Pilot Revealing Myth Regarding the Aircraft Cabin (NOT SOLVED YET)


Yesterday, I was on AirAsia flight travelling from Thailand to Malaysia. I was delighted that there is an awesome magazine by Travel3sixty (make sure you check it out). It showcases lots of travel information and special promotions. Particularly, there is a section talking about interesting facts in the aircraft cabin.


Pilot’s Perspective: Myth vs. Reality by Captain Lim Khoy Hing (from Travel3sixty In-flight Magazine)

Here are some of the highlights that I personally find to be interesting. Captain Lim Khoy Hing debunks aviation myths and reveals some little-known facts about the aircraft. However, some of the statement lights up my new curiosity (I will highlight them in red in the following paragraphs). Part of the following paragraphs was taken from Travel3sixty.

Less Oxygen at Higher Altitudes. Myth or Reality?

The idea that there is less oxygen at higher altitudes is a myth. In reality, the amount of oxygen in the atmosphere (21 percent) remains almost the same regardless of the altitude. What actually happens at higher altitudes is that the reduced atmospheric pressure (partial pressure effect) makes it difficult for oxygen to be absorbed into the bloodstream. Due to this, the aircraft must be pressurised when flying at higher levels, so that your body is able to absorb about the same amount of oxygen as the plane climbs to cruising altitude.

Even though you may be cruising at 35,000ft, the aircraft cabin altitude is, in fact, automatically adjusted to simulate a lower one, such as from 6,000 to 8,500ft. This is achieved through pressurisation. The aircraft cabin is just like a balloon – air from the engine acts like a pump to pressurise the cabin in order to ensure that pressurisation is maintained.

Recirculation of Air in the Aircraft Cabin.

Due to the restricted space within the aircraft cabin, passengers might mistakenly think that the recirculation of air by the air-conditioning system can cause the spread of viruses. The truth is, cabin air is probably cleaner than the air in a regular office building! Fresh air is drawn from the outside and filtered through hospital-grade filters, which remove 99.97 percent of bacteria and tiny particles before it is channelled into the cabin. The plane’s cabin air is refreshed about 15 to 20 times every hour.

Occasionally Odour from the Air Conditioner.

On rare occasions, passengers in smaller jets might notice an odour, similar to that of a car’s exhaust gas, shortly after pushback from the terminal gate. This is due to the plane’s exhaust gas being drawn into the air-conditioning system. The culprit is usually strong headwinds, causing the air to flow back through the air-conditioning pack inlets, but the good news is that such unpleasant odours quickly disappear.

So, is this something that we shouldn’t be inhaling? I am wondering how safe is this exhaust gas to us.

Low Humidity in the Aircraft Cabin. So, drink more water.

And speaking of cabin atmosphere, it’s a fact that cabin air is very dry – containing only about 12 percent humidity, it is drier than most deserts! Dehydration can make you feel more tired and prone to headaches, and cause increased discomfort when wearing contact lenses. To prevent dehydration, passengers are advised to drink plenty of water, especially on long-haul flights, and to avoid consuming caffeinated beverages, as these have a diuretic effect.

Is this normally what the stewardess was serving us? Tea or coffee, sir?

Blue from the Sky, Not Poops.

You might have heard stories about ‘blue ice’ or ‘poopsicles’ dropping from the sky, giving the impression that human waste was being indiscriminately dumped from passing planes.

There may have been such occurrences during WWII when fighter or bomber planes did not have the high-tech flushable toilets that we have in modern aircraft today. In fact, the flight crew would urinate in bottles and dispose of their waste in cardboard boxes! Thankfully, this is no longer the case today.

Incidents of ‘blue ice’, which, in fact, is blue coloured deodorising liquid, only arose with later aircraft. The liquid is purely a cleansing and treatment agent for the waste system and does not contain any waste mixed in it. Sometimes, these fluids can leak from the plane in mid-flight, and instantly freeze at the bottom of the aircraft. As the fluid continues to leak, more and more ice forms until at one point, it detaches from the plane and drops to the ground – as ‘blue ice’. But rest assured, it does not contain any human waste.

Is the blue coloured deodorising liquid something safe? Why should we let them leak from the plane?

Toilet Waste has never been disposed from commercial planes in mid-flight.

Today, modern airborne waste control technology in your Airbus A320 or A330 is highly efficient. It relies on strong suction to eradicate waste with just a fraction of a gallon of water. The waste is then accumulated in special tanks in the plane and is sanitised and deodorised. After the aircraft lands, the waste is taken to a treatment facility for processed disposal. Passengers can rest easy in the knowledge that toilet waste has never been disposed from commercial planes in mid-flight; only water from the sinks is dumped directly through the drain mast into the atmosphere.

Has the sink “water” been treated before dumping into the atmosphere? How if I spit into the sink? Anyway, is this legal?

About the Author

captain-limCaptain Lim Khoy Hing is a former AirAsia Airbus A320 and AirAsia X A330/A340 pilot who also used to fly the Boeing 777. He has logged a total of more than 25,500 flying hours and is now a Flight Simulator Instructor with AirAsia X.  In his spare time, he shares his opinion on aviation issues with others. For more air travel and aviation stories, check out his website, ‘Just About Flying’ at askcaptainlim.com


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