How dangerous is volcanic ash on airplanes

When Taal Volcano erupted last January of this year 2020 spewing volcanic ashes into the air, Metro Manila was equally affected as ash started pouring over the region. The Ninoy Aquino International Airport (NAIA) was not spared from the ashfall, hence, flights inbound and outbound Manila were suspended. So how dangerous can volcanic ash or ash clouds be to aircraft? Was it necessary to suspend flights?

Volcanic ash are indeed very dangerous to airplanes. Engines ingesting volcanic ash lose thrust or even flame out. It may also cause false or erroneous readings as the ash may cover the aircraft sensors. Volcanic ash particles ejected into the atmosphere may also abrade the forward facing surfaces of airplanes like the windscreens, compressor blades, and fuselage surfaces.

Ash can cause aircraft engines to flame out. When ingested, the ash particles will melt as the melting temperature of the glassy silicate found in ashes is lower than the combustion temperature in jet engines. The problem is when these reaches the cooler parts of a turbine, these particles may re-solidify and form into crystals in other parts of the engine which may block air filters, clog fuel nozzles, and damage components in the engine that may cause a flame out or the total lose of power.

Air sensors are very important and ash blocking these may cause erroneous readings. This may affect a pilot's decisions in the flying the aircraft as information fed into the cockpit's screens such as altitude, heading, and speed, are wrong. 

Ash may also scratch the surfaces of the front windscreen resulting to poor visibility. Its simply like rubbing a sandpaper on an aircraft's outer windscreen. Another effect of volcanic ash may be the contamination of the ventilation and pressurization system which may set off alarms.

Ashclouds may be invisible to the human eye and you will only know that you may be flying in a volcanic ashcloud after the effects kick-in, which is actually dangerous to the flight.

In 1982, a British Airways Boeing 747 flew through ash brought by the eruption of Mount Galunggung in Indonesia. This caused all 4 engines to flame out. The pilot later on managed to restart 3 engines and managed to land the aircraft safely.

In an era where air safety is paramount, it was indeed necessary to suspend flights to prevent putting airplanes, the passengers, and crew they carry at risk.

As for the NAIA suspension of operations, it was necessary until the runway and ramp areas are cleared of volcanic ash. Add also the health hazards of ashfall to the airport ground personnel and ramp workers.

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