Tach Time

Has anyone installed a tach time gauge in their aircraft? Can you? With hobbs time running up to 25% more than tach time it seems it would be useful for resale and engine overhaul time.

Don’t put a tach time meter - install an airswitch. We have had an airswitch installed in our SR20 since we got it (the Hobbs is stil there, useful for recording loggable time) but the airswitch records wheels-off to wheels-on time - which is precisely what the FAA defines as time-in-service. It will save you money over either tach or Hobbs time.

It’s just an hourmeter wired to a pressure switch on the pitot line.

For those with the Arnav engine monitor, you can download the data into Excel, and sort and total by time in which the RPM was over a certain level.

This is the poor man’s alternative. (After purchasing the engine monitor, you’re poor by definition.)


Derek: Gordon has a good idea in just wiring an airswitch in series with the existing Hobbs. The question is whether you can get approval to do that since the existing Hobbs is part of the type certificate.

Another option is to replace the mechanical tach with an electronic tach which also records flight time and tach time. The instrument is configured by the manufacturer with “Caution Range” “Restricted Range” “Red Line” “Safe Operating Range” which is said to be equivalent to "Normal Operating Range on the mechanical tach.

It is available at Electronics International Inc. www.Buy-EI.com.

They were kind enough to send me full literature including the Installation Manual for the RPM R-1.

The Tach Time records a running total of time the engine is above 1300 RPM. They say the time is stored for life, there are no internal batteries and that bus power is not required to keep the memory alive.

The unit sells for $475. On the order form you specify # of cylinders, “Red Line” RPM, and red “Restricted Ranges” or yellow “Caution Ranges” Tach Time (set to 0 unless specified otherwise) and any special signal inputs (other than a magnito). The existing tach cable port on the engine is sealed with a cap (available separately at $4.95).

I asked them if they had any plans to have Cirrus offer this unit as a factory option, and they said no. However, it should not be difficult to install.

In addition, there was as I recall at least one post about problems with the mechanical tach failure. This instrument is all electronic. It has a 4 digit lcd display that displays RPM, a series of led’s around the edge in a circular pattern (thus the “Red Line” “Restricted Ranges” etc.) and two buttons. One displays FLT TIME which is defined as RPM greater than 2000 for more than 10 seconds. The other button displays TACH TIME.

The FLIGHT TIME function continues to count until the RPM drops below 2000 for 10 seconds at which time the FLIGHT TIME and peak RPM are stored im memory. The last flight time and last peak RPM are stored in memory, and will be available even if power is shut off.

It would seem that there are some benefits to the instrument in addition to the TACH TIME issue on the original post. There is a greater precision in setting engine RPM with the 4 digit display. The including of all of the restriction warnings would seem to make a form 337 approval go smoothly. And, as has been pointed out, the savings in oil changes, scheduled maintenance, resale value, etc. of having a verifiable TACH TIME figure in the aircraft would save more than the cost of the instrument.

I have no financial interest in making or selling this instrument. Contact Electronics International Inc. at the url above or at 63296 Powell Butte Hwy, Bend, OR 97701 (541) 318-6060 and they will send you all of the information including the Operation and Installation Instructions for the RPM R-1.


I definitely want to do this on my SR22 when I get it. A few questions for you.

o Any reason that you didn’t put the airswitch inline with the built-in Hobbs?

o Where did you mount the new meter?

o Can you tell us the manufacturer and part number?

o Did you have to do a 337?

Thanks for the info.

Doesn’t the Garmin 430 have a flight timer integrated in it somewhere? That is, can’t it determine when the plane is moving over X knot per hour and begin a (cumulative) timer ?
I asked the Garmin rep this with an affirmative response at OSH, but don’t have my '20 yet to try it. Also, could that be loggable as the plane’s flight time?


Who did this mod for you. Do they have the mod approved? Can you email me at greg@csinet.net any info you have. I would llike to do this mod on my 22. Thanks


The ET function on the transponder does the same thing, only not cumulatively over multiple flights. I just keep a paper log (hardbound aircraft log - N.A.P.D.A. model SA-2) in the kick panel pocket on the pilot’s side (where I keep my laminated checklists as well), and write down the transponder’s ET for the flight time every flight - putting the checklists away reminds me to make the entry. Log has columns headed:


The log has 86 pages with 18 entry lines per page, plus extra pages for notes, VOR checks, etc. I figure at an average 1.5 hours per flight, its good for the TBO life of the engine at least.

Nice things about using the paper log is that it cost all of $5, it lets me add comments about the purpose of the flight or anything else noteworthy to augment my own memories later, and it satisfies the IRS’s requirements for logging time to separate out business flights from personal flights. Its not as nifty a gizmo as a separate airswitch-activated Hobbs timer, but it does the same job and has what I consider to be major advantages when it comes to record-keeping. Down side is that it takes a minute to write down the info after each flight, but it also has the bonus of being a back-up in case I forget to write down the flight in my pilot log – I can go to the plane and simply look up the date, time, conditions, etc. if I forget to make the pilot’s log entry one day…

Everyone has a system they like, and mine may be too luddite (sp?) for most folks, but it gets the job done.

o Any reason that you didn’t put the airswitch inline with the built-in Hobbs?
If it had just been up to me, that’s probably what I would have done, I don’t know why it
wasn’t done that way.
o Where did you mount the new meter?
It’s just below the existing meter, an aluminum bracket was made up to mount it.
o Can you tell us the manufacturer and part number?
Not offhand, but I can find out.
o Did you have to do a 337?

No, because we’re in Australia, so it was done under CASA rules, but it was AFAIK just signed
off by the avionics technician who installed it.

The real question is will a buyer believe any of that? I would want to see real engine time. Also, something as simple as oil changes should be done on tach time. At least this is the way I’ve read the engine manufacturer’s suggest. I don’t know what a tach time gauge costs, but it should be more than paid for through oil changes and the sale of the airplane down the road by reading up to 25% lower than your hobbs.

Does our meter record from the time engine starts or from time batery switch is on pleas advise from Don

It records the time from when the alternator is producing voltage - so that basically means while the engine is running.

That would seem to me to .What we should use for oil changes and time on airframe and engine. Its not working as hard but it is still working and wearing me for one .If I were to buy another airplane thats what I would concider for time in use. I know some rental planes start ameter when the power is on. From Don Cirrus705DM

I’ve heard that most of the engine wear occurs during the few seconds before the oil pressure rises. So that ground running time is actually most critical!


True, but that won’t account for the hundreds of hours of difference in resale value for the engine at TBO. A typical hobbs time of 2,000 may only be 1,500 engine hours as measured by a typical tach. So selling your plane then would tell the buyer it is completely runout, but in reality has another five years at 100 per year of engine life.

Much of your time is at lower RPMs such as ground time, touch and goes, pattern work etc.

All of the other methods mentioned to measure the time are good, except that I doubt a buyer would consider anything except tach time as true engine time. (They would also consider the hobbs, but that is not in the our best interest.)

I think the lack of a recording tachometer is a serious problem of Cirrus aircraft. But speaking as somewhat of a fossil, who enjoys flying fossil aircraft: there is a low-tech solution: keep a journey log, i.e. a separate logbook that records evey flight. It’s required in some countries (e.g. UK, Canada). It’s the basis for the airframe hours on my own airplane. I recently came close to buying an aircraft that had no time-recording instrument of any kind, and the journey log was the only way to know how much time was on it or the engine. It was meticulously kept over a 45-year period, and it convinced me that the hours logged were accurate. Just as with maintenance logs, the care with which they’re kept says the most about the quality of an aircraft that’s offered for sale. This works best when the sole owner is the sole pilot, or in small partnerships. In any case, a journey log is a very good idea and a very satisfying thing to do. I keep track of fuelings and oil changes in mine, so I have a good idea what my engine is up to. Try it, you’ll like it! and you’ll be able to tell your buyer, some day years from now, what the real time is.


>Try it, you’ll like it! and you’ll be able to tell your buyer, some day years from now, what the real time is.


Thanks. For a long time now, I’ve been keeping a log of every flight; I jokingly tell my passengers that I keep track of useless information just to satisfy some compulsive urge. You just made me feel good, because I realize that I can indeed calculate the EXACT in-flight hours on my airplane; and bad, because it’s going to be quite a job to go through all those little “books”, 10 trip-logs each, and add up the hours and minutes.

Do you have any creative ideas for what I can use 355 hours worth of…

… exact times of fuel tanks switchovers;
… exact times, names, and frequencies of ATC handoffs
… exact times and values of altimeter settings received
… etc…?

It doesn’t matter… we compulsive types HAVE to write this stuff down… because… well, there are these little boxes to fill in on the flight-log-form. Who put them there? Well, I did… because… well, you never know! [;)]

  • Mike.

Do you have any creative ideas for what I can use 355 hours worth of…

… exact times of fuel tanks switchovers;
… exact times, names, and frequencies of ATC handoffs
… exact times and values of altimeter settings received
… etc…?

My girlfriend thinks I am anal. I can’t wait to tell her about you.

Greg, the mod was done here in Australia, and was simply signed off by the appropriate maintenance person. I would expect the same would apply in the US, since it doesn’t appear to constitute a “major alteration” as defined in Appendix A of FAR part 43 (major alterations require a form 337). Ask your local maintenance shop.


Sounds like a fine system - we keep something similar. How non-volatile is the transponder memory? In our case, a new transponder would have been much more expensive than having the airswitch fitted anyway.