You really don't need a new flight manual. The FAA allows HP increases of less than 10% to be Field Approved. The 337 would list the engine substitution, and that the performance is equal to or better than the original, and the flight control limits have been adjusted to the 160 HP specs.

There is no gross weight increase, no stall speed change, the only mechanical change is to the up/down elevator stop adjustments, and the left/right rudder stop adjustment.

That's it.

Sounds great but you still have to talk an ASI at the FSDO into approving the field approval.

Sadly that might not be possible.

You really don't need a new flight manual. The FAA allows HP increases of less than 10% to be Field Approved. The 337 would list the engine substitution, and that the performance is equal to or better than the original, and the flight control limits have been adjusted to the 160 HP specs.

There is no gross weight increase, no stall speed change, the only mechanical change is to the up/down elevator stop adjustments, and the left/right rudder stop adjustment.

That's it.

That's it.[/quote]
Hi Glenn, I am aware of the 10% power increase job aid, my DER approached the FSDO with that when preparing the field approval. The ASI at the FSDO said that they want a Manual Supplement written, and of course that had to go to the ACO. Do you have an example of a previously approved 337 for a similar alteration?[/quote]

I will look up the flight manual supplement for a similar PA23. It is the one where an Apache 235 (equal to an A model Aztec) is fitted with the higher compression pistons to make 250 HP. The FMS is next to nothing, the main change is that the fuel placards are changed from 80 octane, to 91 octane. It's the same situation as the 150 to 160 Apache upgrade. You get better performance, without any changes to airspeeds, or gross weight.

Thank you so much. The whole thing is in process but I’d like to see one regardless maybe it could be some help. Last week there was finally a response from the ACO, they wanted to know what props were being used on the installation. I of course provided the stc paperwork for the compact hub props installed……the nonsense continues

Here are the files.

This STC can be accomplished by changing the pistons alone, or by changing the engine from the O-540-B to the O-540-A. Either way, you end up in the same place.

The FMS shows engine instrument markings, and propellers, both of which are the SAME with either engine. So the only actual change, is the fuel placards. Changing from 80 octane with the B engine, to 91 octane with the A series engine.

The change from 150 to 160 would be exactly the same.

They are way overthinking this. This is something that Piper already did. The offered the exact same airframe with 150 or 160 HP. They offered it with 3500 or 3800 gross weight too, with either the 150 or 160 HP engines. All you are doing is something that the factory ALREADY DID, 60 years ago.

2000nm of Aztec flying over spring break. Only thing that would beat my NA model is a turbo and only thing I’d take over turbo would have to burn Jet A.

But the airframes are not the same inside. There are differences between airplanes below 23-1068 and later and also 23-1871 to 23-2046. Plus other odd S/N mixed in. Earliest S/N range is not eligible for the 3800 gross. The TCDS lists the ranges. Plus parts book has some other info.

The fuselage truss changes, Gear changes, VA speed changes, Flap and gear speed changes.
Internally the windshield attach is different. Piper never did allow a 160hp on the earlier airplanes in the TCDS. Would it work. Sure but it makes it tougher to say they are all the same for field approval paperwork instead of having an STC to use. Though the Geronimo went higher HP than 160 so obviously it would be fine.

The TCDS has a note saying the 235 is the same airframe as the 250hp airplane except for power plants. See section IV of the TCDS. That would be a huge help if the 150-160 had the same.

What is the Report Number for the AFM of a C-model Aztec (SN 27-2572) and where would I get a copy?

George

Totally understandable, however there have been field approvals performed to upgrade the engines on the early airplanes, those S/Ns which fell under the 150 to those engines listed on the lines of the TCDS for the 160. My plane specifically has the nacelle fairings appropriately installed as well as the VMc changes that result in that installation documented. I am sure there are other small changes with superseding parts for newer airplanes but…. It has all been submitted 6 months ago. Problem is the slowness of the ACO. Although some movement has been seen as they’ve recently asked about what propeller installation will be used (compact hub props via STC)

In short I wish there was an STC, but there isn’t, and if this doesn’t work, I will sadly have to part out this very clean preserved airplane, or figure out a way to “downgrade” the engines

Vald reconsider this. It seems to be used almost as a threat in every area of the internet these days. "I have a XXX vintage airplane with this problem so I guess I have to Part it out".
Everything from a bad cam to needing fabric. Sometimes even for less reasons.

It's a flying complete "preserved airplane airplane". If no other option just remove the cylinders, change pistons and carb. Lycoming has a procedure in the service letters to change between models. A O-320 narrow deck engine with cylinder base plates and 150hp is allowed. The performance difference is not that much with the lighter airframe performing well on 150hp. Definitely not worth KILLING a good airplane over it.

Parting out is a horrible process. You sell the engines and props. A few small things go and if landing gear sells the carcass sits for years until finally scrapped because the value of the parts left is so low it's not worth shipping or answering the phone.
There are enough damaged or corroded Apaches to fill this role.

Better off just sell the complete airplane to someone who will fix it in that case.

Is the hangup at the ACO that you have two different suffix model engines? How do you handle the difference in propeller bolt sizes? on the B2A?

Can you change crank flange prop bolt inserts to convert match both engines as O-320 B3B and have less headaches. Your B2A is not on the TCDS for the Apache.

Luckily it's the same Prop STC for 150 - 160hp and that will help for sure. That is a good sign you might be getting somewhere.

Charlie, I agree completely with your assessment and I am trying everything I can to avoid that burden as I really love the airplane and my intent is to keep it flying and upgrade it continuously to make it viable and preserved.

Re-reading my posts I made an error, I have a B1A not a B2A which is on the TCDS.

I do not think there are any hang ups at the ACO at all on a technical level, the basis of the field approval performed was the job aid as it relates to the power increase of less than 10%. The concurrence with the ACO requested was based on the AFM supplement. Supplements can only be approved by the ACO. My problem is the ACO has just not moved on anything with a bunch of rumored excuses such as holidays, DOGE, etc etc. I of course am reaching out for help and information based on other peoples experiences with similar modifications.

Of course in the worst case scenario I will be downgrading the engine to the 150 variants with the parts changes.

O-320 engine models:

O-320 Models Characteristics
O-320 Basic model - four cylinder, horizontally opposed air cooled, direct drive with
automotive type generator and starter, provides for single acting controllable pitch
propeller.
O-320-A1A Same as O-320, model designation change only.
O-320-B1A Same as O-320-A1A except for compression ratio, fuel grade and rating.
O-320-A1B, -B1B Same as O-320-A1A and -B1A respectively except have straight bore carburetor riser.
O-320-A2A, -A2B,
and -B2A, -B2B
Same as O-320-A1A, -A1B, -B1A and B1B respectively except have no provisions for
controllable pitch propellers.

Please summarize your issue. I must be missing something. Do you have one 150 and one 160HP model. If so, I have a nice low time 160 B1A available and will take a 150 in trade.

No I have a PA23-150 with 2 O-320 160 engines that I am in the process of making legal