Aircraft tyres: Air or nitrogen?

[vee-tail-1]

When I was working at LHR in the old BOAC hangar, we inflated B 707 & 747 tyres with nitrogen. I am retired now, but a young engineer friend tells me that air is sometimes used now. I thought there was a BCARS requirement for nitrogen, and wonder if air being cheaper is now used to save money?:bored:

[sevenforeseven]

Nitrogen is used. Air can be used but in emergency use only when N2 is not available, but must be replaced with N2 first opportunity.:)

[Piper19]

Always nitrogen, never air.

[Milt]

Heartell that the oxygen in the air at high pressures reacts negatively with some of the materials forming tyres.

More info anyone?

[stevef]

That's right, Milt. There was a fatality some years ago when a tyre exploded, puncturing the fuselage and a child was sucked out (I suppose blown out is more correct). I think it was over Israel but I don't remember the aircraft or airline.

[Milt]

By the way - what limits the number of times an aircraft tyre can be retreaded other than obvious physical damage ?

And is it still SOP to give the tyres a kick during pre-flights?

[Mr.Brown]

From B737CL AMM 12-15-51
"Air can be used when nitrogen is not available if the Oxygen content in the tire will not be more than 5% by volume".

[om15]

Reference CAP747 Generic requirement no 16. ( Previously issued as AWN no 70).
".... all braked wheels of retractable landing gear units on aeroplanes defined in para 1 will be required to have tyres inflated with Nitrogen or other suitable inert gas, and maintained such as to limit the Oxygen content of the compressed gases to not greater that 5% by Volume."

key points seem to be braked wheels and retractracable gears,

regards,
om15.

[sevenforeseven]

Mr.Brown, thank you. I rest my case!!!:ugh: :D

[keep em flying]

Oxygen = fire hazard!! hence nitrogen instead of air.

[vee-tail-1]

Thanks guys, it's still N2 then:)

[419]

Another of the reasons for using nitrogen ( I was always told this was the main reason), is that a nitrogen molecule is approx 4 times the size of an oxygen molecule, and as rubber is slightly permeable, the leakage rate is far less. ( I know air is only about 22% oyxgen, but that is still enough for leakage to be a problem).

This leakage isn't really noticeable at ground level, but once you get to high altitude, it then becomes more of a factor, due to the higher differential between the internal pressure of the tyre and the ambient pressure.

[Rigga]

Another of the reasons for using nitrogen ( I was always told this was the main reason), is that a nitrogen molecule is approx 4 times the size of an oxygen molecule, and as rubber is slightly permeable, the leakage rate is far less. ( I know air is only about 22% oyxgen, but that is still enough for leakage to be a problem).
This leakage isn't really noticeable at ground level, but once you get to high altitude, it then becomes more of a factor, due to the higher differential between the internal pressure of the tyre and the ambient pressure.


This might be an observation on the use of N2 - but is certainly not a reason for it.
The "Reason" is it's inert properties.
Personally, I've had N2 sent 100's of miles to me, rather than use air in an aircraft.
I would rather use Helium!

[sevenforeseven]

Please someone call a "sensible" engineer.:ugh: :{

[bvcu]

Think you will find that USAF still uses air . FAA i think is the same as the CAA and most other authorities in specifing nitrigen . DC8 crash in saudi a few years ago i think was the final catalyst.

[Perrin]

It was a L1011 from Sauda. Wheel assy had overheated on TO

[Mr.Brown]

Personally, I've had N2 sent 100's of miles to me, rather than use air in an aircraft.
How do you tell your maintrol or whoever that you won't go by the AMM and put air in the tire( Assuming that your particular aircraft allows for air)?

[tribo]

USE DRY NITROGEN GAS (WHEN REQUIRED)
Nitrogen will not sustain combustion and will reduce degradation of the liner material, casing plies and
wheel due to oxidation.
http://www.goodyearaviation.com/tirecare.html
(Page 11)

[stevef]

Further to tribo's post:
http://www.dunlopaircrafttyres.com/tyrecare/dm1172/DM1172.pdf contains excellent information (a lot of which I'd forgotten)
and this, from Trans Technical Services Co Inc:

WHAT HAPPENS WHEN A TIRE EXPLODES? Air Safety Week
had an interesting article on the energy released by exploding tires in their August
7, 2000 issue. It was addressing the tire failure on the Concorde. If you go to page
3 (of that issue) you will find a chart − Energy Released by Catastrophic Tire
Deflations. If you “used the same numbers” for a P-3 (Navy aircraft) main
landing gear tire at 200 pounds per square inch (psi) tire pressure to approximate
the energy released by a 747 main landing gear tire failure (194 psi) − it would be
301,071 foot pounds . . . . equal to 0.60 sticks of dynamite. If the tire burst at
the maximum pressure of 1,170 psi it would release 1,215,789 foot pounds of
energy − an amount equal to 4.4 sticks of dynamite.

[Piper19]

And is it still SOP to give the tyres a kick during pre-flights?

Hehe, I've seen this so many time, pilots giving a kick to a tyre at about 200PSI. Only gives him pain at the foot and gives me a laugh. Even a deflated tyre will not move under a foot kick.

[matkat]

Think you will find that USAF still uses air . FAA i think is the same as the CAA and most other authorities in specifing nitrigen . DC8 crash in saudi a few years ago i think was the final catalyst.
The DC-8 nationair crash was nothing to do with what the tyre was inflated with it was caused by underinflation coupled with a very long taxi in hot conditions, the tyre overheated and caused it to explode on retraction resulting in a massive fire in the wheel well, further cause was the inability of the saudi controller to understand the gravity of the situation, the aircraft made it to approach but the damage was so great due to the fire when the gear was extended the aerodynamic forces caused the tail to break off resulting in the crash. I actually visited the crash site, very tragic indeed but a lesson to us all.

[Rimmer]

Hi Guys

I had the old AWN 70 so heres what it says >>>>>>>

A fatal accident involving cabin decompression and fire has highlighted another mode of
tyre failure in flight where a tyre may fail explosively without any significant prior
degradation. A tyre inflated with air and subjected to excessive heating, possibly caused
by a dragging brake, can experience a chemical reaction resulting in release of volatile
gases. Such a chemical reaction in the presence of the oxygen in the contained air may
result in a tyre explosion in a landing gear bay and/or an in-flight fire since it appears that
the protection normally afforded by conventional pressure relief devices in the wheel
would be incapable of responding adequately to the rapid increases in temperature and gas
pressure associated with auto-ignition.
2.4 Laboratory material and tyre burst testing indicates that the risk of auto-ignition can be
reduced by using an inert gas for tyre inflation and servicing.
2.5 Other potential benefits may accrue from the use of Nitrogen as it will tend to reduce
wheel corrosion, tyre fatigue and the risk of fire when fusible plugs melt due to brake
overheating.

Sure the CAA wont mind its been moved now anyway.

[Blues&twos]

I may have misunderstood something here, please tell me if I have (I'm sure someone will).

Given that there is approx 21% oxygen in atmospheric air surrounding everything, how does inflating a tyre with N2 reduce the risk of fire caused by an overheating brake?

[spannersatcx]

Nitrogen is an inert gas and as far as I know that doesn't aid combustion.

[Rimmer]

Blues&twos
Dont forget the air we are talking about is inside the tyre and at hundreds of degrees centigrade, it interacts with the tyre makeup and contributes to an explosive mix, the surrounding air is cool and safe

[Blues&twos]

Blues&twos
Dont forget the air we are talking about is inside the tyre and at hundreds of degrees centigrade, it interacts with the tyre makeup and contributes to an explosive mix, the surrounding air is cool and safe

Thanks Rimmer, that makes sense.

Spanners - I know N2 is inert, I'm not that daft! Mind you, you weren't to know that.....

[snips]

The Partial Pressure of Oxygen in a Tyre filled air is much greater. This causes the problem by making O2 a much improved oxidisation agent. They have a similar problem in dive recompression chambers.
Cheers
snips
:8

[Ladytech]

Most of the reasons are correct. We use DRY nitrogen
mainly because of the possible water contamination.
Corrosion and also on an overheated tire it will turn to steam
and react with the tire & tire pressure. Heat is the main cause
of premature tire failure.

[PaulW]

I think this young engineer has misunderstood, the terms we use over our 2way radios and what is now a colloquial term for a nitrogen bottle and regulator trolley. When asking our maintenance workers to deliver a set of "air bottles" to a stand we mean nitrogen bottles. Nitrogen and Oxygen sound very similar on a crackly often breaking up radio. No confusion when asking for a set of oxygen or a set of air bottles.

[glhcarl]

The Saudia incident had nothing to do with a tire (tyre). It was the bead on the rim that failed and holed the pressure deck over the main landing gear wheel well, the tire never lost pressure. The accident investigation revealed undersized beads on some of the L-1011 MLG wheels.

Addtionally, I was in the USAF from 1965 to 1969 and we used nitrogen to service tires at that time.

[magpienja]

This reminds me of a post I put in the spectator section some weeks back never did get the answer I was looking for maybe some of you guys could tell me, I drive a 44 ton truck it has 16 wheels inflated to 110psi, I remember when being close up to a 737 looking at the main bogies and thinking how on earth can just 4 main wheel take all the weight of a fully loaded 737 from what I gather this can be 75.000kgs, I know there a 2 wheels at the nose but I would think the mains carry most of the weight but how on earth can such a small number of wheels carry that weight without even bulging.

Nick.

[Wodrick]

Have a look at the references quoted in this thread posts 18 & 19 the definitive guides.
A/C tyres, while of similar construction to vehicle tyres, are incredibly rigid even when deflated. It needs a trained eye to spot a low pressure or deflated tyre visually, a gauge is normally required. When you throw in the typical inflation pressure of about 200psi (dependent on type) I think you find the answer.

[mmrassi]

And in Iran...I don't know about western fleet , but I was working with an Airline for a short time and they all used air to fill Tu154Ms tires . Good to know that Tu154 tires are not Tubeless.

[Mr.Brown]

mmrassi,
What was the name of that airline so I can make sure nobody I know (except for poeple I don't like) will fly with them!!!
Oxy in aircraft tires??:ugh: Tell me your Englihsh is limited please. :hmm:

[Edgar Jessop]

Magpienja, aircraft tyres run at a deflection of about 30% as opposed to automotive ones typically 10%, and are not designed to be continuously run. As they roll, the heat builds up. They do not reach an equilibrium temperature as ground tyres do. If you taxied an aircraft for long enough, its tyres would overheat and burst. The same is true for underinflated tyres, the rapid heat build-up kills them very quickly.

If you designed aircraft tyres to be capable of continuous running the weight would increase massively.

[mmrassi]

Mr.Brown and other other guys !

Really sorry for incorrect writing . I was thinking of oxygen at the time of writting and that's why i wrote oxygen instead of air . really sorry , The airline name is Caspian and is a real safe one because the only airline that never had an accident though it has high number of flights and its planes are always in flight .

again sorry....

[AEROMEDIC]

Air also introduces moisture to the wheel hub and causes corrosion. If you go to the trouble of using dry air from bottles, then why wouldn't you use nitrogen? :confused:

[chasb441]

Tyres inflated with air and subject to excessive heating due to braking action can experience a chemical reaction releasing volatile gases. In the presence of oxygen this can cause an explosion. AWN's require that tyres on aircraft over 5700kg with retractable landing gear should be inflated with a suitable inert gas with oxygen levels no greater than 5% by volume.....Such as nitrogen :ok: