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?

[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]

Tyre inflation.

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!!!

[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]

Originally Posted by 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.

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.

[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]

Perrin

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

[Mr.Brown]

Originally Posted by Rigga

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]

From GoodYear AIRCRAFT TIRE CARE AND MAINTENANCE manual

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/t...172/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]

Originally Posted by Milt

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.