This one has been racking my mind for years. I see literally tons of information about field approvals of "unapproved" tire size on aircraft on the interwebs....

So: My question is, for an aircraft that was certificated under CAR 3, why are people seeking (and the FAA granting) field approvals for (generally) larger tires? Now hear me out...

The FAA states that for an aircraft to be considered to be airworthy, it must meet its original type design or properly altered state. This would logically lead to the TCDS, or an STC for the proper alteration. That being said, many of these aircraft (Cessna 180/185 for example) do not have a tire make/model/size called out in the TCDS. That would direct the A&P/IA to the certification basis of the aircraft for approved sizes. The TCDS states that CAR 3 is the certification basis, and upon some research in the CAR's one will find that any size tire is approved, so long as that tire is of an approved type for aircraft (TSO).

Furthermore, AC 23-17C, section 23.733 (Tires) cites that the corresponding rule is CAR 3.362. 3.362 Tires. A landing gear wheel may be
equipped with any make or type of tire, provided that the approved tire rating is not exceeded under the following conditions: (a) Load on main wheel tires equal to the airplane weight divided by the number of wheels, (b) Load on nose wheel tires (to be compared with the dynamic rating established for such tires) equal to the reaction obtained at the nose wheel, assuming the mass of the airplane concentrated at the center of gravity and exerting a force of 1.0g downward and 0.31g forward, the reactions being distributed to the nose and main wheels by the principle of statics with the drag reaction at the ground applied only at those wheels having brakes. When specially constructed tires are used to support an airplane, the wheels shall be plainly and conspicuously marked to that effect. Such marking shall include
the make, size, number of plies, and identification marking of the proper tire. Note: Approved ratings are those assigned by the Tire and Rim Association or by the Administrator.

So, BCP.org, what are your opinions about this logic and what am I missing? Maintenance and alteration of aging aircraft is inherently a grey area sometimes and I seem to keep making this area more grey for myself.

Only problem I've encountered is getting a mechanic that believes in this thought process enough to give their signature.

Nothing grey about your analysis. Black and white. I showed it to my IA and he nodded. At the risk of another posting censure by admin I'll leave it at that.

About the same conclusion I've arrived at. Looks like a trip down FSDO lane is in order to get a final ruling from the Administrator himself. I'll post to let you guys know what comes of it when it happens.

S.patJ3 wrote:....The FAA states that for an aircraft to be considered to be airworthy, it must meet its original type design or properly altered state. This would logically lead to the TCDS, or an STC for the proper alteration. That being said, many of these aircraft (Cessna 180/185 for example) do not have a tire make/model/size called out in the TCDS. ......

Yes and no.
The TCDS #A-799 for my C170 had a very comprehensive list of approved equipment.

http://rgl.faa.gov/Regulatory_and_Guida ... Rev_55.pdf

For example, item 201 lists approved MLG wheel / brake assemblies.
Item 202 lists approved MLG tires.
Item 204 lists approved tailwheel assemblies.

TCDS #5A6 for my Cesna 180 doesn't have this detailed list of approved equipment.
But, the factory equipment list for my particular airplane (issued along with the factory W&B info) does, in the same format.
Item 201 is MLG wheels & brakes.
Item 202 is MLG tires
Item 204 is tailwheel assembly..
It doesn't call out approved models but it does call out approved MLG tire sizes: 600x6- 6 ply rating and 800x6-4 ply rating.

It's very subjective, and you need to really read through your TCDS and certification criteria. I will use my own plane (1957 C182) as an example. My TCDS is 3A13, and it was certified under the older CAR Part 3 criteria. Airplane types that began life prior to Feb 1 1965 were certified under CAR3 and likely continued under those standards, 1965 and on would be FAR 23.

Per my TCDS, I have no requirements whatsoever for equipment other than engine, prop hub/blades, governor, and spinner. Literally everything else is optional unless CAR3 mandates it. Mods to those required pieces will require STC, otherwise we can simply defer to what CAR3 says we need to do. What's interesting is that the older C170 TCDS linked above is far more prescriptive in terms of equipment required, CG envelope, and so on. Not sure what changed from the 40's to 50's where Cessna would simplify the TCDS so much, but it is what it is.

Here is what CAR3 says about tires:
WHEELS AND TIRES
§ 3.361 Wheels. (a) Main landing gear
wheels (i.e., those nearest the airplane center of
gravity) shall be of an approved type.
(b) The rated static load of each main wheel
shall not be less than the design weight for
ground loads (§ 3.242) divided by the number of
main wheels. Nose wheels shall have been tested
for an ultimate radial load not less than the
maximum nose wheel ultimate load obtained in
the ground loads requirements, and for
corresponding side and burst loads.
§ 3.362 Tires. A landing gear wheel may be
equipped with any make or type of tire, provided
that the approved tire rating is not exceeded
under the following conditions:
(a) Load on main wheel tires equal to the
airplane weight divided by the number of wheels,
(b) Load on nose wheel tires (to be
compared with the dynamic rating established for
such tires) equal to the reaction obtained at the
nose wheel, assuming the mass of the airplane
concentrated at the center of gravity and exerting
a force of 1.0g downward and 0.31g forward, the
reactions being distributed to the nose and main
wheels by the principle of statics with the drag
reaction at the ground applied only at those
wheels having brakes. When specially
constructed tires are used to support an airplane,
the wheels shall be plainly and conspicuously
marked to that effect. Such marking shall include
the make, size, number of plies, and identification
marking of the proper tire.
Note: Approved ratings are those assigned
by the Tire and Rim Association or by the
Administrator.


So, per my TCDS and CAR3, I could literally put any "approved" tire on my plane that I wanted if it supported the weight. Now that doesn't mean it'll fit on the nose, and modifying that fork requires STC or field approval. The Airglas STC also allows for various tire sizes, however per my interpretation of TCDS and CAR3 I could legally go with anything that fits. Now what "approved" means may be more vague, particularly considering the vintage of these regulations.

If your TCDS prescribes certain wheels or tires then that will supersede CAR3/FAR23, and will be limited to those components unless you have an STC allowing deviation (e.g. Airglas fork STC) or obtain a field approval to do it.

(Now I am not a lawyer, but I did stay at a Holiday Inn Express once and have spent a while reading these documents...)

colopilot wrote:It's very subjective, and you need to really read through your TCDS and certification criteria. I will use my own plane (1957 C182) as an example. My TCDS is 3A13, and it was certified under the older CAR Part 3 criteria. Airplane types that began life prior to Feb 1 1965 were certified under CAR3 and likely continued under those standards, 1965 and on would be FAR 23.

Per my TCDS, I have no requirements whatsoever for equipment other than engine, prop hub/blades, governor, and spinner. Literally everything else is optional unless CAR3 mandates it. Mods to those required pieces will require STC, otherwise we can simply defer to what CAR3 says we need to do. What's interesting is that the older C170 TCDS linked above is far more prescriptive in terms of equipment required, CG envelope, and so on. Not sure what changed from the 40's to 50's where Cessna would simplify the TCDS so much, but it is what it is.

Here is what CAR3 says about tires:
WHEELS AND TIRES
§ 3.361 Wheels. (a) Main landing gear
wheels (i.e., those nearest the airplane center of
gravity) shall be of an approved type.
(b) The rated static load of each main wheel
shall not be less than the design weight for
ground loads (§ 3.242) divided by the number of
main wheels. Nose wheels shall have been tested
for an ultimate radial load not less than the
maximum nose wheel ultimate load obtained in
the ground loads requirements, and for
corresponding side and burst loads.
§ 3.362 Tires. A landing gear wheel may be
equipped with any make or type of tire, provided
that the approved tire rating is not exceeded
under the following conditions:
(a) Load on main wheel tires equal to the
airplane weight divided by the number of wheels,
(b) Load on nose wheel tires (to be
compared with the dynamic rating established for
such tires) equal to the reaction obtained at the
nose wheel, assuming the mass of the airplane
concentrated at the center of gravity and exerting
a force of 1.0g downward and 0.31g forward, the
reactions being distributed to the nose and main
wheels by the principle of statics with the drag
reaction at the ground applied only at those
wheels having brakes. When specially
constructed tires are used to support an airplane,
the wheels shall be plainly and conspicuously
marked to that effect. Such marking shall include
the make, size, number of plies, and identification
marking of the proper tire.
Note: Approved ratings are those assigned
by the Tire and Rim Association or by the
Administrator.


So, per my TCDS and CAR3, I could literally put any "approved" tire on my plane that I wanted if it supported the weight. Now that doesn't mean it'll fit on the nose, and modifying that fork requires STC or field approval. The Airglas STC also allows for various tire sizes, however per my interpretation of TCDS and CAR3 I could legally go with anything that fits. Now what "approved" means may be more vague, particularly considering the vintage of these regulations.

If your TCDS prescribes certain wheels or tires then that will supersede CAR3/FAR23, and will be limited to those components unless you have an STC allowing deviation (e.g. Airglas fork STC) or obtain a field approval to do it.

(Now I am not a lawyer, but I did stay at a Holiday Inn Express once and have spent a while reading these documents...)

But as Hotrod pointed out above, your airplane MAY have a factory equipment list that "approves" certain sizes of tires. Most of the Cessnas I've flown do.

MTV

S.patJ3 wrote:... Looks like a trip down FSDO lane is in order to get a final ruling from the Administrator himself....

FSDO lane?!

Respectfully, instead I suggest asking the folks the Administrator asks: the AGC (Office of the Chief Counsel), who, among other duties "...also interpret the FAA's regulations...." https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/

You may also search for interpretations via key word (try: field approval) at
https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/Interpretations/

Note the AGC responds in writing to inquiries.

mtv wrote:But as Hotrod pointed out above, your airplane MAY have a factory equipment list that "approves" certain sizes of tires. Most of the Cessnas I've flown do.

MTV

Yeah, we're saying the same thing. If you have that list defined then you need to comply, or obtain an STC/field approval that permits legal deviation. If you don't have that list then certification standards (CAR 3 in this case) should apply as the catch-all for everything the TCDS didn't explicitly spell out.

colopilot wrote:

mtv wrote:But as Hotrod pointed out above, your airplane MAY have a factory equipment list that "approves" certain sizes of tires. Most of the Cessnas I've flown do.

MTV

Yeah, we're saying the same thing. If you have that list defined then you need to comply, or obtain an STC/field approval that permits legal deviation. If you don't have that list then certification standards (CAR 3 in this case) should apply as the catch-all for everything the TCDS didn't explicitly spell out.

At what point does the parts book come in to play? For example, if your parts book lists 2 options of tire sizes. Does this not come into consideration before hitting the CAR3 reg?

My Tdata subscription that I use as a library as a requirement of my IA certificate includes as a convenience a copy of the Cessna 180 TC revision 34 which includes the equipment list similar to what is included with the Cessna 170 TC. This applies to the 180 through 180F. The tires listed are item 202 (a) 6.00x6 6 ply tube type, 202 (b) 8.00x6 4 ply tube type, 202 (c) 7.00x6 4 ply tube type, and 202 (d) 6.00x6 6 ply tubeless type. Please note that these are for the 180 through the 180F so the maximum gross weight is 2650 pounds for the heaviest of these models.

One question that comes to mind, for those airplanes modified with wing extensions which increase the gross weight to 2950 pounds are higher load rated (ply) tires requires?

Tim

A1Skinner wrote:At what point does the parts book come in to play? For example, if your parts book lists 2 options of tire sizes. Does this not come into consideration before hitting the CAR3 reg?

Ahh, good callout. It may, this is where that FAA interpretive writeup will be useful clarification. If you wanted to get really intricate you could suggest you needed the exact same part number, except that nobody actually follows that number in real life (for old planes the tire p/n probably isn't made any more) - they use an equivalent approved tire. So one could argue that since the part number is irrelevant anyway, the size too may not matter if not explicitly TCDS'd. However the parts manual will specify a size of tire, the FAA could also argue that while p/n is unimportant the size/ply definitely are.

I hope this question makes it into the information request.

bat443 wrote:One question that comes to mind, for those airplanes modified with wing extensions which increase the gross weight to 2950 pounds are higher load rated (ply) tires requires?

One would think so. If not a matter of "letter of the law" regs, then at least as a matter of physics. You don't want 2700lbs worth of tire on a 2950lb airplane.

my original post should have said per the STC. Sorry

Tim

I think that you may be looking at this the wrong way. Far part 43 specifies changes to landing gear as a major alteration if it is not on the faa-approved aircraft specifications. So the lack of information on a tcds or equipment list does not constitute the approval to change wherever you want. Instead you need to look for specifically approved data. Approved data will be in the form of tcds, manufactures equipment list, an STC or an FAA field approved 337 form. There is some other options also but those are the most common. Mechanics and IAs do not approve data they only approve for return to service based on work performed in accordance with approved data. So the challenge is not finding a mechanic that will buy off on your line of thinking the challenge is coming up with FAA approved data.

colopilot wrote:....Per my TCDS, I have no requirements whatsoever for equipment other than engine, prop hub/blades, governor, and spinner. Literally everything else is optional unless CAR3 mandates it. Mods to those required pieces will require STC, otherwise we can simply defer to what CAR3 says we need to do. .....

A couple years ago, I decided that I wanted to install a Garmin G5 electrnic horizon on my 1953 C180.
(this is before the STC'd version came out).
I wrote an email to the local FSDO, attention airworthiness dept, and told them what I wanted to do.
In short, I said that my understanding was that since my airplane was CAR3 certified, I could do that.
No TSO requirement under CAR 3 etc.
They emailed back and said fine, just have a licensed mechanic do the installation, log it, and revise the W&B.

When I went to actually put in the G5, I showed the email exchange to my IA buddy who was gonna inspect and document the installation.
He decided that he needed to run it by his maintenance inspector. (another person at the same FSDO)
He got an email back that (although he didn't name it) quoted the FAA's policy statement about replacing vacuum horizons with electronic horizons, in particular the part that said it needed to have a back-up battery.
I didn't really want to buy one of those, they're $150,
but I figured if that's what it took to make everybody happy it was well worth the price.

So same FSDO, but two different inspectors with two different opinions.

I'm an IA, and I agree with the op's logic. Changing tire size alone does not constitute a major alteration, therefore does not require a field approval or STC.

The difference is that the C170 was built with an Aircraft Specification Sheet (A-799) which required an equipment list rather than a TCDS like the 180 (5A6).

Karmutzen wrote: At the risk of another posting censure by admin I'll leave it at that.

I have a generally positive recollection of your participation here, so I don't recall what it was all about. Apologies if you were made to endure any disapproval.

bat443 wrote: My Tdata subscription that I use as a library as a requirement of my IA certificate includes as a convenience a copy of the Cessna 180 TC revision 34 which includes the equipment list similar to what is included with the Cessna 170 TC. This applies to the 180 through 180F. .....

THis was news to me.
The most recent version of TCDS 5A6 is revision 68.
Under "data pertinent to all models",
just before note 1, I did find a reference to rev 34:
"The equipment portion of Aircraft Specification 5A6, revision 34, or Cessna publication TS2000-12 should be used for equipment references on all aircraft prior to the Model 180G. Refer to the applicable equipment list for the model 180G and subsequent models."

I tried googled TCDS 5A6 revision 34,
also Cessna publication TS2000-12.
No luck with either one.

Bat443, any way you could scan me a copy of that equipment portion?
Or scan one for the BCP "knowledge base"?

MBpilot88A wrote:..... What's interesting is that the older C170 TCDS linked above is far more prescriptive in terms of equipment required, CG envelope, and so on. Not sure what changed from the 40's to 50's where Cessna would simplify the TCDS so much, but it is what it is.
-----------The difference is that the C170 was built with an Aircraft Specification Sheet (A-799) which required an equipment list rather than a TCDS like the 180 (5A6).

Whether they call it an aircraft spec sheet or a TCDS,
it was sure nice to have all that information spelled out as on the 170 document.
Not included in the C180TCDS,
instead there's 7 pages worth (!!) of information about required placards.