Fusible plugs - aircraft wheels

As airport firefighters, we are concerned about explosive failure of aircraft wheels during a landing gear fire. Wheels are usually equiped with fusible plugs that will release nitrogen pressure when the wheels will overheat. It is my understanding that those thermal pressure release devices are venting towards the inner part of the split rim wheel and are therefore not such a projectile threat. I suspect that the danger with aircraft wheels (in terms of explosive failures) lies in the design of the wheels (split rims) and in the corrosion cracking of the retaining bolts of the wheels. Could anyone has any information on those fusible plugs, their designs, their locations and if any of you had witnessed an aircraft wheel explosive failure ? Thank you.

Hey Ottawa, great questions!

I never have been around during a tire/wheel explosive failure. However, I was on standby for an AV-8B Harrier flight test operation when the fuseable plug released pressure due to a hot brake situation. The scream of high pressure nitrogen escaping through the small vents scared the crap out of me. It’s a sound I’ll never forget! :eek:

Fuseable plugs have several channels (vents) arranged circumferentially around the wheel and filled with a solder-like material that is normally hard, but which turns to liquid at it's peak temperature and flows out of the channels allowing the nitrogen to exit the tire.

Here's a photo of a fuseable plug...note the vents. (http://www.arff.info/images/757-5.JPG)
I get a better photo next time.

On the opposite side is the wheel is the pressure gauge. (http://www.arff.info/images/757-6.JPG)

If you look close, you can see how there both arranged on the wheel. (http://www.arff.info/images/757-4.JPG)

These photos are of a Boeing 757. (http://www.arff.info/boeing-757.htm)

I hope this helps.

Hello Admin;

I would like to mention that the picture of the so called "fusible plug" is not a fusible plug. It is an overinflation pressure relief (OPR) valve. An OPR valve is a device similar to that shown on your picture. It is included in many wheel assemblies to limit the pressure in the wheel/tire assembly. However, certain older wheels do not include this valve. If the pressure in the wheel exceeds a predetermined value, a disk in the OPR valve will rupture, allowing the gas to escape, thus reducing the pressure in the wheel before it can fracture. After the disk ruptures, the gas in the wheel will exit through the OPR valve. The valve is designed so that when the disk ruptures, the gas will exit from the wheel faster than it can be supplied from the pressure source.

On newer wheels the fuse plugs are usually located on the inboard side and there are usually three or four compare to one OPR valve per wheel which is generally located diametrically opposed to the inflation valve.

Thank you.

Hey Ottawa,

You can call me Don. I have to log in as Admin to perform maintenance on this board. Sometimes I forget to change back.

Thank you for the information. I have been follow the discussions at the links below:


http://www.airdisaster.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=14&t=000157

http://www.airdisaster.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=14&t=000158

http://www.airmech.co.uk/ubb/ultimatebb.php?ubb=get_topic;f=36;t=000064

I am indeed the one that posted the threads that you did mention earlier on. I finally obtain the information I wanted from Boeing. You will find below a link to a technical publication from Boeing treating the subject of OPR's. Look into the January 1999 magazine and then go to wheel servicing section.


http://www.boeing.com/commercial/aeromagazine/aero_07/archive.html

Thank you very much for your assistance.

hey guys

though i would get in on this one, most everything flying in here has fuse plugs a few of the smaller turbo props don't.

as far as explosive failure, i have seenand heard a couple on fighters, most of the commericals one i have been on tend to either go boom or hiss real loud.

we a B747 abort a couple years ago an blew out 10 of 16 tires and set the left outer boggie on fire. some hissed and some went boom but most of the booms were the tires failing. yep it was a long night.

dk