Correct method to log time Hobbs or Tech
 

What is the correct source for logbook time entries, the hobbs or tach or chocks off to chocks on? During training and renting aircraft after getting my license my time was always taken from the Hobbs (In the US). Now I am flying my own aircraft I was wondering which is the preferred method from an insurance company viewpoint.

Your logged time as the pilot flying the plane should be the same as the time the plane's flying (flight) time. Therefore I do, and suggest to you, that you use the time of day wheels off, to wheels on as your "air time". It seems customary to add 0.2 hours to that, so as to determine "flight time" for the aircraft (taxiing etc.). Hoobs and tach time are not really that accurate, and I would not want to depend upon them. I have certainly known Hobbs to not work, and tachs be quite in error.

I have never known this "air time + 0.2 hours" formula to not be accepted for logging piloting time, though others may do it differently.

Those decimals of an hour won't seem so important to you later in your flying career...

In UK it's brakes off to on. You're Pi/c from the moment you start to taxi. Yes, I know you're Pi/c when you sign the tech log but let's not get too pedantic.

Having said that I wouldn't log any time for taxiing to the hold, finding a fault and taxiing back in.

Which logbook are you talking about? If it is the pilot's logbook, you record the time from brakes off to brakes on (it is acceptable to use take off to landing plus 10 minutes). If it is the aircraft/engine logbook, it is acceptable (to the CAA and LAA) to log the time from take off to landing. The Hobbs or tacho are usually only used for working out the cost.

Good point, as Piper says, tech log time is flight time. Our tech logs have a column for both brakes off/brakes on and flight time. It's the flight time you deduct from the total for time to next servicing.

I see the OP is in the USA.

AFAIK pilot time is logged brakes off to brakes on, and aircraft time (for maintenance purposes) is logged as airborne time. It's in the FARs somewhere...

Same on G-reg.

For practical purposes, a lot of people log hobbs time etc, but that is because it is easy to read off and cannot be tampered with by persons unknown.

I concur with the previous posts - pilot logbook is brakes to brakes, whereas aircraft logbook is airborne to touchdown.

Despite the earlier comment, the regulations clearly state that you should log brakes off to brakes on when you "intend" to go flying. Thus, taxying to the fuel pumps is not loggable, but if you taxy to the hold, find a fault, and taxy all the way back, that can quite clearly be logged since you were planning on flying.

When you get to more complex aircraft, it doesn't even feel like cheating to log all that time. In a multi-engine antique piston aircraft type conversion course, by the time you've made it to the hold-short line, the lesson is pretty much finished!

And a final point - if you want cheap hours building, find an airplane where rental charge is for airborne time only, and fly it to a HUGE airport, land, and taxi to the ramp. You'll easily put 20 minutes taxy in, then 20 minutes taxi back out, in the logbook. :E

No suprise you live in Scotland :E

In the UK you can only log time that includes actually flying. Taxiing with the intention to fly and then parking again can't be logged. I've been through this with the CAA before.

The requirement that was formerly contained in the UK ANO can now be found in EASA Part FCL Regulation 1178/2011. The UK ANO Article 79 continues to include the regulation regarding helicopters. EASA Part FCL:
Clearly if you don't fly, there is no flight time, but taxi time before and after flight does count.

So if i am reading the replies right, the correct method is a manual log of time from brakes off to brakes on that involved an actual flight ( not taxiing out and have a change of mind) which makes sense, and forget about both the hobbs and tach.

The reason I ask is I am not really that interested nor care about "hour building" as i am a recreational flyer and will remain so. However I do want stay within accepted norms for hour logging for insurance purposes, as each year when the policy comes up and they ask me how many hours I have, I want to be accurate as I can just imagine what loopholes they would use if there was a claim.

True. But for all practical purposes, how much time is there between engine start and brakes off, and how much time between brakes on and engine off? If it's more than a minute in total you might want to take a careful look at your checklist and ask yourself why you are burning all that expensive avgas, without using it for airframe propulsion somehow.

Generally it's less than a minute. Maybe two if you're really slow. Since you're rounding to the nearest five or six minutes (depending on the way you log: minutes vs. decimal hours) that time is rounded away anyway.

So if your aircraft has a hobbs meter, and the hobbs meter is wired to engine on/engine off, you might as well use that as your basis to log flight time. (But note that a hobbs can be wired to anything. At our club we've got a few aircraft that have a hobbs wired into the pitot/static system, and they only log time when the aircraft is doing 30+ knots, i.e. flight time.)

Especially in winter, the engine spends quite some time running the oil up to the recommended minimum of 50 deg C. I assume this running time should be taken into account for determining engine maintenance intervals.

I do not keep a separate engine running log, so I use the aircraft log for maintenance intervals, and that one mentions Hobbs time and my Hobbs timer is currently wired to run as long as the master keyswitch is "on". I plan to wire it through an oil pressure switch, though.

Or would the o/p really mean a separate "technical log" to keep track of the engine's running, separate from the aircraft's log?

So that my aircraft log does mention Hobbs time. And during my tuition, I was told that all logs (aircraft, pilot, airfield) must mention the same time for beginning and end of the flight. But that was outside CAA-land.

There are a number of methods that are generally acceptable:

Hobbs time
Brakes off to Brakes on
Tacho plus a factor, usually 0.1
Airborne time plus 10 minutes or 0.2

If you are flying at a school they are generally interested in charging the most, hence the Hobbs. The Tacho is used for engine running time, but can read low if the rpm is low, and may be 0.1 low at the end of a PFL lesson. If its your aircraft the choice is yours.

An excellent reason for taxiing slowly!

And one last question regarding time. Can someone please explain how the tach differs from the hobbs by a factor of 1.1 to 1.2, I understand that the hobbs is off the master and the tach is off oil pressure (which would give a very slight time difference when starting and shutting down) but am I correct in saying the engine has to be above a certain rpm or producing a certain HP for the tach to engage and start counting, if so is the tach so sensitive it can detect the oil pressure difference between an engine taxiing/idling at 1000-1200 rpm and economy cruise at 2300 rpm,

Also does the tach not count/run below a certain rpm threshold or does it count/run at a slower rate until it hits a certain rpm or oil pressure that then triggers it to count the hours at the same rate as the hobbs does ?

I log Hobbs time. From the time the engines run, as far as I'm concerned, that's flying. Taxiing is flying, run up is flying, etc, etc. Anytime the aircraft moves under own power, it's flying.

Nope. The tacho simply runs off the RPM. It's integrated in the RPM instrument after all.

All tachos are calibrated to a number, typically somewhere in the 2350-2500 RPM range. At that calibrated number, the tacho runs "true", so 1.0 tacho hour equals 1.0 wall clock hours. (The number might be stamped on the instrument, but typically on the side or on the back, where it's not normally visible.)

Rev the engine at anything higher than the calibrated RPM and the tacho runs faster. Anything lower and the tacho runs lower. So if you're doing aerobatics, running the engine at its highest RPM setting all the time, you may easily clock up 1.2 or 1.3 tacho hours in one clock hour. But in contrast, in a slow cruise you may only run up 0.8 tacho hours in one clock hour. And even when idling the tacho runs. Although it will only show around 0.2 or 0.3 per clock hour.

Since the tacho time is much better related to engine wear and fuel/oil consumption compared to hobbs time, tacho time is used in a lot of places to calculate the aircraft rental fee.

Comparing hobbs (regardless of how it's wired) to tacho time may also flag abnormal behaviour by renters. For instance, if each one-hour bimble normally shows 0.8 tacho hours for each 1.0 of hobbs hours, and all of a sudden you find someone who had 1.1 tacho hours for 1.0 hobbs hours, you know you've got to ask some questions. Because they may be abusing the aircraft.

There are different kinds of hobbs meters.

Some just count engine revolutions, and are calibrated to read hours assuming say 2300rpm. I think most GA types are in that category.

Some read time but only if the oil pressure is over X psi.

Some read time but only if the rpm is over say 1200 (mine does that).

Some are purely electric, and people have been known to turn off the master switch during flight to reduce their bills :)

My club is very strict "time from startup to shut down" and "hobbs"

Im not sure what the hobbs meter is wired too but if its not going to register until i start take of run then i may just forget to write my times down every now and then ;)