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Discussion in 'Maintenance Bay' started by Arnold, Sep 3, 2021.
Well just for giggles, what would YOU say if you were my mechanic?
Well this one is TSO and under $1k...
When given a choice of which instrument to smash in an emergency, most students pick the hobbs meter.
TSO isn't required here, but make sure that cheap one is otherwise a legal aircraft part. A lot of what ASS sells is for experimental only.
Doesn’t matter what anyone says, only matters what the person making the log book entry (A&P) wants.
Ha. Okay, what is the specific aircraft model and S/N? What is the P/N of the existing indicator and the P/N of the intended indicator (a link would be better)?
Probably not as fast as swapping in a new gauge, but AQI will overhaul that one for $195.
Aircraft is Bellanca 8KCAB, S/N 437-78
Neither parts manual nor AFM equipment list provides a part number for the manifold pressure gauge.
However, here is a picture of the part. Gotta laugh when I look at the tag. I thought the part was original. Looks like it was installed last year, about a month before I bought it!
Prospective replacement part would be something like UMA Mechanical MP Gauge, Aircraft Spruce Part# 10-00080, MFR Model# 7-300-35.
I'm not trying to get free maintenance advice (well, maybe a little). Am more trying to understand the decision process. This thread and others on POA are full of arguments that meeting TSO is only required for a few specified items in Part 91, and everything else is up to discretion of the installer. But nobody can seem to explain how the installer goes about making that determination.
Without seeing the actual manual I can only give you a general answer. Its possible if you read the front matter of the parts manual it will explain the route to take if no P/N is called out. That said, no specified P/N can usually means one of two things, the item is a standard spec'd part (same for the ammeter) like AN, etc., or there were additional options that required different indicators depending on which option was selected. What specific engine is installed? And is it a OEM option or was it installed by STC? If it is an STC engine it could require a different track.
It's as simple as what the installer, i.e., mechanic, determines is airworthy. Even if the indicator were TSO I as the installer would still have to make the same determination as a non-TSO indicator because a TSO does not provide an installation approval. And the regulatory requirements for a minor alteration do not require the parts used in that alteration need a separate approval as my signature provides the installation approval. This is the main difference between replacement part requirements and requirements for individuals who want to produce parts for installation on TC aircraft. If that makes any more sense to you.
In that case, spend the $195 to get your existing indicator repaired and your $116 ahead.
Engine is AEIO-360-H1A. OEM option.
Front of the parts manual is below. Other than that, there is nothing except the drawing and list previously provided.
Based on what you posted, nothing stands out that would prevent installing the UMA gauge as an alteration. If you're curious you could call American Champion and see what P/N gauge was originally installed. Regardless, it falls to your APIA what they will accept. But I see no issue.
Thanks. Turns out my A&P had a spare, so I'm good.
But my real purpose is to try and understand the process better. So what kinds of things might "stand out" to prevent installing a non-TSO gauge in a situation like that? If the parts manual or AFM had a specific part number, would I have to do more research to confirm the prospective replacement part met the specs?
In general, stand out items would be if an item was part of a separate certification process like a STC or field approval which could require an addendum to that approval vs a standalone alteration. Or if the original indicator was part of a system and performed a specific system function a different indicator was not capable of. Also if it was a VFR vs IFR issue may come into play as well as any specific FAR requirements for the indicator. It really boils down to the specific part in the specific aircraft that has to be reviewed and looked at. As to having the original P/N, it definitely makes things easier all around in making that determination.
Thanks, that is actually quite helpful. Seems the internet is divided into 2 camps, like most things these days. One camp says TSO is not required and you can put whatever you want in a Part 91 aircraft. The other camp says nope, never, nothing but certified parts in certified aircraft. Makes sense that the actual truth is in between, and involves application of judgement and knowledge.
It's not a binary situation.
Agreed, but the result is boolean.
All the world's an analog stage and the digital players only play bit parts.
But most importantly to be taught. No where are mechanics taught, or required to know about, how the big picture works for maintenance regulations when they get their A&P or IA. Same with pilots who are not taught, or required to know, the regulatory ins and outs of owning an aircraft and their responsibilities. I've always been a proponent that part the required knowledge of each certificate should be how the FAR system works. Instead the only requirement is how to fly and how to turn wrenches. So its not so much the actual truth lays in the middle as it is the lack of real time knowledge how the FAR system works. The best part is that 90% of that system is there in black and white for anyone to learn to include you if you so choose.
Amen, bell206. When I took ground school years ago, I was shocked at what was being taught. Just enough to pass the exam, and nothing about owning an aircraft and what is involved.
Here is the cliff note version we were given in FAA DER training for required equipment:
TSO simply means the product was demonstrated to meet that TSO requirements without any specific installation approval to any aircraft. Typically, the TSO manufacturer gets an STC for specific TC aircraft model if mass produced, which obviously makes it legal to install on listed specific aircraft models. Without a STC or being listed on TC documents, technically you would need to reference the aircraft certification basis to see if it mentions any specific TSO requirements for that component….. more work than most will do. If it does mention a specific TSO and you have part with same TSO, it would be easy for tech to justify installation if he/she feels comfy doing so. PMA may also help the justification as well as prior field approvals that were not kicked back. This is a bit simplistic as there are other considerations, such as, say you are swapping an airspeed indicator with one from another model aircraft which has same TSO label, but the replacement is marked with different stall speeds (a TSO won’t be that specific), the tech would not likely approve it.
however, the TC holder can use non-TSO’d stuff if it is part of the TC. Such required stuff may be listed on the TCDS or equipment list. This is mostly with older certification basis aircraft as newer equipment is marketed to many different applications both OEM and upgrade and approved for different models you resourceful manufacturer. . So again, obviously TC part numbers would work for legal replacement. These part numbers may not be legal on other models or vintage of the same TC.
but at end of day the tech installing required parts without the above mentioned pedigree bears the responsibility of officially making an installation “legal”.
One more thing, don’t expect manufacturer on an experimental component to give anything in writing stating it meets same TSO as their certified model. Experimentals often argue they can use non cert IFR equipment, but regs say IFR equipment must meet specific TSO’s……here’s the rub, it doesn’t say they have to actually have the TSO paperwork, just that they meet the TSO requirement. So guys were installing experimental versions that had identical certified versions….. but to be technically legal they would need to show the part indeed met the TSO….tough to do without the manufacturers paperwork, and a lot cheaper to just buy the certified version, but most doubt it would ever be an issue.
This is the main point of the topic. Its the APIA who makes the determination and not the vender. But that same APIA requirement is applicable to TSO products as well given a straight TSO does not provide an installation approval like a PMA or STC does. So unless the TSO item is the same P/N as the original then the APIA assumes the same resonsibility as the non-TSO item.
While there is not a regulatory definition of "experimental parts" its my experience if a vendor states their article meets a TSO they will provide a letter stating so (except for certain avionics venders that is). Unfortunately as equipment becomes more digitized and complex the pool of non-TSO offerings becomes less and less especially in the avionics market.