Out of the Ashes

The finest cut

Weeks, or even months, before molten rock bursts through the earth’s surface, small tell-tale jets of steam can signal the approaching eruption. When the explosive event occurs, it has the potential to blast the volcanic material high enough into the atmosphere to create a hazard for airliners cruising as high as 45,000ft within minutes of the eruption. The column’s vertical path ultimately slows and begins to spread as gravity and atmospheric temperature changes take effect, but the hazards have only just Begun.

The ejected volcanic ash is very fine and is easily carried upon the wind and, in the upper atmosphere, by the jetstreams. Consequently, the region affected by the eruption can reach far beyond its immediate area as was seen in 2011, when the ash from Chile’s Puyehue-Cordon Caulle volcano circled the globe and impacted upon flights operating in Australia. Furthermore, it can take years for an ash cloud to totally vanish.

Even though the particles within this ash are very fine, less than two millimetres in diameter, it can have a significant effect on aircraft. From engines and windscreens to airconditioning and avionics, very few components are immune and each year airliners are written off by the damage they suffer at the hands of volcanic ash.

‘On the flightdeck the same light show can be seen.’

The silent enemy

It seems at odds with logic that mammoth high-tech machines such as airliners can be held to ransom by elements that can be measured in microns. However, it is partly that very issue of size that allows the volcanic ash to infiltrate an airliner so Effectively.

When wood is reduced to ash, the by-product is soft, but this is not the case with volcanic ash. Volcanic ash is comprised of small rock fragments, sulphuric acid droplets, minerals, and silica. This form of ash is abrasive in nature and not broken down by water – it absorbs it. With an airliner’s jet engine core reaching temperatures of 1,400 degrees Celsius, the silica melts, forming glass and bonding with the blades and vanes within the engine. This disrupts the airflow through the engine, which in the first instance may result in surging, but can ultimately result in the engine, or engines, flaming out.

In turn, the hydraulic, electrical and pneumatic systems can fail, leading to the aircraft relying on very finite battery power and with the pressurisation system failing, among many other complications. The abrasive nature of the ash can erode the entire airframe, but the immediate threat is posed by the damage to the windscreen, limiting the pilots’ forward visibility on the approach and Landing.

As the volcanic ash absorbs water, it has the potential to create short circuits across the electrical system and avionics, while the cabin air may become heavily contaminated, requiring flightcrew to don their oxygen masks.

For an aircraft inadvertently entering the ash cloud, a number of accompanying symptoms can occur. The smell of sulphur, or an electrical burning smell can pervade the aircraft and a haze can fill the cabin and flightdeck with dust settling on all surfaces. The fluctuating pressurisation system can be felt in the passengers’ ears if subtle, or worse if the system fails altogether. From their windows they may see torching, flashing from the rear of the engines, or the electrical tentacles of St Elmo’s Fire creating an eerie glow on the airframe and the engine inlets.

On the flightdeck the same light show can be seen, while the static discharges interfere with the radios and communications. The airspeed can begin to fluctuate rapidly and erroneously, triggering spurious warnings, as the outside sensors begin to clog with ash. The engines begin to surge and protest, choked of airflow until the point of strangulation before flaming out into silence. With the engines failed, the electrical generators are also compromised and on board the cabin lights go dim as the airliner is forced into a descent by a lack of thrust and the forces of gravity.

This is the situation Speedbird 9 found itself in that night to the south-east of Jakarta, when all four engines failed. Thirty-five years ago, the crew did not have the benefit of the awareness or education in the ways of volcanic ash that we have today. Furthermore, the encounter occurred at night when there was not the ability to see the ash cloud looming ahead while the weather radar is only suitable to detect exactly that – weather. Airborne radar systems can detect moisture, but not the components of volcanic ash.

The fact that the crew were able to restart their engines and safely land at Halim Airport is a testament to their ability in a dire situation. Fortunately, much has changed in the intervening years and airlines and pilots alike are far more educated in the ways of volcanic ash.

A global awareness

According to the United States Geological Survey, there are about 1,500 potentially active volcanoes worldwide, of which about 500 have recorded eruptions. Some volcanoes are tracked by Volcanic Observatories which take seismic readings, measure deformations, and monitor gases among other warning signs. However, around the world more than half of the volcanoes are not monitored.

The International Civil Aviation Organization (ICAO) has established International Airways Volcano Watch (IAVW) to provide warnings to the aviation community, comprising of nine Volcanic Ash Advisory Centres around the world. These units advise the international aviation industry of the location and movement of clouds of volcanic ash.

In Australia, the Volcanic Ash Advisory Centre in Darwin covers Indonesia, Papua New Guinea and a section of the Philippines. The volcanoes are colour-coded by an internationally recognised four level system ranging from a ‘Green’ normal, non-eruptive state, through to ‘Red’ which forecasts an imminent eruption with ash reaching the upper Atmosphere.

All arms of the aviation community play significant roles in gathering and disseminating information, including air traffic management and the Bureau of Meteorology, which provides Volcanic Ash SIGMETS as part of their aviation weather and warning services. Additionally, many airlines possess their own system of notification of volcanic activity to flightcrews which can be relayed through the company ACARS system.

Also within the airlines are dedicated teams that assess, mitigate and monitor the risk associated with volcanic events. Just as the volcanoes have levels of threat, the teams have a range of plans of action based upon the circumstances at the time. It may call for rerouting flights well clear and upwind of any potential danger, or cancelling services altogether.

These teams constantly monitor the situation and could be seen in action during the recent events in Bali. On a daily basis flights were cancelled when the risk was assessed as too great, while an unexpected change in wind direction did see a potential window for operations during that period. For this to occur, the airline teams need to be both strategic and dynamic in order to react when the opportunity avails itself. This may also involve positioning crews at the ready in relatively nearby ports.

At all levels and across the globe, government bodies and airlines alike constantly monitor the potential for volcanic activity with the information available. The view is to mitigate against an ash encounter ever occurring as even a minor encounter can cause substantial damage to an aircraft. Even so, there are procedures and training in place for pilots should they be faced with volcanic ash despite all the measures designed to avoid it.

The pilots’ role

Each make and model of airliner will have its own defined set of procedures to deal with flight into volcanic ash, just as each airline will have its own training syllabus, so it is impossible to cover every case here. As such, each relevant set of operating manuals and procedures should be consulted. The overwhelming message is one of avoidance, but the nature of aviation is to prepare flightcrews for all manner of emergency scenarios and a volcanic ash encounter is one such potential Emergency.

‘Airline teams need to be both strategic and dynamic.’

Should the encounter occur, first and foremost the crew needs to continue to fly the aircraft safely and avoid the numerous distractions that will undoubtedly occur, from crackling radios and flickering lights to St Elmo’s Fire. As the pitot probes may be feeding erroneous data, it is important to fly an appropriate pitch attitude, and power setting if able. The indicated airspeed shoud be treated with a degree of suspicion and there may be a need to initiate the non-normal procedure for flight with unreliable airspeed at some point.

Just as visual flight rules pilots are trained for an encounter with cloud, initiating a 180-degree turn may Climbing above it may not be possible and even if it was, the increase in thrust would actually increase the engine temperature and in turn, increase the melting debris bonding to the engine, making the situation Worse.

For this reason, a reduction in thrust to idle may lessen the buildup of molten material, although it will also make the 180-degree turn a descending turn, so terrain must be considered. In autothrottle-equipped aircraft, it may be worth considering disconnecting the autothrottle to avoid the thrust increasing unnoticed. Notably, with the engines at idle, as opposed to flamed out, electrical power, bleed air, hydraulics and pressurisation all remain available. If possible, starting the auxiliary power Unit (APU) may be able to provide an alternate source of electrical power and/or bleed air for engine starting on certain aircraft types.

On the flightdeck the crew should don their oxygen masks and goggles to counter the fumes and haze. Turning on engine and wing anti-ice devices and all air-conditioning packs may also increase the engines’ stall margins by increasing airflow, while selection of continuous ignition will be of benefit if a restart is needed.

Should the unthinkable occur and multiple engines flame out, cycling the fuel switches/start levers to ‘off’ and then ‘on’ in an attempt to restart the engines is a procedure common to many aircraft types. The engines may be very slow to spool up, so they need to be monitored closely and patiently and guarded against rapidly rising exhaust gas temperatures (EGT).

This would be a very bad day for any airline crew, but it is of some reassurance that pilots are trained in the specific procedures relating to their specific aircraft in this situation. And like all emergencies, it is always best to be thoroughly prepared.

Ash clouds rising

While aircraft are still vulnerable to volcanic ash and without a system of onboard detection, pilots and passengers are in a totally different situation to when Speedbird 9 had its ash cloud encounter more than thirty years ago. International bodies, airlines and pilots are far better informed, educated and trained in this threatening phenomenon. A wealth of information is continually gathered and shared around the world and airlines and pilots alike opt for the conservative option.

This approach may lead to cancelled flights and the disruption of family plans, but the extensive queues in airline terminals are truly a small price to pay. The commercial impact upon airlines is also great, but their crew and passengers’ welfare must always be the overriding consideration. In aviation, safety must always be the priority and there is nothing to be gained by challenging Mother Nature when the ash clouds are rising.