Aircraft total time calculation reference?

[SkepticalJohn]

I understand Tach time and I understand Hobbs. Can someone explain Total time AND give a reference please?

 

I've seen / heard opinions claiming 1.0 tach = 1.0 Total. I've seen the same for Hobbs and I've also heard wheels up to wheels down.

 

Thanks in advance,

John

[carusoam]

TT is total time of the aircraft has been operated.  Often the rules for a pilot logging flight time will vary from what the engine gauges are measuring.

TTSMOH total time since major overhaul.  Is a hint to how many hours are left for the next owner to use.

 

If you are buying a plane, the old mechanical tach has a continuous counter on it.  The count is presented in units of time.

realisticaly, it is not a perfect number of hours that the plane actually flew, but a pretty close approximation.  There is a particular rpm for the gauge that equals an exact hour.  The exact rpm gets printed on the meter's case.

When determining how worn out the engine is, the Hobbs meter does an adequate job.  

Realistically (part 2) when an engine is well cared for the hours keep increasing and flight beyond TBO can occur.

when an engine is run hard, that won't show up on the Hobbs meter either, but the engine or its cylinders may not make it to TBO...

 

When following the maintenance manual, it will make references to engine hours.  The mechanic will use the device supplied by the plane itself.  Whether it is flight time or Hobbs hours...  the maintence matches the procedure with the tools....

 

How does that sound?  What are you trying to determine?

PP thoughts only, not a mechanic...

Best regards,

-a-

Edited February 23, 2017 by carusoam

[jlunseth]

Well, total time as you see it in ads for aircraft has more to do with how many engines the aircraft has had, and it is really an airframe time.  Run engine one to TBO at 1800, put in a new engine and run that one to 1800 and now you have 3600 TT, but having just put your third engine in, you have zero engine hours whether you measure by Hobbs or tach.  Some aircraft have TT airframe limits, the airframe is supposed to be overhauled at 10,000 TT, for example.  I only have a Hobbs in my aircraft, that is what I go by to maintain the engine.  After the first engine (different owner), a reman was put in (zero engine hours) and not long after that, according to the logs, (about 64 hours later) a new Hobbs was required, so my TT is the life of the first engine (I think it was 1800) plus the 64 on the new engine, plus whatever is on the meter now, somewhere around 1700,for a TT of 3564.

 

 

 

 

[kortopates]

4 minutes ago, SkepticalJohn said:

 

I understand Tach time and I understand Hobbs. Can someone explain Total time AND give a reference please?

 

I've seen / heard opinions claiming 1.0 tach = 1.0 Total. I've seen the same for Hobbs and I've also heard wheels up to wheels down.

 

Thanks in advance,

John

 

The FAA does not recognize the term Total Time so I assume asking about Time in Service for maintenance purposes. Such as in the perspective of the Mooney Hour Meter discussed in the another thread.

See FAR 1.1 definitions,  

Time in service, with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.

Although more expensive aircraft actually have meters that read time in service per the definition above, Tach time is the most common proxy for measuring it. But of course its not truly 1:1 with time you would more accurately measure per the definition with the proper device. But for purposes of recording time in service its very common method. But we're actually counting more than the time intended with a simpler device. But wheels up to wheels down is all that we would actually want to record. Idling and taxing don't count. 

[SkepticalJohn]

The FAA does not recognize the term Total Time so I assume asking about Time in Service for maintenance purposes. Such as in the perspective of the Mooney Hour Meter discussed in the another thread.
See FAR 1.1 definitions,  
Time in service, with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.
Although more expensive aircraft actually have meters that read time in service per the definition above, Tach time is the most common proxy for measuring it. But of course its not truly 1:1 with time you would more accurately measure per the definition with the proper device. But for purposes of recording time in service its very common method. But we're actually counting more than the time intended with a simpler device. But wheels up to wheels down is all that we would actually want to record. Idling and taxing don't count. 

Thanks for the fast replies!

The aircraft I fly for a profession spits out the numbers and I write them down - my K, not so much...

I was logging an oil change in my engine log. The aircraft has a Hobbs and tach. The gentleman who had it before me has always recorded tach, Hobbs, and total for all of the entries. I was trying to figure out what to put in the book for Total. Some entries he'd entered before were reflecting a change in Hobbs, other entries married up with tach, others agreed with neither.

I'll have Total follow along with the Tach from now on.

Thanks again gents!

[1964-M20E]

I would choose on or the other and go on and not worry about it.  For me it would be the Tach and base any time related maintenance on it.  Planes have some sort of tach in them that records approximations of time not all planes have a Hobbs meter. 

In helicopters some the Hobbs is connected to an oil pressure switch and others to the collective so it varies.

 

 

[goterminal120]

Rule of thumb is tach time is for maintenance, hobbs time is for renters.

[Sean S]

AFAIK every aircraft has a tach. Not every aircraft has a hobbs. Go with tach time for maintenance.

[amillet]

97 J has only Hobbs. No tach

[Sean S]

...and I did not know!

[carusoam]

94 O has no hour meter on the tach.  It has a tach.  Without one it would be hard to set the power properly...

I think Alan may have left out that part... 

Best regards,

-a-

[kortopates]

1 hour ago, amillet said:

97 J has only Hobbs. No tach

I assume your calling it a "hobbs" meter because its an independently mounted meter just like a Hobbs meter. If its mentioned in your POH, you'll find "Hour Meter", and if so it likely only simply says that it reads elapsed time the engine is running. Which is only partially true. If you pull out the service manual schematic I'll bet you'll find its wired off your electrical tachometer, regardless of where your Hour meter is (baggage area or on the right of the center console).

But perhaps you have already compared its tracking of engine time over flights and found it reads about on average 0.2 less that actual elapsed time of the engine running, which would confirm its electrically running off your tachometer? 

[Guest]

In Canada we record our flights in a journey log book which forms part of the technical records for the aircraft.  We record start to stop time for your pilot log and record time up to time down for aircraft total time.  

Clarence

[Bob_Belville]

I suspect my plane is or will be more common in that I have a JPI 930 and it's memory is the only place that "tach" and "Hobbs" time are accumulated.

[Marauder]

23 minutes ago, Bob_Belville said:

I suspect my plane is or will be more common in that I have a JPI 930 and it's memory is the only place that "tach" and "Hobbs" time are accumulated.

Bob - I thought they were required to put the tach time at the "total time in service" number. Where did the 917.7 come from?

[Bob_Belville]

5 minutes ago, Marauder said:

Bob - I thought they were required to put the tach time at the "total time in service" number. Where did the 917.7 come from?

Chris, I believe the installing shop set the tach to the old tach which was zeroed at the factory reman engine installation 2001. The 2 values do not increase in tandem. The "Hobbs" is 939.6 higher than it was at the engine change.  

[Marauder]

1 hour ago, Bob_Belville said:

Chris, I believe the installing shop set the tach to the old tach which was zeroed at the factory reman engine installation 2001. The 2 values do not increase in tandem. The "Hobbs" is 939.6 higher than it was at the engine change.  

I had a similar situation but mine was related to a replacement tach that was installed, The plane had over twice the amount of time the mechanical tach was showing and there was always a logbook calculation done to reveal the true in service time. This was further complicated when that mechanical tach was replaced with an EI unit and then the JPI 900 was added. When the mechanical tach was replaced with the EI, it was set to match the true "time in service" value. TSMOH for the engine was calculated in the logs from that value. When I added the JPI, the "time in service" value was set to match the EI. After a year of watching them total up time, the JPI is running faster than the EI. It may be related to the threshold of when each of these units begin counting. 

[ArtVandelay]

I suspect my plane is or will be more common in that I have a JPI 930 and it's memory is the only place that "tach" and "Hobbs" time are accumulated.

You need to clean your JPI screen, your fingerprints are all over it. Especially if taking photos

[Yetti]

Tachs come and go.  Hobbs come and go.   Total time is the summation of all those comings and goings of the recording devices.

[kortopates]

4 hours ago, Yetti said:

Tachs come and go.  Hobbs come and go.   Total time is the summation of all those comings and goings of the recording devices.

Good point and in truth its even more complicated than that since with every annual inspection we need to report both Total Time in Service as well as Total Time in Service Since Major Overhaul. For most of us flying an older aircraft, the aircraft hour meter will only be good for air frame total time in service and we'll be doing arithmetic for both engine times. (Add in consideration for the prop as yet another life limited appliance we need to track total time in service independently) 

8 hours ago, Bob_Belville said:

I suspect my plane is or will be more common in that I have a JPI 930 and it's memory is the only place that "tach" and "Hobbs" time are accumulated.

Bob is very correct, plus these modern engine analyzers give us much more flexibility. I can't say for all of them, but I really appreciate how the EDM-9xx series does this for us. It gives the means to accumulate airframe time separately from engine tach time and it will also tell us the individual flight time. What is nice about the EDM-9xx series is that provides an excellent alternative for tracking engine maintenance time in service since doesn't begin to record tach time under 1000 rpm and then it uses a programmable set "Average Crusie RPM", with a default of 2400 rpm, which is what RPM is used to record 1:1 tach time.  For most favorable tracking, you could use a setting of 100% of redline, but traditionally these have been ~2456rpm in the OEM Mooney hour meter.

Edited February 24, 2017 by kortopates

[Bob_Belville]

1 hour ago, kortopates said:

Good point and in truth its even more complicated than that since with every annual inspection we need to report both Total Time in Service as well as Total Time in Service Since Major Overhaul. For most of us flying an older aircraft, the aircraft hour meter will only be good for air frame total time in service and we'll be doing arithmetic for both engine times. (Add in consideration for the prop as yet another life limited appliance we need to track total time in service independently) 

Bob is very correct, plus these modern engine analyzers give us much more flexibility. I can't say for all of them, but I really appreciate how the EDM-9xx series does this for us. It gives the means to accumulate airframe time separately from engine tach time and it will also tell us the individual flight time. What is nice about the EDM-9xx series is that provides an excellent alternative for tracking engine maintenance time in service since doesn't begin to record tach time under 1000 rpm and then it uses a programmable set "Average Crusie RPM", with a default of 2400 rpm, which is what RPM is used to record 1:1 tach time.  For most favorable tracking, you could use a setting of 100% of redline, but traditionally these have been ~2456rpm in the OEM Mooney hour meter.

Paul, can my 930 be programmed to display the flight times? By me or my A&P?

[kortopates]

18 minutes ago, Bob_Belville said:

Paul, can my 930 be programmed to display the flight times? By me or my A&P?

If you are asking about how to get to that screen, Holding the LF and DIM button together should display the screen I showed. Its shown on the 9xx series Pilot Guide on page 22. 

[Bob_Belville]

52 minutes ago, kortopates said:

If you are asking about how to get to that screen, Holding the LF and DIM button together should display the screen I showed. Its shown on the 9xx series Pilot Guide on page 22. 

I press the middle 2 buttons to get the screen I posted above. I'm asking how that screen gets formatted to show the extra info. I'll check my PG.

[kortopates]

4 minutes ago, Bob_Belville said:

I press the middle 2 buttons to get the screen I posted above. I'm asking how that screen gets formatted to show the extra info. I'll check my PG.

I am not sure why but my guess would be it may not display til the airframe time has not been set in Program Mode. All of these are non-primary and settable from Program Mode. These parameters are on page 45 of the PG. Perhaps if you review them in Program mode and set if needed they will then display. I have not yet seen anything yet that enables/disables them.  

[Bob_Belville]

Just now, kortopates said:

I am not sure why but my guess would be it may not display til the airframe time has not been set in Program Mode. All of these are non-primary and settable from Program Mode. These parameters are on page 45 of the PG. Perhaps if you review them in Program mode and set if needed they will then display. I have not yet seen anything yet that enables/disables them.  

Thanks, I'll look around.