fire warning (caused by volcanic ash triggering smoke detectors), (5) static discharges (St. Elmo’s fire)
around windscreen or on wing stabilizer fin tips, (6) white glow (searchlight effect) shining out of engine
inlets, and (7) multiple engine malfunctions (increasing EGT, power loss, stall, or flame out). None of
these indicators provide any guidance on SO2 except for the item identified as acrid odor.
2.2.2
Moreover, when SO2 is detected procedures need to be developed in consultation with
aviation medical authorities. Procedures or guidance material that is developed needs to consider issues
associated with the protection of the flight crew to ensure they maintain control of the aircraft. Some
airlines already have procedures in place that address situations that are to be followed for odors.
Whether this procedure is appropriate for SO2 needs to be evaluated. Guidance material also has to
consider the health physics on what is the best practice to detect and report SO2 while en route. While it
is considered that the human nose is good gauge on judging whether there is SO2 presence it may not be
able to distinguish between the intensity levels and the associated hazard of an ash cloud. Moreover the
human nose is quickly desensitized after the initial smell of SO2.
2.2.3
Even though information has been provided in the ICAO Manual on Volcanic Ash,
Radioactive Material and Toxic Chemical Clouds (Doc 9691) on how to detect volcanic ash it is not
believed that most pilots are fully trained on this hazard. A review of existing available information has
revealed that Airbus does have material available to airlines to assist in training. Even though this
information is readily available a quick survey of how many airlines actually make use of this information
provided a mix set of results. Some airlines do provide training with regard to volcanic ash there are other
airlines that do not have adequate training. While additional guidance material would help supplement
existing training material available to air carriers, further assessment needs to be done on how to ensure
that air carriers are providing appropriate training material for flight crews.
2.3
conclusion:
In accordance with the discussion above the group may wish to formulate the following
Conclusion 3/.. ―
Evaluation of the appropriate notification when
sulphur is detected by the flight crew at cruise
altitude
That, the current ad hoc working group assessing the smell of sulphur as
an indicator of the presence of volcanic ash in the atmosphere shall be
tasked to continue their work to:
a)
assess how a message that provides information only on smell of
sulphur would be used in operations by area control centres, airline
operations, and meteorological watch offices; and
b)
develop draft guidance for review by the IAVWOPSG/4 Meeting
for inclusion in Doc 9766, Handbook on the International Airways
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Volcano Watch (IAVW) — Operational Procedures and Contact
List.
3.
3.1
ACTION BY THE IAVWOPSG
The IAVWOPSG is invited to:
a) note the information in this paper; and
b) decide on the draft conclusion proposed for the group’s consideration.
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