Does an engine overhaul require a new weight and balance and FAA form 337?

[simon]

I *think* I know the answer, but I would prefer views from current certified A&P(s). Certainly a reference from the relevant FAR.

A friend who just had an overhaul has neither. I queried him on the new W&B. In turn, he asked the mechanic, who in turn, shunned the idea. To me, with little experience in these matters, but having seen W&B entries in rental aircraft for as little as a new GPS, it seemed odd. I haven't looked up the FARs. Is it required? I should also mention that the engine that came out was a 520 whereas the overhauled unit that went in is a 550.

As I said, I *think* I know the answer, but I'd like a reference.

[bosshawk]

Simon: you are mixing apples and oranges.  An engine overhaul assumes that you simply(and expensively)overhauled the existing engine.  No 337 nor W and B needed.  Replacing a 520 with a 550 likely requires an STC and a new W and B.  A 550 weighs more than a 520.  I can't quote the applicable FAR, maybe someone else can.

As an example: I overhauled the cylinders on my IO-470 last Fall.  It didn't require anything other than a logbook entry and a description of what was done to the cylinders.  That is a partial overhaul.

I am sure that there are A and Ps on this forum: let them explain it better.  There are mechanics around who simply don't believe in doing the proper paperwork.

[SarDragon]

Here's what I found in the FARs. This is an excerpt, and may not completely address the situation.

Appendix A to Part 43—Major Alterations, Major Repairs, and Preventive Maintenance

(a) Major alterations —(1) Airframe major alterations. 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:

(xi) Changes to the empty weight or empty balance which result in an increase in the maximum certificated weight or center of gravity limits of the aircraft.
*****
(2) Powerplant major alterations. The following alterations of a powerplant when not listed in the engine specifications issued by the FAA, are powerplant major alterations.

(i) Conversion of an aircraft engine from one approved model to another, involving any changes in compression ratio, propeller reduction gear, impeller gear ratios or the substitution of major engine parts which requires extensive rework and testing of the engine.
*****
Appendix B to Part 43—Recording of Major Repairs and Major Alterations

(a) Except as provided in paragraphs (b), (c), and (d) of this appendix, each person performing a major repair or major alteration shall—

(1) Execute FAA Form 337 at least in duplicate;

It looks to me like the paperwork is required.

[PHall]

If it's a straight overhaul, i.e. worn parts replaced with new parts, there should not be any weight change and a W & B is not required.

Now in the case you've stated where a 520 was removed and replaced with a 550 then yes a W & B and a 337 is needed because there is a weight change.

Personally, I would do a W & B on any aircraft that goes through an engine overhaul. Airplanes tend to gain weight as time goes on, just like we do!

[Short Field]

 Almost any change in equipment requires a new W&B.  If it is just a remove and replace with the same equipment (as in a engine overhaul), then there is no requirement for a new W&B.    Most new W&Bs do not involve actually weighing the airplane.  They are paperwork exercises - i.e. radio weighting 12 lbs taken out and replace with a radio weighting 8 lbs at ARM +56". 

Like a lot of us, planes get heavier with age.  Unless you have a compelling reason, putting a plane on the scales just to drop 30 lbs of "official" useful load is not normally done.  What is safe vs what is legal is a major topic on some web sites.  The safety factor of some airplanes is truly awesome.

[starshippe]

   it was late september in '85 when i climbed into 667ga, a t41b that our squadron had been newly assigned. one decimal three hobbs hours later, she was home. as maintenance officer, i started preparing for an introductory class for the squadron, which included the new weight and balance numbers.
   as the t41b aircraft came out of service with the army, the engines were swapped out with smaller ones, by a shop in alabama, in our case. the weight and balance changes were all "paperwork exercises," strictly pencil pushing calculations.
   i couldn't help but stare at the sheets in front of me. the new weight and balance indicated that the smaller lighter engine now in the aircraft had moved the cg forward. continued staring did not seem to make any difference. how could this be?
   in looking over the calculations, it became obvious pretty quick that the error had come from the fact that the "minus" change in the engine weight had not been multiplied by the "minus" arm, which was due to the fact that the datum was behind the engine, at the firewall, and not in front of the engine. the empty cg was in error by over an inch. efforts at spreading this word were "shunned." too much trouble, i guess.
   so, if it were me, and there were any changes at all to the weight and balance, i would check them closely. even if u get the aircraft weighed, check that closely too.

bill
 

[simon]

I did some more research in the interim and as SarDragon pointed out, the answer lies in in 14 CFR Part 43. In a nutshell, "Yes".

The key part is the change from a 520 to a 550. It is a "Powerplant major alteration", as it involves "Conversion of an aircraft engine from one approved model to another". This triggers the form 337, which has to be given to the owner and the FAA.

But that's not the end of it. As I found out today, the owner then has to obtain an STC for the 550. Who has the STC for a 550 in an A-36? I don't know. I know DeShannon has one, but it might be for a certain engine variant. Beech sells the A36 new with a 550. Maybe they have it. Who knows? Does an owner have to pay for the use of the STC?

The STC for an existing, approved engine in the A36 might not be a big deal, but I realized something more significant today. A powerplant STC is a combination of a specific airframe, engine and propeller. The propeller, although overhauled during the engine overhaul, is the same one from when the 520 was in the aircraft. I wouldn't be surprised if the propeller for the 550 is a different model than with the 520. Maybe its the same? But the A36/IO-550 STC will also list a propeller model and if the owner doesn't have that same model, the STC is not valid. At least that is my understanding of an STC.

Maybe that's why the mechanic didn't want to stir up the pot. Creating an even bigger bill for the owner by having to replace the prop?

The IO-520 to IO-550 upgrade is very common in pre-1984 A36's. I wonder what others have done. Probably a question for the Bonanza Society.

[simon]

I found the STC's for an IO-520 to IO-550 upgrade in an A36. There are three. D'Shannon, Atlantic Aero and Mike Jones Aircraft Sales. Each mentions certain compatible propellers. D'Shannon doesn't even mention which propellor models. You have to contact them for details. I read elsewhere that D'Shannon charged $2500 for an STC. But then of course, each STC is going to specify certain parts, e.g. baffles etc., which have to be part of the installation to qualify for the STC. It sounds like a nightmare.

[bosshawk]

Simon: not necessarily a nightmare, but an expensive proposition.  This conversion is done all the time in Bonanzas, so it is pretty straight forward.  I, too, suspect that a differenct prop is needed, but I am not the authority on the subject.

I have a 33 Bonanza and I know of several engine conversions with STCs.  EXPENSIVE, so I have avoided it.

[Spaceman3750]

I think there's an argument to be made here for experimentals .

STC? I don't need no stinkin' STC!

[NIN]

Maybe that's why the mechanic didn't want to stir up the pot. Creating an even bigger bill for the owner by having to replace the prop?

I have to question an A&P who would do work without the required paperwork (its not like you swap engines in a plane like a shade-tree mechanic) or would want to not do some work that he potentially had to do, or should have been done (both legally and ethically) to avoid "stirring the pot."

An engine swap has an STC associated with it if its not a factory produced aircraft/powerplant combo covered under a  Type Certificate (ie. an engine/airframe combo that wasn't created in the shop/factory of the owner of the Type Certificate or Airworthiness Certificate).  Billy Bob doesn't decide to jam a PT-6 in the nose of his Cherokee Six and call it a Meridian and a day. Noooooo. The FAA wants some paperwork.

So a mechanic who will gladly take your money and hand you an airplane that is quite questionably airworthy is, IMHO, not much of a mechanic.

BTW, the FAA is really, really big on those "per-day" fines for non-compliance.

[vento]

I just did an overhaul on my engine and no new W&B or 337 was required. As far as I understood, an overhaul is usually done to the SAME engine (and in a few cases the SAME model of engine).

If an engine came out and another different one went in, then it is an alteration (337 required) and sometimes called conversion or upgrade.