L-19 Leaf spring installation

[Bruce Fenstermacher]

Hmmm. Joshua kind of reminds me of someone. Oh that's right, ME about 15 years ago driving George nuts holding a fire to all things said.

I was reading black and white and trying to make sense out of all the grey there is. And there is plenty of it. You might even be surprised that many things thought to be absolutely illegal in the Cessna 170 world are thought perfectly legal it the Piper Cub world.

Here is some more grey for you Joshua. I'd bet, in fact I'll do a survey this coming week at convention, that 9 out of 10 170s are sporting a "L-19" spring. I'd bet not a single owner ordered a L-19 spring. In fact they likely bought a 170 spring from a reputable supplier with PMA who made (or had made or bought from another reputable supplier) and the part had all the proper part number stampings on it. But the spring is thicker than the main leaf spring found on 170s when they left the factory. Most owners don't know the difference.

George seems to be able to get a 170 spring in the same thickness as original. I don't know where he gets it. Or when he last got one. Maybe he's using up new old stock. There are many many approved parts on aircraft of all sorts like the "L-19" spring. Not quite exactly the same as old, but suppose to be.

Does any of this make any spring legal? No. Doesn't make it illegal either.

Del has offered some good reading.

BTW does the thickness make the spring stiffer as you might suspect. Maybe not. Thicker does not necessarily mean stiffer.

[flyingredyeti]

Oh. You're trying to start an argument.
I understand now.

There is no approval for installing an L-19 main spring on a 170.
Nor is there approval for installing an L-19 eye bolt on a 170.

Continue your sermon.

You are inserting words into the regs, which makes a conversation with you impossible

Hey look, he can copy and paste too.

All you're doing is trolling the forum looking for a fight.

However, I will not administer medicine to the dead. If you are only interested in being right, find another sandbox.

There does seem to be some trolling on this thread, but it is not coming from me. I can't say for certain why you and David are so derogatory in your responses to a thread that I began with the intent on opening productive discussion, as I stated earlier. Just for the record, I am also not trying to "administer to the dead". If you, or anyone else chooses to willingly disregard the prescribed methods & current regulations, so be it. This conversation is meant to entice open-minded, well-intentioned owners and mechanics into sharing ideas-as I understand most of the forums on this site are intended.

Wingnut, I will read the articles you posted later tonight, and will respond then. However, in regards to your statement:

The above copy/paste does not contain the word "any"

, I would respond that it is clearly implied, as the statement: "Alterations of the following parts and alterations of the following types, when not listed in the aircraft specifications issued by the FAA, are airframe major alterations" is a generalization, such as:
Reciprocating engines convert linear motion into rotary motion,
or
Propellers and helicopter rotors are two forms of rotating airfoils.

There is even an exception in that first line of the FAA excerpt, as seen in the bold text above. To imply then the excerpt does not actually refer to any alteration to landing gear is argumentative, and would require some pretty concrete data to refute.

As I said, that is my initial response. I am always eager to educate myself further, and so I will read through your links, as promised.

In the meantime, I would appreciate a reduction in the combative replies, as that merely serves to discourage earnest parties from responding.

[Bruce Fenstermacher]

Joshua, where in the FAA specifications does it list a specific tail wheel spring?

[wingnut]

Del, thanks for the links both good reads. As stated the real problem as stated in the article is at the regional level where interpretations vary wildly. My local FSDO thinks that installing any avionics is a major alteration. I still haven't figured out how they came up with this after reading the FARs.

I have also found the "Northwest Mountain Region, Guide to Aircraft Alterations" a very good read, tho it looks like the FAA took it down off there site - I just happen to have a pdf version.

Praise be!!!! I just knew I had 'save and print' years ago. Apparently I just printed, or simply can't find the file. Just to clarify, this document is/was only regional policy, albeit very wise and welcome policy. Not regulatory by any stretch and not nation wide, much like the 'number of washers' policy. How many AN960-10 washers are on the bolt that attaches the flap to the actuator rod?
FAA has made strides in attempt to harmonize policy, but we aren't there yet. Improvements of existing regulations come when good and knowledgeable men (and women) continue working together, rather than accepting everything as is.
Thanks, I'll be saving the PDF this time.

[DaveF]

How many angels can dance on the head of an AN bolt?

[c170b53]

Wiggle words are there for a reason, some time in, might help in the understanding of why they are there, as to who put them there and when they are applicable or appropriate.
Joshua give it some time. Your new to this, you new here, enjoy the fact that you've found years of experience. Think about things. Trust me there's " no this is the only answer".

[bagarre]

Your opening posts had nothing to do with a constructive conversation and everything with you trying to show how much (little) you know about aviation regulations. It reminds me of the new boot recruit spouting off UCMJ regulations to fleet sailors. Nobody takes him seriously and they all hope he learns better.
If only the world was as simple as you understand it to be.

The fact of the matter is, there is more to aviation maintenance than is dreamed of in your title 14.
Sometimes, you need three washers or heaven forbid - 4 washers.
Other times, you use the parts that are available to make an airplane safe.

It's not even worth explaining to you because your past postings have shown you have no interest in learning...you already know everything.

[flyingredyeti]

Bruce, I may be wrong here, and I'll allow that (I am relatively new to aircraft maintenance after all), but wouldn't a tail leaf spring be covered under "landing gear"?

Jim, I have never claimed to know everything, nor to have the "only answer". In fact I opened this post with a question, not a statement. Yet, the only responses I have received thus far seem to simply disregard my ideas without offering any concrete data.

The question was, and is: Can anyone with experience in the matter, offer a mechanical justification or legal premise for installing an L-19 leaf spring assembly or the eyebolt, on the Cessna 170?

To all reading this: You want to debate the data I've presented? Fine. I've presented my knowledge of the facts, as I understand them. Please do the same from your perspective. Don't just tell me that from your experience, I'm wrong. That imparts very little. I want data, as do many others who may be reading this posts in the interest of present or future maintenance.

Teach 'em bad habits and that's all they'll know.

[bagarre]

I would argue the tailwheel main spring and 'eye bolt' are sufficiently similar in type, shape, materials and dimensions to the L-19 to have NO appreciable affect on weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness.
The only difference is a slight increase in thickness that has no affect on performance.

It does not change the gross weight. It does not change the CG range. It does not affect flight characteristics.

Also, the replacement is accomplished with accepted practices and elementary operations.

Therefore it is not a major alteration and requires only a log book entry.

You may need a 337 for the extra washer to properly torque the bolt tho.

[lowNslow]

My L-19 bolt is just the correct bolt with a ring welded on.

[flyingredyeti]

You know Bruce, I get it- the parts are similar, and the aircraft are related. However, that alone doesn't make the replacement legit, does it? To David, the factor I would be concerned with is added stress to the supporting structure. Many on here have related issues with the original Scott leafspring snapping. However, is that such a bad thing? I offer the parallel example of a shear bolt. It is designed to fail under a certain amount of stress in order to prevent more expensive damage to the driving mechanism in the event of overwhelming resistance.

If your leafspring snaps after so many hours, think of the stress that it has absorbed, and has thus prevented the airframe from suffering. Then consider the well-intentioned, mechanic who uses common sense and thinks: the L-19 spring is pretty close, it just requires a different bolt, and the bracket "pretty much" fits. Good news, it's thicker = it's stronger. A stronger spring, however, requires a heavier load to initiate compression. A heavier spring on a lighter load does not compress as easily as a lighter spring, and thus the loads imparted by the lighter structure are less capable of compressing the spring which does so to absorb the stress. Less compression = less shock absorption = more stress transmitted to the aircraft structure.

Lastly, Bruce I challenge you to offer me an example in aviation in which a heaver spring does not equal a stiffer spring.

Hey, I'm still open, but I'm not convinced on the basis of "it's pretty common".

[wingnut]

CHAPTER 2. MAJOR AND MINOR ALTERATIONS
200. GENERAL This chapter describes major alterations, minor alterations, and type design changes,
and gives examples of each. Type design changes, alterations, and modifications are all terms that
describe the same thing; changes to the design of the aircraft, aircraft engine, propeller, or
appliance as previously approved by the FAA.
201. MAJOR VS. MINOR ALTERATIONS
a. The definition of major alteration in FAR 1 is: “Major Alteration” means an alteration not listed in the
aircraft, aircraft engine, or propeller specifications-
(1). That might appreciably affect weight, balance, structural strength, performance, powerplant
operation, flight characteristics, or other qualities affecting airworthiness; or
(2). That is not done according to accepted practices or cannot be done by elementary operations.
b. This definition is reasonably clear except the meaning of “appreciably” and the phrase “...or other
qualities affecting airworthiness...”. In this regard, major alteration is considered to include any alteration
which as a result of malfunction or improper accomplishment could:
(1). Preclude continued safe flight and landing in any type operation for which the aircraft is approved;
or
(2). Adversely affect the safety of crew or passengers.
c. A minor alteration is defined as any alteration other that major.
202. DISCUSSION
a. For practical purposes, alterations and changes to type design have the same definition. Part 43,
appendix A, provides a listing of product alterations classified as major alterations. This list is not and
cannot be all-inclusive. Anyone proposing to alter or approve an alteration to a type certificated product
must make a judgement whether the alteration is major or minor. The definition in FAR 1 serves as the
foundation to make this judgement. As noted in paragraph 201, the difficulty in applying these
definitions is determining the meaning of “appreciable” and “other qualities affecting airworthiness”.
b. The list provided in this brochure (Chapter 4) gives examples of typical alterations that normally require
Aircraft Certification Office (ACO) evaluation and approval. This list includes alterations which may
require an STC for approval. These alterations are considered major alterations.
c. “Appreciable effect” and other “qualities affecting airworthiness” must be considered for the proposed
alteration. Webster’s 9th New Collegiate Dictionary definition of appreciable is “capable of being valued
or estimated”. Thus any effect that could be valued or estimated would be appreciable. Appreciable is
the value of such measurable effect.
d. Weight and Balance. Part 43, Appendix A(a)(xi), is definitive here. If an alteration results in an increase
in the maximum certificated weight or center of gravity limits of the aircraft, the effect is appreciable and
the alteration is major. If the alteration does not result in the weight or center of gravity limitations being
exceeded, or the mass distribution being changed, then it is a minor alteration with regard to weight and
balance. Mass distribution changes, such as addition of tip tanks or replacement of an engine with a
heavier engine, constitute mass distribution changes requiring engineering evaluation, even if maximum
weight limits are not exceeded.
Page 7 of 43
e. Structural strength. Generally, structural strength is determined by engineering analysis or tests. If
engineering analysis or tests are required to determine the effect of the alteration, then it is major.
However, if the structural alteration involved is performed according to standard practices (using
acceptable data that serves as the basis for an approval) and the structural strength of the product has not
been lessened or impaired by the alteration, then the alteration is minor with regard to structural strength.
Improving structural strength, in some cases, can have a detrimental effect on other structures, and must
be considered.
f. Performance. Aircraft performance is determined primarily by the difference in the aircraft’s available
thrust and the aircraft’s aerodynamic drag in a given flight condition. Any alteration to the aircraft,
aircraft engine, or propeller that may affect thrust, drag, or other changes that may affect the airflow over
the aircraft, is likely to affect performance. If experience or accepted guidelines have demonstrated that
the alteration (such as a small antenna installation) does not produce a measurable effect on performance,
then the alteration is minor with regard to performance.
g. Powerplant operation. The certification regulations, both for the engine and aircraft, require extensive
testing of the powerplant installation to verify its reliable operation within established operation
limitations on parameters such as temperature, RPM, pressure, carburetor icing, etc. Any alteration that
would require retest or engineering analysis to measure the effect and significance of reliable operation
would be a major alteration. This would include any alteration that could change airflow, either around
(cooling) or through (power) the engine. Such alterations might be changes to the cowling shape, cooling
airflow baffles, and induction and exhaust systems. Similarly, any change to fuel or oil systems that
could affect flow, pressure, or temperature (such as filter installations) would be major alterations.
Changes to powerplant controls are generally a major alteration because they require test and evaluation
to determine (measure) the effect.
h. Flight characteristics are similar to and closely related to aircraft performance. Any measurable change
to thrust or drag that affects performance is also likely to affect flight characteristics and requires
engineering flight test for evaluation. Thus, any alteration that may produce such an effect, such as a
change in the length or width of flight controls or power, is a major alteration.
i. Other qualities affecting airworthiness. This is an area where the examples of paragraph 201(b) could
be of particular use. Could the alteration as a result of malfunction or improper accomplishment
“preclude continued safe flight or landing” or “adversely affect the safety of crew or passengers?” This
could encompass areas such as landing gear, personal accommodations and human factors (pilots view,
cockpit arrangement, lighting adequacy, ventilation, emergency egress, shoulder harnesses, etc.), and
functioning installed equipment (navigation, communications, flight instruments, etc.).
The net effect to a weight change, for example, is totally dependent upon the location (flight station,
water line, etc.) not the actual weight of the article.
Therefore, a five pound weight change at station 186 on a Piper Cherokee 140, for example, may result in
a major alteration (or major change) as opposed to a five pound weight change at station 72, which may
result in a minor alteration.
j. It is important to understand that installation of a part with no prior approval (replacement part, new
piece of equipment, etc.) may constitute a major alteration and would need to be evaluated. This would
include installation of a replacement part made, for example, by another manufacturer than the one which
made the part on the original type design; or a different configuration of the same part, made by the
original manufacturer; or a new piece of equipment; or a part made by the owner/operator for installation
on his own aircraft. If the part in question was not manufactured under a PMA, or by the original type
certificate holder, it must have some sort of design approval as well as an installation approval.
Page 8 of 43
k. Manufacturers approved alterations. An exception to the previous discussion concerning the
determination of major versus minor are those alterations approved during the type certification process
and listed on the product specifications or type certificate data sheet. Regardless of the nature of the
alteration (e.g. optional engine or propeller), if it is listed on the specifications or type certificate data
sheet, installation of the alteration using the aircraft, engine, or propeller manufacturer’s instructions is
considered a minor alteration.
l. Negligible, which is often referred to with respect to such effects, is defined as “that [which] can be
disregarded; inconsiderable; trifling; of little importance or size”.

APPROVAL OF MAJOR AND MINOR ALTERATIONS
a. Major. Approval of major alterations to any type certificated product (aircraft, aircraft engine, or
propeller) is accomplished in three ways.
(l). Type Design Change. The TC holder may submit a change to the type design for approval by the
FAA. If there are significant differences between the original product and the altered one, the type
certificate is amended in accordance with FAR 21, Subpart D. If the FAA has granted the TC holder a
delegation option authorization (DOA), the TC holder may approve changes to the type design.
(2). Supplemental Type Certificate. Any person may apply for an STC to make a major alteration to
a type certificated product. The STC approval process is normally used for major alterations that
require detailed engineering analysis. FAR 21, Subpart E, prescribes the requirements. The specific
procedures are available from any Aircraft Certification Office (ACO) in AC 21-40.
(3). Field Approval. Any person may apply for field approval of a major alteration to a type
certificated product. Field approvals are normally used for major alterations that do not require a
detailed engineering analysis. A field approval is comparable to an STC.
b. Minor. Minor alterations to a type certificated product are accomplished by any appropriately qualified
and certificated person (mechanic, repair station, air carrier) using data acceptable to the Administrator.
Approvals for return to service are accomplished using a log book entry in accordance with FAR 43.5.

404. ALTERATIONS REQUIRING ACO ENGINEERING APPROVAL
Items (a) through (o) in the following list of typical alterations will most likely require engineering
approval, and often require an STC. Items in (p) do not normally require an STC but will usually require
ACO engineering assistance.
a. Increase in gross weight and/or changes in c.g. range.
Page 13 of 43
b. Installation or relocation of equipment and systems or changes which may adversely affect structural
integrity, flight or ground handling characteristics of aircraft. For example, engines and/or propellers of a
different make or model not listed in the type certificate data sheet, or the relocation or change of throttle
levers, flap controls, and similar, alterations.
c. Any change (alteration) of movable control surfaces which may adversely disturb the dynamic or
static balance, alter the contour, length, or width, and/or make any difference (plus or minus) in the
weight distribution, and any addition of control surfaces not contained in the original type design.
d. Change in control surface travels (reduced travels or travels outside approved limits), control system
mechanical advantage, location of control system component parts, or direction of motion of controls.
e. Changes in basic dimensions or external configuration of the aircraft, such as wing and tail plan-form or
incidence angles, canopy, cowlings, contour or radii, or location of wing and tail farings.
f. Changes to landing gear, such as internal parts of shock struts, length, geometry, or brakes and brake
systems.
g. Any change to engine cowling and/or baffling which may adversely affect the flow of cooling air
and/or manifolding.
h. Changes to primary structure which may adversely affect strength, flutter, or vibration characteristics.
i. Changes to systems which may adversely affect aircraft airworthiness such as the relocation of exterior
fuel vents, use of hydraulic components, tube material and fittings not previously approved or use of new
fusible hydraulic plugs.
j. Changes to oil and fuel lines or systems which may adversely affect their operation, such as a new type
of hose or hose fittings, changes in fuel dump valves, new fuel cell sealants, new fuel or oil line
materials, and new fuel or oil tanks and system components.
k. Any change to the basic aircraft engine propeller controls or operating limitations, and changes to
engine adjustments and settings having an effect on power output.
l. Changes in a fixed fire extinguisher or detector system which may adversely affect the system
effectiveness or reliability, such as relocation of discharge nozzle or detector units; use of new or
different detector components in new circuit arrangements; deletion of detector units or discharge
nozzles; change in extinguishing agent or decrease in amount of extinguishing agent.
m. Changes which do not conform to the minimum standards established in a Technical Standard Order
under which a particular aircraft component or appliance is manufactured.
n. Alterations to TSO’d equipment; (e.g., communication and navigation, avionics, seats, wheels, tires,
etc.). Any change to a TSO’s item invalidates the TSO approval.
o. Changes to aircraft structure or cabin interior of aircraft that may adversely affect evacuation of
occupants in any manner or change the type certificated seating configuration, i.e. including seat pitch or
passenger service unit location.

[wingnut]

Bottom line is this, the subject 'alteration' of this thread is up for the installing mechanics judgement. It is an important judgement. If a mechanic is genuinely interested in NOT bankrupting the industry that he wants to specialize in, he will read the regulations as they are meant to be read. Be safe, not stupid!
Both of the parts in discussion, the bolt and the leaf, are approved for installation on a type certified product per FAR 21. Subsequent PMA's cover the rest. As for installation of these parts on an aircraft that did not leave the factory with the exact same part number, I SAY MINOR ALTERATION..........because the definition has been read, understood, verified, and explained too many times already.

Joshua,
I appreciate the attempt at irrigating our minds with your vast reservoirs of knowledge. It seems a noble cause. But you are not listening. If you were, I'd be more inclined to share some wisdom with you, but you are steadfast in your belligerence. Please, study up before you choke up. It really sounds like you are passionate about this A&P ticket along with other things aviation. I almost want to beg you to dig deeper in knowledge before you dig yourself into a hole, but this present day GA world doesn't need you as you are. We need free thinkers that are capable of doing things right and going through the correct channels if something needs changed. We do not need book smart. We need people that think outside the box if these aircraft are to outlast one more generation. Outside the box = FAR's are the aircraft owners friend if you will allow them to be. If you choose to read one sentence of one FAR, you will be doing your customers an historic injustice.

[bagarre]

The L-19 has the same weight characteristics as the 170. It has the same fuselage for all intents and purposes. It also has the same tailwheel attach bracket as the 170. This is not a case of an overly rigid system transferring stress to other members. It is effectively the same part.
The spring failing has nothing to do with weakness or stress in the system. Is has to do with the next spring in the pack wearing a stress riser in the main spring. This happens with the L-19 as well. That has nothing to do with the replacement and no one is claiming a longer wear life with the L-19 spring.
Your argument is theoretical and precludes common sense. The reasoning I presented was good enough for me. It was good enough for the mechanic working beside me at the time and has been good enough for two different IAs that have performed annual inspections on my airplane. I don't really care if it's not good enough for you.

Again. If you're not comfortable with this reasoning, you are more than welcome to hire a DER and have him prove it out for you on your aircraft. Then take that data to the FAA and have them say "Of course" and get a field approval (or hopefully they will say this is Minor and not further erode common sense)

[Bruce Fenstermacher]

Joshua, I would never try to prove something was legal because it is common.

Thicker does not mean stronger. A different temper is all it would take to change the spring rate of a thicker spring to being softer than a thinner harder spring. As noted the "L-19" also snaps on a 170. Mine did sitting at the tie down. I don't know off hand of an steel spring example in aviation but I'll bet there is.

The question was, and is: Can anyone with experience in the matter, offer a mechanical justification or legal premise for installing an L-19 leaf spring assembly or the eyebolt, on the Cessna 170?

A spring that is the thickness of the original may not be available. So you use the thicker spring sold under PMA as a replacement spring rather than try to reverse engineer the original spring and make an owner produced part. BTW how would you know a spring sold under PMA that looked like the original actually meet the same standard? You trust the same people selling the larger spring?

As for the bolt, it starts life as a regular AN bolt correct for the installation. It is modified with a ring which makes tying down your airplane more convenient. Presumably the bolt is brought back to tolerance of the original AN bolt unmodified as it is sold as an aircraft part for the same purpose. So in essence the ring is a minor modification to the standard hardware.