When to change a tire

[Colonel Sanders]

it does seem odd that they (or at least Bombardier) seem to let you run their planes with bald tires

Obviously the aircraft manufacturers know nothing
about how to operate their aircraft.

[flatface]

Deleted

[CpnCrunch]

it does seem odd that they (or at least Bombardier) seem to let you run their planes with bald tires

Obviously the aircraft manufacturers know nothing
about how to operate their aircraft.

Sometimes they don't, as you yourself have pointed out in regards to the breather tube.

[Colonel Sanders]

I do not recall ever reading about tire limits with regard to hydroplaning

Me neither.

[CpnCrunch]

I do not recall ever reading about tire limits with regard to hydroplaning

Me neither.

It's more to do with braking effectiveness in the wet, rather than hydroplaning (which isn't really affected by tread wear). It's CS who keeps bringing up the straw man of hydroplaning for some reason.

http://ntrs.nasa.gov/archive/nasa/casi. ... 012763.pdf

As you can see in fig 20, the biggest difference seems to be in deep water (braking is about 3 times worse with slick tires, as far as I can see). In shallow water, there doesn't seem to be as much difference (fig 10).

[pelmet]

On the heavy jets I worked on, the MIM had a section with 20 pages of tire inspection limits. There are so many possible tread wear patterns and damage patterns that there is no simple rule. This is just what I have observed over the years.

I called a maintenance guy over during the walkaround recently due to what appeared to be a deep sharp cut in a tire. Was told that it was within limits even though cord had been cut. Apparantly was not cut below the groove level of the tread. Looked nasty though.

[mingshiyaaun]

Change after every 2yrs or 100k run AND before winter starts

[torquey401]

Interesting video on this subject.

[torquey401]

Was told that it was within limits even though cord had been cut.

Assuming the AMM has specific data in this case. If not:

From Goodyear:
Tread Cuts
Inspect tread for cuts and other foreign object damage and mark with crayon or chalk. Follow the removal criteria below:
1. Follow specific cut removal criteria from the aircraft manual, or tire cut limits on the tire sidewall when available.
2. When specific cut removal criteria are not available use the following Goodyear removal criteria: any cut into the
casing plies on bias tires, any cut into the belt package on radial tires, any cut which extends across one or more
rubber tread ribs to the fabric, rib undercutting at the base of any cut.

From Michelin:
8.10. FOD (Foreign Object Damage) or Tread Cuts
8.10.1. Description: Localized tread cut or damage from a object.
8.10.2. Cause: Rolling a tire over foreign objects on the runway or taxiway. Impact from an
external object or source.
8.10.3. Remove tires from service if:
8.10.3.1. Cuts, embedded objects, or other injuries expose or penetrate the reinforcing
plies (bias) or protector ply (radial).
8.10.3.2. Cuts, embedded objects or other injuries that do not expose or penetrate the
reinforcing plies (bias) or protector ply (radial) if:
• A cut extends entirely across a tread rib (any depth).
• A round object is greater than 9.5 mm (0.375 in).
8.10.3.3. Refer to Figure 517.

[flatface]

Deleted

[GyvAir]

Thanks for posting that video, torquey401.. interesting to watch.

I'm sure even CS couldn't refute information presented in a video narrated by a man named Brick Ryder, backed by the stylin' tunes of a full orchestral educational film soundtrack!

[ChallengerDan]

Every operator I have worked so far usually uses grooves as wear criteria when doing routine maintenance. The idea is that removing a tire when you are at 1/32 from groove base instead of actually waiting for rejection criteria point is usually more cost effective than incurring delays because someone realizes during a walk-around that one tire is finished.

This method is not perfect, but is a good rule of thumb.

Why it is not perfect?
1- Well technically you are not using all your money's worth.
2- Some aircraft will wear to no grooves without showing any chord (Classic Dash8, for example)
3- Some aircraft will wear to chord before getting to any groove base (CRJ900 is known for that)
4- You can run the risk of not being able to retread the tire, which could incur some costs (core exchange)

Now when tire wear is inspected on the flight line, with the aircraft loaded, boarded, and fuelled, we will, from a maintenance perspective, try to use all the waivers from the AMM. Common sense and experience might also be used, but then your mileage may vary.

Corporate flight department usually change tires more frequently, as from a maintenance perspective the aircraft might be away from the base on a long international deployment, so anything less than 1/16 usually gets replaced, unless the aircraft has a known and predictable sched.

I've seen operators that had a specific number of plies exposed to incur rejection (Egyptair A300B6 for example), but IIRC it needs to be specified explicitly on the tires or the manual.

Failures do occur, but are rather rare considering the intended use, and experience has shown that tires worst enemies on highly loaded transport category aircraft is under-inflation, hot temps and long taxi runs.

As some have pointed, the actual limits are in the AMM or the Tire Manufacturers docs and CMM.

And to CS's defence, it does happen that the stars line up and an aircraft will have all mains pretty worn, and I have yet come accross a write-up that aircraft was hard to control on landing because of worn tires. And Pilot can be whiney %$#?$! Usually problems are a result of braking/Antiskid issues and not related to tire wear. I could be wrong, though.

[Colonel Sanders]

For local use only, on my aircraft, I like to see cord before
I pull the tire. The tires I run are 6 ply Goodyear Flight
Custom III which have two white outer plies, and 4 red
inner plies, which pretty much tells the story.

I don't have a picture with me right now, but after pulling
a pretty scummy looking tire, it's educational to take a very
sharp knife and cut the cross-section of the tire, where
the cord was showing - where the tire visually was at it's
worst.

With the 6 ply Goodyears, you would be amazed at how
thick the rubber is, and how many plies are left when cord
shows.

[GyvAir]

For local use only, on my aircraft

Caveat duly noted and not disputed.

I like to see cord

I can assure you that the owners of corporate flight departments do not like to see the cord on a tire installed on their Xmillion dollar equipment.
I'm not going to put myself in the position of having to explain to an owner that to save the company $50, I chose to leave a "scummy looking tire" installed until it no longer met bare minimum airworthiness limits in order to get a dozen more cycles out of it.
For one thing, it simply looks bad. You're not going to go around in a shiny new suit and threadbare socks, why would you go around with threadbare tires on your shiny ride?
From a safety point of view, no, a 10 ply tire isn't likely to fail because some cord is showing. And true, the likelihood of the reduced braking performance and directional control isn't likely to cause an accident on its own. Everyone who's ever taken an afternoon course on accident prevention knows though, that accidents are rarely the result of a single failure. They are almost always the result of a chain of events or factors. I don't see any acceptable reason to knowingly set up a flight crew with one of those negative factors.

[Colonel Sanders]

it simply looks bad

There it is!

a 10 ply tire isn't likely to fail because some cord is showing

Do us all a small favour. After you swap out one of your 10 ply tires
that looks bad, cut the tire across the worst part of it - which is not
going to be easy - and post a picture of how much rubber was left.

The point I am trying to make (to pilots) is that just because something
might look bad, doesn't mean it is bad. And just because it looks good,
doesn't mean it is good. Cosmetics aren't everything.

All too often, pilots will "buy a paint job". Shiny paint on an airplane with
lots of trouble lurking underneath. A friend of mine and his wife are dead
now, because he bought a shiny airplane with a cracked spar from a
previous serious accident. Broke up in flight.

Another friend of mine was all worried because the paint on the fabric
of an airplane he was buying was dull. But the paint had no cracks in
it. I told him that it would shine up like a million bucks with a little
rubbing, and it did.