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Volcanic Ash

Volcanic Ash

After the recent spate of airlines cancelling flights between various cities due to the volcanic ash from Chile, most passengers were thankful for the ‘safety first’ attitude of the airlines.

Some were, however, confused when it became apparent that international flights into and out of the ‘closed’ airports were still operating. More on this later, but first, exactly what were the airlines concerned about, and could it have affected smaller operators such as student pilots around the country?

Firstly, the important aspect about volcanic ash to remember is that not only is it very abrasive material, it also has a low melting point and is virtually impossible to avoid if you do not know it is there. Especially at night or in IMC, you can’t see it and since it does not contain any moisture, current generation aircraft radars can’t detect it. This is why the much discussed 747 total engine failure occurred many years ago over Indonesia – it was night and the crew did not know it was there – they flew into it. Luckily the monitoring and reporting of potential volcanic ash areas is now vastly improved – and hence the incidences of ash encounters have markedly decreased. So what does the ash do, and why?

Volcanic ash is not like the ash that floats serenely into the sky above your campfire. It is in fact extremely small (less than 2 mm down to 1 micron) sharp edged bits of rock and glass. Think of it as essentially coarse grit airborne sandpaper that if exposed to heat will melt and fuse onto the nearest hard surface – in the case of an aeroplane – the turbine section. So, the act of flying through the ash results in abrasion of windscreens, pitot tubes and surfaces resulting in an inability to see and associated performance degradation. The ash, if brought into the cabin via air-conditioning can be toxic, possibly requiring the use of oxygen for crew and passengers, and as it is very small, will end up everywhere, including inside electrical equipment.

Engines, especially turbines, do not like ash ingestion. Apart from the abrasion of compressor blade edges reducing compressor performance, glass particles may melt in the combustion chamber if a high thrust rating is used, and the melted material will cool and solidify in the turbine, disturbing the flow of high-pressure combustion gases. In the worst case, the engine may stall. Interestingly, in all reported ash encounters, the crew of the aircraft affected have been able to restart at least some of the ash-stalled engines. The lesson from this is even if all engines are stalled, get out of the ash, get to best relight speed, and continue the restart procedure until the engines restart.

The increasing ability to forecast volcanoes and their ash clouds has resulted in a reduction of ash encounters over the past 20 years. To avoid a known ash cloud requires knowledge of the event through the volcanic ash advisory centre (VAAC) in your area – Darwin in our case. Notams are issued, and maps of the affected areas are published. Expected heights of the ash are promulgated – the Chilean volcano was reported between in areas above FL150 and also areas above FL200. The majority of the ash was in the high level jet stream circling the globe. This knowledge enabled pilots to avoid the areas and safely fly, albeit at a lower than usual level or with a longer track. Essentially, don’t fly in an ash area.

If however, you do encounter unreported volcanic ash, how will you know? The presence of the following, amongst others, may help you recognise an ash encounter: acrid odour not unlike electrical smoke, rapid development of engine problems, orange glow in engine inlets, dust and smell in cockpit, low visibility and st.elmo’s fire. Engines operating at high thrust settings are more prone to ash deposits in the turbines, as the engine running temperature may be higher than the ash melting point.

So what do you do? Turn around 180º and decrease thrust (to decrease engine temp) at the first sign of volcanic ash. Oxygen masks on (to continue breathing), increase bleed air demand through engine and wing anti-ice (increases the fuel/air ratio to decrease possibility of engine surge and flameout) and start the APU. Seems easy, right? Well, have a think about the effect of an all engine flame-out with no APU at night – prevention is vastly better than the cure. A good knowledge of the normal procedures for your particular aircraft is, as always, essential.

But what about small aircraft? The effects are the same – ash abrasion and ingestion will damage aircraft windows and surfaces. The engine, whilst not a turbine engine, may still suffer the effects of ash deposits reducing cooling and possibly clogging carburettors etc. The advantage of a small aeroplane is that you are flying at a lower altitude – and with events such as the recent Chilean volcano low altitudes over the affected areas were perfectly safe. Obviously, with volcanos such as Soputan in Indonesia shutting down the nearby airport of Manado, had you contemplated flying a light aircraft near there it would have been a different story – dense ash clouds depositing thick layers of ash not unlike snow everywhere.

The key to volcanic ash is avoidance and common sense when operating an aircraft in an area where volcanic ash has been forecast or observed. Avoid the reported levels and fly around the reported areas. International carriers continued to operate into airports such as Adelaide and Melbourne by flying below the reported ash levels – a completely legitimate and safe course of action backed up by appropriate risk management. The Chilean volcanic ash was at high level and very dispersed – flying at FL180 or even lower was a small price to pay to ensure passengers were deposited at their destinations. Unlike Europe, the Australian regulators did not shut down the airspace: airlines were left to their own risk management devices when deciding whether or not to operate.

As a private pilot, reading this may seem a bit over the top – when is this ever going to happen to me? Well, I did not think I would ever see volcanic ash grounding nearly the entire Australian domestic aircraft fleet either, and flying on one of the clearest blue Australian days I have seen lately with only international callsigns to accompany us was a different experience. As always, read further on what I have written about and broaden your knowledge base. You never know when one day (or night) you may need it. Safe flying.

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