Volcanic ash in the atmosphere may pose a
serious hazard to aircraft in flight. That is why the aircraft should avoid
volcanic ash encounters. It comprises minerals unique to the volcanic eruption.
Minerals common to most volcanic ash are silica together with smaller amounts
of the oxides of aluminum, iron, calcium, and sodium. The glassy silicate
material is hard and extremely abrasive. Its melting point is below jet engine burner
temperature that introducing additional hazards.
Furthermore, a volcanic ash cloud may be
accompanied by gaseous solutions of sulfur dioxide (when combined with water
create sulphuric acid), chlorine (when combined with water create hydrochloric
acid), and other chemicals which are corrosive to the airframe and are
hazardous to health.
Another term you may need to know it, the
volcanic cloud, which is the sum of the material ejected from a volcano into
the atmosphere and transported by winds aloft. It comprises volcanic ash,
gases, and chemicals.
Before I go deeper by my explanation, you
need to have an idea about the following two terms:
Affected area : A volume of airspace, an aerodrome, or
another area on the ground, identified by VAA / VAG and/or SIGMET
as being affected by known or forecast volcanic cloud contamination. Note : VAA - Volcanic Ash Advisory VAG - Volcanic Ash Advisory in graphical form SIGMET- information concerning en-route weather phenomena
which may affect the safety of aircraft operations. Danger area : A volume of airspace identified by NOTAM as
being affected by levels of known or forecast volcanic cloud contamination
which States judge merit publication to operators. Note : NOTAM - A notice distributed through telecommunication
containing information concerning the establishment, condition, or change in
any aeronautical facility, service, procedure, or hazard, the timely knowledge
of which is essential to personnel concerned with flight operations. It is easy to imagine the hazard that
volcanic ash poses to an aircraft that encounters it in the atmosphere. The
effects are: Volcanic ash mixtures are introduced
through the fans. Three effects contribute to the overall engine damage. It is the most critical, is the fact that
volcanic ash has a melting point below jet engine operating temperatures with
thrust settings above idle. The ash melts in the hot section of the engine and
fuses on the high-pressure nozzle guide vanes and turbine blades. This
drastically reduces the high-pressure turbine inlet guide-vane throat area
causing the static burner pressure and compressor discharge pressure to
increase rapidly which, in turn, causes engine surge. This effect alone can
cause immediate thrust loss and possible engine flame-out.
The volcanic ash being abrasive also erodes
compressor rotor paths and rotor blade tips (mostly high-pressure section),
causing loss of high-pressure turbine efficiency and engine thrust. The erosion
also results in a decrease in the engine stall margin. The ash can clog flow holes in the fuel and
cooling systems. Such a condition would render engine restart very difficult. In addition to engine abrasion, volcanic
ash abrades cockpit windows, the leading edges of the flight surfaces, and the
tailfin and can "sandblast" the paint from the airframe. Any parts
protruding from the airframes such as antennas, probes, ice detectors, and
angle of attack vanes can be damaged and may be rendered inoperable. From the
safety standpoint, the abrasion of the cockpit windows reduces the cockpit crew
forward visibility and can present a serious problem during landing. Damage to
the antennas can lead to a complete loss of high frequency (HF) communications
and a degradation of very high frequency (VHF) communications. Damage to the
various sensors can seriously degrade the information available to the pilot
through the cockpit instruments. Thus, rendering control of the aircraft
difficult. Note : British Airways B747 made an emergency
landing at Jakarta in 1982 following its encounter with volcanic ash. There have been no known crashes as a
result of volcanic ash ingestion. A total of 253 encounters with volcanic ash
or gas clouds between 1953 and 2016 were identified, of which 122 occurred in
the period 2010-2016. Significant effects worth mentioning include: - blocked pitot tubes - replacement of damaged engines - multiple engine failure - electrical and computer failure - physical restrictions (breathing, speech,
nausea, eye irritation) Volcanic ash poses to aircraft, like with
most threats in aviation, the best course of action is to avoid it in the first
place. As part of the preflight planning, if a
flight is going to fly through an area that could be affected by volcanic
ash. Airline flight planners can adapt
the route to avoid the worst of it. Volcanic ash damaged the jet turbine
engines, abrades cockpit windows, airframe, and flight surfaces, clogs the
pitot-static system, penetrates air conditioning and equipment cooling systems,
and contaminates electrical and avionics units, fuel and hydraulic systems, and
cargo-hold smoke-detection systems. The references used in writing this article
are: 1-
ICAO DOC 9974, Flight Safety and Volcanic Ash, Risk management of flight
operations with known or forecast volcanic ash contamination. 2-
ICAO DOC 9691, Manual on Volcanic Ash, Radioactive Material and Toxic
Chemical Clouds. 3-
German Aerospace Center (DLR), Flying into Volcanic Ash Clouds: An
Evaluation of Hazard Potential.Effect of Volcanic Ash on Aircraft
1-
Effect on Jet Engines
The first (see number 1
in the below image)
The second (see number 2
in the below image)
The third
2- Effect on Airframe and Equipment
Now, you may ask, is there any aircraft
accident due to flying aircraft through volcanic ash or ash clouds?
Summary