View Full Version : Decend for Ozone??

16th Jul 2006, 07:33

I Overheard a couple of United flights overflying nothern Canada today that asked to descend because of Ozone. Would anyone be able to explain why they do this??


16th Jul 2006, 09:29
Ozone is not very good for the cabin inhabitants health.

Most commercial flights cruise near the edge of the troposphere where naturally occuring ozone rarely exists in quantity. Ozone can enter and recirculate in even modern cabin air filtration systems including the HEPA types used on the 777. In an event such as you describe, a lower altitude is the only remedy.

A Concorde flight would not have requested a descent as it is (as far as I know) the only airliner to include an ozone-removing component in the air system.

16th Jul 2006, 09:41
How do they know about the ozone, do they have ozone sensors?

16th Jul 2006, 13:51
I thought ozone was the layer around the earth protecting us from the sun's radiation- like when they say a hole in the ozone layer has gone is dangerous, i didn't realize ozone is a bad chemical entering the aircraft.

Spanner Turner
16th Jul 2006, 17:00
I know that the 747SP was fitted with catalytic converters to remove ozone from the air. The SP was certified to fly at a higher altitude than the standard classic (43,000ft I think) and as it could cruise at these altitudes for long periods of time (upwards of 9-12 hours on a trans Pacific leg) the build up of ozone in the cabin could become a problem. They were a simple device about 18-20 inches long located in the duct to each air-con pack and were just a fine honeycomb of stainless steel. These converters are just like the ones in your car (though these are made of platinum or palladium as they are designed to convert the different gases produced by the internal combustion engine) The ozone used to react with the stainless and be converted into some other less toxic gas-just plain oxygen I think. After all ozone is just a different isotope of oxygen. Chem symbol O3 as opposed to O2. It is naturally occurring but not prevalent at the altitudes that most airliners cruise at. I well remember replacing these regularly during HeavyMaintenance visits as they were bloody heavy-but from the outside just looked like a lightweight 18inch section of normal ducting.
When the 747-400 came along with itís certified ceiling of 45,000 ft, I know my companies aircraft had Catís fitted to them although I believe they are no longer fitted and/or may be an option. Not sure 100% of the reason but I guess itís because in the real world these jets rarely get above 40,000 feet and if they do it is usually only towards the end of cruise when most of the fuel/weight has been burned off and the extra fuel burn to climb to the more fuel efficient altitude is worth it. I guess the SP was the only aircraft with enough power in reserve to climb to the higher altitudes early in the flight and stay there with the ensuing problem of ozone build up over time. Theyíre removal may also be for weight saving as like I said these things were damn heavy. I know too that the 767 maint manual mentions catalytic converters but to my knowledge they have never been fitted to my companies aircraft.
Another interesting thing I remember was fitting heavy duty insulation blankets to the ceiling in the upper deck of our Jumbos. This was around 13-14 years ago and was to absorb the cosmic rays prevalent at high altitudes. My company is a long haul airline and the cabin and flight crew were exposed for long durations to cosmic radiation due to the lack of protection from the atmosphere at the higher altitudes. The egg shell aluminium skin did basically nothing to stop these extremely high frequency waves. The atmosphereís lack of protection (like the prevalence of ozone) becomes apparent at around the 41-42,000ft mark. I remember these blankets being very heavy Ė not unlike the ones that the nurse puts over you in the hospital when youíre having an X-Ray to protect your privates. Once again Iím not sure if the heavy duty blankets are still fitted or what the outcome of the trial was-or even how it was monitored. I remember it being something to do with an occupational health and safety issue for the crew. I no longer work in HeavyMaint and donít make it a habit of looking behind ceiling panels if I can help it.

Dan Winterland
16th Jul 2006, 17:11
"When the 747-400 came along with it’s certified ceiling of 45,000 ft, I know my companies aircraft had Cat’s fitted to them although I believe they are no longer fitted and/or may be an option. Not sure 100% of the reason."

Perhaps it's because there's not much ozone left these days? :sad:

West Coast
18th Jul 2006, 05:59
"How do they know about the ozone, do they have ozone sensors?"

Often times ozone restrictions are listed on the release/paperwork, at least at my previous job.

20th Jul 2006, 14:45
Your nose itches, Really.