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On the flight to Sweden, in a moonless and cloudless sky at 0508 GMT on February 28, 2000, scientists onboard the DC-8 monitoring sensitive research instruments reported a sudden increase in measurements that indicated the presence of a volcanic ash cloud. The onboard sensor data is presented in figures below showing measurements of sulfur dioxide (SO2) concentration in parts per trillion by volume (pptv), and figure 7(b) showing aerosol data for the seven-minute encounter. This encounter was more than 200 mi north of the predicted maximum northerly extent of the plume and approximately 800 nmi from the volcano (fig. 6). The volcanic plume was about 35 hr old at this time.
The principal damage sustained by aircraft flying into a volcanic ash cloud is abrasion to forward-facing surfaces, such as the windshield and leading edges of the wings, and accumulation of ash into surface openings, including engines. Abrasion of windshields and landing lights will reduce visibility forcing pilots to rely on their instruments. However, some instruments may provide incorrect readings as sensors (e.g., Pitot tubes) can become blocked with ash. Ingestion of ash into engines causes abrasion damage to compressor fan blades. The ash erodes sharp blades in the compressor, reducing its efficiency. The ash melts in the combustion chamber to form molten glass. The ash then solidifies on turbine blades, blocking air flow and causing the engine to stall.
The composition of most ash is such that its melting temperature is within the operating temperature (>1000°C) of modern large jet engines. The degree of impact depends upon the concentration of ash in the plume, the length of time the aircraft spends within the plume and the actions taken by the pilots. Critically, melting of ash, particularly volcanic glass, can result in accumulation of re-solidified ash on turbine nozzle guide vanes, resulting in compressor stall and complete loss of engine thrust. The standard procedure of the engine control system when it detects a possible stall is to increase power which would exacerbate the problem. It is recommended that pilots reduce engine power and quickly exit the cloud by performing a descending 180° turn. Volcanic gases, which are present within ash clouds, can also cause damage to engines and acrylic windshields, although this damage may not surface for many years.
In the past 30 years, more than 90 jet-powered commercial airplanes have encountered clouds of volcanic ash and suffered damage as a result. The increased availability of satellites and the technology to transform satellite data into useful information for operators have reduced the number of volcanic ash encounters. However, further coordination and cooperation, including linking operators and their dispatchers to the network of government volcano observers, is required throughout the industry. Boeing has always advocated that flight crews avoid volcanic ash clouds or exit them immediately if an encounter occurs. The company also recommends specific procedures for flight crews to follow if they cannot avoid an encounter.
Flight crews will be better prepared to avoid volcanic ash clouds and take the appropriate actions during an encounter if they understand the following information:
Volcanic Ash encounter can result in engine damage and malfunction:
Engine Malfunction. The principal risk to continued safe flight, arising from flight through high concentrations of volcanic ash, is the melting within the engine of ash particles, which are predominantly composed of silicates with a melting point of 1100°C. This melting point is considerably less than the core operating temperature of high by pass turbine engines which, at normal thrust settings, is at least 1400°C; there will be a trend for the core temperature to increase as engine design focuses on improved specific fuel consumption. Ingested silicate ash melts in the hot section of the engine and then fuses onto the high pressure turbine blades and guide vanes. This drastically reduces the throat area and both static burner and compressor discharge pressures rapidly increase and cause engine surge. Transient and possibly terminal loss of thrust can occur in the most severe cases with a successful engine re-start only possible if clear air can be regained. If present at sufficient densities, ash particles can also contribute to engine malfunction by simple deposition. In either case, the added debris clogs up the engine airflow and is likely to initially lead to engine surging and ultimately to a Flame Out. Reducing the thrust setting quickly to idle may lower the core temperature enough to prevent silicates melting.
Long Term Engine Damage. The abrasive effect of volcanic ash particle impact can cause surface roughness inside turbine engines which, whilst it will not affect their continued normal operation, will result in a reduced specific fuel consumption. It is impossible to repair such damage, so the life of an affected engine could be considerably reduced.
External Surface Corrosion. Ash can cause significant damage to the exposed surface of the aircraft skin and to the outer ply of windscreens. If the ash encounter is severe, the latter may become sufficiently abraded to be difficult to see through.
More on Volcanic ash and Aviation safety on Skybrary
The ash plume from Iceland has grounded planes for good reason – it wrecks jet engines, and it's at the right height to do so
Passengers stranded at UK airports after Icelandic volvano eruption halts air traffic Link to this video
Aircraft avoid any airspace that has volcanic ash in it for a simple reason: the ash can wreck the function of propeller or jet aircraft, because it is so fine that it will invade the spaces between rotating machinery and jam it – the silica melts at about 1,100C and fuses on to the turbine blades and nozzle guide vanes (another part of the turbine assembly), which in modern aircraft operate at 1,400C.
That, in turn, can be catastrophic – as the crew of two aircraft, including a British Airways Boeing 747, discovered in 1982 when they flew through an ash cloud from the Galunggung volcano in Indonesia. On both planes, all four engines stopped; they dived from 36,000ft (11km) to 12,000ft before they could restart them and make emergency landings.
That's not the only problem. Ash can pit the windscreens of the pilot's cabin, damage the fuselage and light covers, and even coat the plane so much that it becomes tail-heavy. At runways, ash creates an extra problem because takeoffs and landings will throw it into the air again – where the engines can suck it in and it will create horrific damage to moving parts that suddenly find themselves in contact.
The Icelandic plume has been thrown to between 6km and 11km into the atmosphere – exactly the height that aircraft would be flying.
Passengers on the BA flight that hit the cloud in 1982 said the engines looked unusually bright: soon after all four flamed out. "I don't believe it – all four engines have failed!" said the flight engineer. The crew were prepared to ditch, and the captain told the passengers: "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 under control. I trust you are not in too much distress."
Luckily, three of the engines could be restarted. The plane landed safely, and nobody was injured.
The problem with such ash is that it is extremely fine – less than 2mm in diameter, and in the case of fine ash only 6 microns in diameter – which means that it is easily carried by the wind; and because it is ejected by enormously hot air from a volcano it will often be thrown high into the jetstream at exactly the height that aircraft like to fly. The ash particles' light weight means that they will then remain there, dispersing so slowly it can take two to three years for them to vanish.
The measures taken today – clearing UK airspace from noon until at least 6pm – are a precaution, but a sensible one. Once ash has got into an engine, it is all but impossible to remove because it is so fine; no amount of washing will get every piece out. It pollutes filtration systems, electrical and avionic units – and the accompanying sulphuric acid aerosol can eat into rubber parts.
In all, more than 60 planes have been written off by ash damage. The US National Oceanic and Atmospheric Administration put the benefit to aviation of better avoidance of volcanic ash at around $58m annually.
This module is the third in the four-part Volcanic Ash series. It provides information on the impacts of an explosive volcanic eruption to aviation, climate, maritime operations and society. The threats, or impacts, from an eruption vary depending on the eruption style, duration and proximity--both in distance and altitude--to the volcano. As you learned earlier, an eruption may bring multiple hazards to urban and rural areas through:
Lahars (mudflows) and floods
Lava-flow inundation
Pyroclastic flows and surge
Volcanic ash and bomb fallout
Volcanic gases
In this module, we'll take a closer look at the impacts that volcanic eruptions, ash, and gases have on:
Aviation
Climate
Maritime operations
Society
Other environmental threats
Seaquake / Tsunami
Earthquake
Tokyo earthquake hit as plane was on runway: pilot tells what it was like
A commercial airline pilot tells what it felt like in his plane as the magnitude 9.0 earthquake hit in Japan at 5pm on March 11th.
"I was taxi-ing out for departure from Narita to Fukuoka, with a full load of passengers, after push back when I noticed something was wrong with the nosewheel steering - well that's what I thought the problem was," he wrote.
"The plane wanted to move across to the right side of the taxiway, and I had to use the tiller to try to bring it back, then it wanted to move quickly over to the left side, so I decided to stop, and return to the gate to get the steering checked out.
That was when ATC announced "Jishin, jishin! [Earthquake, earthquake!] All aircraft stop in present position. Earthquake."
"I stopped and set the parking brake, then the whole aircraft began to roll and shake so forcefully. It was lucky everybody was seated with their seatbelts fastened, it was like an amusement park ride."
The pilot said he requested permission from the airline to taxi back to the gate to offload passengers, but received no answer.
Eventually, when he raised someone on the ground, they told him not to move the plane, as passengers and staff had spilled out of the terminal in panic onto the runway apron, and if he moved the plane, he risked "ingesting" a passenger in the plane's engines.
The pilot said the plane sat on the runway for four hours before the plane was allowed to be moved on the field.
You can read the full account from the pilot -- who is not identified -- at thePilot Reports forum.
Sand Storm
Sand Storm activity results in reduced visibility and the ingestion of sand and dust particles into engines, pitot static systems, conditioning packs, causing blockage and corrosion.
Aircraft avoid any airspace that has volcanic ash in it for a simple reason: the ash can wreck the function of propeller or jet aircraft, because it is so fine that it will invade the spaces between rotating machinery and jam it – the silica melts at about 1,100C and fuses on to the turbine blades and nozzle guide vanes (another part of the turbine assembly), which in modern aircraft operate at 1,400C.
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