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Changing the Oxygen Bottle in P2-SDP

Story and photos by Mandy Glass

Martin Dabrani, who joined MAF in 2021 as a licensed avionics engineer, had recently been assigned to replace the 10-liter oxygen cylinder, mounted in the tail of our Cessna 208 Caravans P2-SDP aircraft.

“Every five years, the oxygen crew bottle, as they call it, is due for a hydrostatic test. We don't do that sort of testing in the country. So, when it's called up after five years, we remove it, send it away overseas, and we put a new one in. We always have a spare in stock. It's a scheduled maintenance task that the maintenance controller keeps track of.

For the aircraft, oxygen bottles are usually green. Some aircraft have portable ones that are mounted next to the pilot’s seat, but this big one is in the aircraft's tail section with outlets at the front for the pilots to connect their masks to,” Martin explains.

If our pilots are flying above 10,000ft for over 30 minutes, they are required to wear their oxygen masks. Above 10,000ft, the oxygen saturation in the blood decreases rapidly affecting the concentration of the pilots. In an emergency, every second counts for swift decision-making. Therefore, CASA PNG has restricted passenger flights above 10,000ft to 30 minutes. Flying in the highlands of PNG requires occasional climbing to higher altitudes because of mountains or cloud build-ups. Without the oxygen supply, the pilots would need to descend below 10,000ft every 30 minutes, which can be difficult if weather or mountains do not allow such a descent.

Even though our aircraft would cater enough oxygen for our passengers, the nature of our operation does not require oxygen masks for passengers. To fly higher than 10,000ft for over 30 minutes only makes passengers a bit sleepy. Martin continues to explain the challenging exercise to get the oxygen bottle in and out the aircraft. “It’s a bit tricky, a kind of a difficult job due to its location and the weight of the bottle. You have to hold it up and then secure it. I could get someone else to help, but it would be awkward to squeeze two guys into the small tail section of the plane. Probably two skinny guys will do…”

Andrew Campbell, MAF PNG’s Maintenance Controller, points out a safety risk, the engineers need to be aware of: “The tools used to work on the oxygen bottle and its replacement aren’t allowed any grease or oil on them. Serious aviation accidents have occurred due to oxygen being a primary component of combustion. If a source of ignition (ie spark from a switch) is available, then things burn very nicely with oxygen. Therefore, great care is required by our engineers to keep tools clean and free of grease due to fire risk.”

It took Martin about 5 hours to complete the task.

“It’s quite a big job. We can’t go any faster and we have to complete paper work too. It also took time to top up the oxygen in the new bottle to its full capacity. The full bottle will weigh about ten kilos. So, it’s easier to put the bottle in when it’s not quite full, secure it, and then top it up. Also, the filling pot is on the aircraft structure, that's why we couldn’t fill it outside.

We also have to do a leak check to make sure there are no leaks at the back. For this we hook up the mask, do some breathing ourselves, and make sure the oxygen flows properly.” Over the course of this year, three more of our aircraft need the oxygen bottle changed. Martin is one of 13 engineers servicing our aircraft at our Mt Hagen based maintenance facility, helping to keep our fleet operational so we can serve the communities in the rural area to bring help, hope and healing.

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