In reply to:
Hi: I was just told by a A/P that in order to install a new tach in our planes that it would have to be FAA certified for Cirrus or STS and that it could not be used to log engine time to TBO. Does anyone know if this is fact? The savings in dollars is just to great not to have one installed, if it can be used as “official engine time”. I still have a very low time engine and every minute counts.
A couple of points here, and also a couple of opinions:
Under part 91, if not operated for hire, there’s no requirement to overhaul the engine at TBO. So, I’m not sure what you mean when you ask “can be used to log engine time to TBO”, since reaching TBO doesn’t really have any meaning, except perhaps in the marketplace when you’re trying to sell a plane with XXX hours, and TBO is YYY.
It seems that each regional FSDO has slightly different rules about these things, in terms of paperwork required for installation. Bill Dobson has mentioned this w.r.t. getting GPSS installed (for example, I personally did not seem to require a 337 for installation, just a log book entry - others are the same. But the FSDO near Bill wants a 337 or STC).
Personally, I would think that it wouldn’t be TOO hard for a shop to write up a 337 (major alteration form) for installing a tach, as long as the tach is certified [STC’ed] for use in SOME certified plane, not necessarily a Cirrus. It will be some extra paperwork – and thus some extra money on your part – but doesn’t seem to me to be too bad. But then again, if your FSDO is a real stickler for things, maybe this route isn’t open to you.
- Personally, I do not really see the value of having a tach installed in the plane – and I do realize that this runs contrary to most of the opinion within this group. It seems to me that if I want to save money by delaying oil changes, etc. by 20%, then I should just do that, regardless of having an extra tach. In other words, I could just change the oil every 60 hobbs hours (= 50 x 1.20) rather than every 50 hobbs hours. I choose not to do this personally, and instead choose to change my oil every 50 hobbs hours, but I could see why someone would want to do this.
Similarly, you could delay other maintenance; if you wanted to change your vacuum pump every 500 hours, just change it at 600 hobbs hours (= 500 x 1.20) instead.
Others have proposed that reselling the plane will be easier because you can say “it only has XXX hours” (rather than XXX x 1.2 hours as recorded on the Hobbs).
But if I were buying a used Cirrus, I would compare apples to apples. Since EVERY Cirrus has a hobbs meter, I would ask you what the hobbs time was, so that I could compare it to other Cirruses I was shopping for that did not have a tach. So I’m not even sure it buys you anything there, either.
In summary, given that non-hire part 91 does not mandate overhauls at a certain time, or oil changes at a certain time***, etc. it seems to me that there’s not a whole lot of rationale to installing a tach meter.
But that’s just me - I understand that others feel differently.
*** the only exception I can think of is that some ADs require compliance within a certain # of flight hours. But that doesn’t seem to be THAT big a deal. And of course, if you’re renting our your Cirrus, or otherwise using it for hire, then most of my argument is moot.