Do you use nitrogen?

[A Squared]

A Squared,

You CANNOT take atomic nitrogen and break it down into molecules.

OK, then, I see we're really into the basics here. You don't break atoms down into molecules, you break atoms down into electrons, protons, neutrons, quarks gluons....etc. These are calleed subatomic particles.

Molecules are built out of multiple atoms, liuke when you bond two nitrogen molecules together to make a .....molecule.

Here's a link that explains the difference between an atom of nitrogen and a molecule of nitrogen. Notice that the question is asked by a 12 year old boy

I stand corrected that nitrogen occurs nearly exclusively in the diatomic form, and that is in fact what is used in aircraft struts and tires.

Yeah, and the diatomic form is a molecule. What else would it be? It's not an atom.

 

[CFIintraining]

Regulations to the use of Nitrogen

Nitrogen is required use in the tires of many if not all turbine aircraft. So putting the question of Nitrogen vs. Compressed air aside, I would like some info on some of the regulations governing its use.
I recently was at an FBO and was asking if they had Nitrogen to fill one of the main landing gear tires. I found out that they did have nitrogen but where not willing to fill the tire stating that this procedure requires an A&P.
First off is it true that this requires an A&P?
If No can anyone or at least the owner/operator do this?

If this procedure requires an A&P the regs are whacked. I would rather a incompetant person filling my tire with Nitogen than filling the O2 system on the aircraft.

Thanks

 

[ackattacker]

Nitrogen is required use in the tires of many if not all turbine aircraft. So putting the question of Nitrogen vs. Compressed air aside, I would like some info on some of the regulations governing its use.
I recently was at an FBO and was asking if they had Nitrogen to fill one of the main landing gear tires. I found out that they did have nitrogen but where not willing to fill the tire stating that this procedure requires an A&P.
First off is it true that this requires an A&P?
If No can anyone or at least the owner/operator do this?

If this procedure requires an A&P the regs are whacked. I would rather a incompetant person filling my tire with Nitogen than filling the O2 system on the aircraft.

Thanks

In theory, filling tires with nitrogen does not require an A&P since it falls under preventative maintenance. However if the aircraft is Part 135, Part 129 or Part 121 (which many turbine aircraft are) then an A&P is required. In practice, most FBO's have the nitrogen equipment under the control of A&P's and they won't want you touching their stuff.

If the tires require nitrogen it will be in the stated in the AFM. I don't think you'll find it in the regs...

This whole arguement about nitrogen vs. oxygen has gotten really stupid. Ultimately, as several people have stated, it really comes down to moisture. You really don't want ice or steam in your tires when you are dealing with high-flying high-brake energy turbine aircraft. As water approaches 100C the pressure rise is dramatic. "Shop Air" is not as dry as bottled Nitrogen, even with a water trap. I will add a few things to the "scientific discussion", however:

Many people are trying to prove "thermal stability" using the Ideal Gas Law. The Ideal Gas Law is not reality... it is only for Ideal Gass, which doesn't exist. Real Gasses have deviations from Ideal behavior due to van der Waals forces. Oxygen has more deviation from Ideal behavior than Nitrogen. For more information read the following link:

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/waal.html#c1

However, the difference is small enough that it really doesn't matter much. It does matter more in high-pressure tires than in low pressure, however.

When you are talking about Freon or similar compounds then you are in a whole different realm. Freon (much like Butane or Propane) is near it's condensation point at room temperature and hence easily undergoes a phase change (liquid to gas and vice versa) with changes in temperature or pressure. None of the "gas laws" apply. The pressure change when you boil a liquid is dramatic for only a minute temperature change. The energy associated with this transition is large, however, which is why Freon is used to transport heat energy in a refrigeration system.

 

[Almerick07]

you are all wrong, everyone knows they fill tires and struts with beer.....A BUNCH OF FREAKING IDIOTS!!!

 

[NuGuy]

Heyas All,

For those that care, rate of effusion is based on molecular weight. At any given temperature, molecules of different gases have the SAME kinetic energy, which is represented by 1/2MV^2.

However, as each gas has differing molecular weight (N2 is 28 g/mol, while O2 is 32 g/mol), the velocity of each gas molecule will be different as at a constant temperature Ma(V^2)a = Mb(V^2)b. Rearrangement yields Vb/Va = (Ma/Mb)^1/2. Thus the larger the molar mass of your gas, the slower the effusion.

Anyway, the important thing to remember is that air is a mixture, not a compound, and that the aggregate rate of effusion of air will be slower than just N2.

As for the corrosion issue...puhleeze...how many cars have you seen that had the wheels fall off due to corrosion? Steel wheels are so overbuilt its ridiculous and alloy wheels are corrosion resistant by design, so putting N2 in auto tires is as pointless as arguing on FI.

Nu

 

[retired guy]

Hey edmulroy...I`ll bet you sorry you asked.....

 

[Gryphon]

you are all wrong, everyone knows they fill tires and struts with beer.....A BUNCH OF FREAKING IDIOTS!!!

Nah, can't be.... who would want to waste thier beer that way?

 

[Wankel7]

. Do some aircraft tires really require 270 PSI? Well even if they do, there are air compressor systems that can easily handle it. Not every air compressor is like the one out in your garage.

Yeah, but would you want to roll it out the airliner sitting at the gate that needs air? I would think rolling out a nitrogen tank is easier.

Wankel

 

[avbug]

In theory, filling tires with nitrogen does not require an A&P since it falls under preventative maintenance. However if the aircraft is Part 135, Part 129 or Part 121 (which many turbine aircraft are) then an A&P is required. In practice, most FBO's have the nitrogen equipment under the control of A&P's and they won't want you touching their stuff.

Ah, no.

Applying compressed gas to a wheel assembly isn't preventative maintenance, it's servicing, and it may or may not require a mechanic. the presence of an AD may require a mechanic, as may the nature of the operation required to service the tire. Servicing the wheel assembly is more than merely inflating to a given pressure; a good inspection should be made of the tire and wheel and brake assembly any time that the pressure is checked or adjusted. Making even minor changes in pressure, up or down, has on occasion resulted in wheel explosions which have maimed or killed mechanics and line servicemen. It's not something to be taken lightly.

While 14 CFR 43 Appendix A cites removal, installation, and repair of landing gear tires as preventative maintenance (assuming no complex assembly operations are required), servicing of the tire is not listed. Further, the required tools, proceedures, materials, and publications (current and in-date) must be used, and the work must be done to publication specifications and industry standards.

Upon filling,the valve stem should be checked for leakage. Bolts, boltheads, nuts, cotter keys, fasteners, weights, etc, should all be checked for security and condition. The wheel assy should be visually inspected for signs of cracks, stress risers, etc. The bead area must be inspected for impact damage, nicks, thermal damage, etc. Thermal or blow plugs should be inspected. Brakes should be inspected for thermal damage, leakage, etc. If inflation charts apply due to ambient or wheel temperature, then these must be taken into account and applied both when checking the temperature, and when altering it by applying nitrogen or releasing it.

Most nitrogen bottles are filled to 2,000 or 3,000 psi. Improper use of regulated compressed gas can result in rapid overfilling, temperature changes that affect the inflating pressure (false readings), safety burst or explosion issues. Small wonder that many facilities don't want someone other than their own personnel using their nitrogen. Of course, use of oxygen in place of nitrogen, by mistake, can result in a deadly explosion at the time of filling, or in operation of the wheel assy.

It's more than just shooting in a little air. In some cases a mechanic may be required, in most cases, a mechanic should be used.

Ultimately, as several people have stated, it really comes down to moisture.

No, it comes down to manufacturer requirements and flamability issues. When a tire overheats (and considerable heat is generated from a normal landing, let alone an overheat condition from braking, stopping, taxiing, or operating under pressure), hydrocarbon gasses are released into the tire assy; this can become explosive. Mixing with high pressure air in a tire can result in ignition or explosion. Nitrogen is inert, and does not support combustion.

In 1987, AD 87-08-09 was issued by the FAA, for MD, Lockheed, Airbus, Boeing and BAE aircraft. It specifically calls for nitrogen or other inert gas having less than 5% oxygen, due to the possibility of a chemical reaction between tire gasses and oxygen.

Where an AD applies, a mechanic may or may not be required to perform the service and the attendant signoff; the AD will specify what can or cannot be done.

AC 20-97A discusses the fact that air diffused into a tire carcass lead to reduced tire life due to inner degradation and ply delamination.

Tire temp changes can be significant merely from taxiing, but numerous factors affect internal pressures and temps. A pressure drop means an underinflated tire, which will heat more rapidly than a properly inflated tire. More heat means reduced tire life, and an increase in the gassing process internally. Tire gassing is highly flammable. A 5 degree OAT temp change leads to approximately a 1% internal tire pressure change. The tire naturally diffuses, which occurs at a slower rate with nitrogen. Standard daily diffusion occurs at the rate of .02% in a 24 hour period, and specific allowable rates are specified in maintenance publications. The tire has vent holes which are part of the manufacturing process to release trapped moisture and gasses, which also lead to loss of pressure. Normal operation builds considerable heat.

Temps as low as 220 degrees F can significantly shorten the tire life. The bead area of an underinflated tire can become 50% hotter than a properly inflated one for any given operation, with respect to weight increases. Given that diffusion rate is greater for air or shop air than nitrogen, and that shop air supports combustion whereas nitrogen does not, little wonder that virtually all tire and aircraft manufacturers recommend or require the use of nitrogen in their products.

 

[avbug]

Ultimately, as several people have stated, it really comes down to moisture. You really don't want ice or steam in your tires when you are dealing with high-flying high-brake energy turbine aircraft. As water approaches 100C the pressure rise is dramatic. "Shop Air" is not as dry as bottled Nitrogen, even with a water trap.

Steam isn't an issue, though corrosion is. Particularly with magnesium wheel assemblies. Wheel assemblies are expensive; reduced moisture and condensation in the tire assembly means reduced corrosion inside the wheel.

Do some aircraft tires really require 270 PSI? Well even if they do, there are air compressor systems that can easily handle it. Not every air compressor is like the one out in your garage.

Where nitrogen is used, bottle pressure will always be considerably higher than the tire demands, or the bottle must be set aside for refilling.

High pressure shop air isn't supplied by a compressor, but by a strut pump...which can also be used to boost low bottle pressure with nitrogen and oxygen (but should not be interchanged in use).

As for the corrosion issue...puhleeze...how many cars have you seen that had the wheels fall off due to corrosion? Steel wheels are so overbuilt its ridiculous and alloy wheels are corrosion resistant by design, so putting N2 in auto tires is as pointless as arguing on FI.

This statement is one example of why trained personnel should be servicing wheel assemblies. Corrosion is a major issue. It's one of the main reasons for rejecting wheel assemblies in automotive applications (alloys are more susceptible to corrosion, not less, in most cases), and steel corrosion is very common. In aircraft applications, most all wheel assemblies are alloy, often aluminum and or magnesium, and these are always highly susceptible to corrosion.

Wheels falling off due to corrosion? How aboutleaking down due to leakage around the valve stem or around the tire bead due to corrosion...leading to under pressure and a blowout or explosion? Not uncommon at all.

If this procedure requires an A&P the regs are whacked. I would rather a incompetant person filling my tire with Nitogen than filling the O2 system on the aircraft.

You choose incompetence for servicing your aircraft? You want to choose between an incompetent person filling a wheel assy with nitrogen, vs. an incompetent person filling your oxygen system? What kind of a stupid statement is that? You want a well trained person doing either operation; either one involves dangerous compressed gasses that can kill, which can result in an explosion and injury or death, and both operations can hurt you after the fact if done improperly.

A competent, trained person should be doing either operation, period. And is required to be so, by the regulation. Even preventative maintenance must be done using all the tools, equipment and proceedures required by the maintenance publications and must be done to industry standard. If the work doesn't require a mechanic, it always requires the work to be done to the same standard as a mechanic would do, and the person performing the work will be held to that same standard. It must be done while referencing a current maintenance publication for that operation by the manufacturers involved. Most importantly, unlike the post above, it must not be done in ignorance.

If the tires require nitrogen it will be in the stated in the AFM. I don't think you'll find it in the regs...

Bear in mind that while referencing the maintenance publications, often more than one is required. The aircraft manufacturer may have specific direction on the operation to be performed. However, so may the wheel manufacturer, and certainly the tire manufacturer...and the user must have access to and reference each publication in performing the work.

This applies regardless of w(h)eather the operation is conducted under Part 91 only, or under air carrier regulations such as parts 121 or 135.

However, now that you mention it, any requirments specifed in any of the approved documentation is not only necessary to the continued airworthiness of the aircraft (don't follow them, then the airworthiness certificate is invalidated...see line 6 of your airworthiness certificate and the explaination thereof), but also regulatory. 14 CFR 43.13 provides the performance requirements that make this so...is is VERY regulatory...every jot and tittle of that maintenance pub, flight manual, pilot handbook or any other approved data (including AD's) applicable to your operation:

§ 43.13 Performance rules (general).

(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in § 43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.
(b) Each person maintaining or altering, or performing preventive maintenance, shall do that work in such a manner and use materials of such a quality, that the condition of the aircraft, airframe, aircraft engine, propeller, or appliance worked on will be at least equal to its original or properly altered condition (with regard to aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness).

(c) Special provisions for holders of air carrier operating certificates and operating certificates issued under the provisions of Part 121 or 135 and Part 129 operators holding operations specifications. Unless otherwise notified by the administrator, the methods, techniques, and practices contained in the maintenance manual or the maintenance part of the manual of the holder of an air carrier operating certificate or an operating certificate under Part 121 or 135 and Part 129 operators holding operations specifications (that is required by its operating specifications to provide a continuous airworthiness maintenance and inspection program) constitute acceptable means of compliance with this section.