Show of hands - Logging Engine Hours ??
 

Evening All....

What is the Correct way of Logging Engine time ?
(Can anyone point me to the CAA Rules regarding this ??)

For the past 14 years I have always Logged my Engine time as "Engine on..... to Engine Off" (I figured this has to be the most accurate / honest way of doing it ??)

However, having just bought another aircraft I noticed one of the previous owners have logged the Engine time using the "Hobbs" type meter built into the RPM Instrument...... i.e Startup @ Hobbs 0576.23 to Shutdown @ Hobbs 0577.16 would be logged as 0.93 Hrs

Which of the above methods is the "Correct / Proper" way of logging it ?

Why am I asking this ?? - I am well aware that the Hobbs meter only records accurate time when the engine is at normal / cruise RPM, and as all flights have normal Warm up / Cool down periods (Low RPM) a typical "1 Hour Engine run" for a 45 minute flight would possibly only show as 50 mins "Engine time" on the Hobbs meter......... in which case it would be quite possible for the Pilots logbook time (Brakes Off to Brakes On) to actually be longer than the Engine Time (if using the Hobbs meter), which would look a bit ropey from an accuracy point of view ?

When I did my PPL training 20 odd years ago..... I was taught to log Engine Hrs as actual time "Engine on to Engine Off"....... Pilots Logbook time as actual time "Brakes Off- Brakes On"..... and Aircraft Time as actual time "Take-Off to Landing".

Any experience from you all, greatly appreciated !

Hello Andrew,

I've operated a number of light aircraft over many years and simply used "brakes off/on" for my logbook and "take-off/landing" for both airframe and engine. All with the express agreement of my engineers and maintenance organisation.

Regarding the engine follow the manufacturer advice. For the most common types it is air borne time but for some engines its approval is the actual start up to shutdown hours. The airframe standard is most commonly airborne time. The most common Hobbs (Datcon) meter is electric and is activated by the engine pressure so it is very close to start up to shutdown (there are some simple types that are activated immediately by the master switch). The law states that flight commences from when the aircraft moves with the intention to fly and ends when the aircraft comes a halt after landing. For airborne time it is common to keep it simple and to deduct 0 .2 from start up to shut down times allowing for non flight taxying time, this simpler method means that there is no need to note airborne and landing times although some do. It is the tacho that varies with RPM (not the Hobbs meter) so from start and during taxying at low rpm it records very little change over time. It is common therefore for non profit ops such as group owned aeroplanes to use the tacho for logging as it is very close for the average airborne flights of a short duration. The tacho is optimised to a constant 2300rpm over 1 hour (known as a 'tacho hour'). On longer flights of over two hours say (not precise) the tacho can be close to the clock hour or even exceed it if cruise is at a high rpm. The pilot should always log the flight time (see above) in their logbook distinct from the engine and airframe that is defined in accordance with the manufacturer .

Many clubs charge start up to shut down but retain the log books for its own use and record the airborne time (or as required by the manufacturer) for maintenance cycles. All the above method are acceptable to the CAA.

I look to our maintainers for this. With our Lycoming powered aircraft, they require airborne time for the airframe and engine, which is recorded in the airframe and engine log books and counts towards the Time before Overhaul for the engine.
Curiously, our microlight maintainer (for the C42) insists that engine and airframe wear should be counted from startup to shutdown, so quite different!
Now we come to the thorny issue of what do we charge against? With the C42, it's easy, start to stop, as recorded by the timer powered by the master switch.
I've been in groups where charge is made against the tacho, which encourages everyone to use sensible power settings. The problem here is that the price is apparently higher per hour, which requires the group members to understand that for every hour in their log book (chock to chock) they'll only be paying .8 or so. With a school or bigger Club, people won't understand that, so we have a chock to chock price. We also need a mechanism to stop people claiming that they flew for less time than they did so they don't have to pay as much. Thus, we have a timer in the Lycoming aircraft, NOT the tacho, which is activated by the master switch. They pay against this, whatever they might say about 'I was only 50 mins' when the timer shows an hour. We use the tacho time for maintenance records, acceptable to our maintainers.
Nothing is ideal here. In the States, I've heard of commercial pilots only being paid for when the undercarriage is retracted, leading to the inevitable late extension and expensive and noisy scrape along the runway.
TOO

Light aircraft - Take-off to landing

Microlights - engine start to engine stop

Aircraft approved for maintenance on tacho - tacho hours.

I have never used Hobbs, as in the vast majority of installations, all that's telling you is time with the battery master switch on.

I suspect that the OP may be confused about the difference between tacho and Hobbs?

G

That can be the case but the standard is that the Hobbs is activated by oil pressure so not only the master switch. In the case of the Rotax engines, commonly installed in microlights, the manufacturer stipulates start up to shut down and this is logged in the engine logbook. Therefore the Hobbs/Datcon meters activated by oil pressure do actually reflect this requirement. It isn't a matter of being a microlight. This is the case whatever type/class the engine is installed. The Continental 0-200 is commonly installed in microlights and airborne times are logged in accordance with the manufacturers approval. Whatever class of aeroplane the engine is installed in it is the manufacturers design approval that applies. I have never known of an engine that is stipulated to be maintained on tacho albeit this is the simplest and unambiguous method.

Interesting, I've heard that an oil pressure switch Hobbs is possible, but I've never actually seen such an installation.

Maintenance on tacho is pretty much universal in US GA, although less common elsewhere.

G

Engine time is logged by the tach.

Lots of ways to log everything else, but engine is by tach.

If you don't have a tach, then you can use any system you can defend!

It is misleading to use personal experience as the norm. When leasing aeroplanes the lessor has normally charged on tacho hours as its the least likely to be fiddled and therefore required maintenance to follow that. Having owned and operated my own flying club/school and aeroplanes for in excess of 30 years I have otherwise never used the tacho for maintenance although I acknowledge that many owners/operators do.

I think you will find that mechanical tachometers are produced with various rpm for time equivalence. Some electronic tachometers accumulate elapsed hours from engine start to engine stop with no option to base hours on rpm.

Garmin G3X Touch, which records engine and airframe hours, allows the installer to define how each time shall be measured. If rpm based is chosen then the rpm for 1 tach hour = 1 elapsed hour can be specified by the installer.

FAA definition - 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."

ref 14 CFR 1.1 General definitions.

I agree that it's common in USA to use tach time as time in service but that's not what FAA specifies.

Many, if not most heavier piston twins use a squat switch to activate the Hobbs so that waiting in line at a busy airport doesn’t count. Tach time isn’t generally displayed on a dual needle instrument. Burning Hobbs time when the master is on but the engines aren’t is just stupid.

FAA Code of regulations

Flight time means:

(1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing; or

(2) For a glider without self-launch capability, pilot time that commences when the glider is towed for the purpose of flight and ends when the glider comes to rest after landing.

This is exactly the same as the UK. The manufacturer stipulates the the maintenance cycle and how it should be calculated.

The Aircraft Tachometer

The mechanical 'tacho' measures the rotational speed of the engine drive shaft. It can be optimised how you require it to be. Speed = distance/time. It is usual for this calibration to be optimised circa a speed of 2300rpm (rotations per minute). With most light aeroplane operations the optimum cruise rpm is commonly operated around this figure. Of course, for the time spent on the ground the rpm will be much less. For flights of 1-2 hours the tacho hour will only equate to around 50 minutes or 0.8 of an hour owing to the ground time much lower rpm. For longer flights the tacho hour and clock time become very close to being matched. If you operate at much higher RPM then this match will also be true even for shorter flights.

The rpm also = engine care. Over speeding the engine can cause severe damage and for this reason monitoring the engine speed in accordance with the engine limitations is crucial. Too low and this can lead to plugs fouling which can also be a cause of engine failure.

There are units that allow you to chose the clock or switch to the tacho source. RPM is always critical. The above is not a tachometer.

To add to the above…

There are mainly two different time values (flight time & time-in-service) found within ICAO and other CAAs, each with their own definition and usage. However, in general, most CAA guidance allows a single recording method for both requirements.

In the case of maintenance tracking, ie., engine times, the preferred value and definition is time-in-service (TIS) as it gives the best bang for buck on maintenance related costs. However, since true TIS can be harder to record, the best conventional method for mx would be to use TACH time if you have a recording tachometer.

The reason is a mechanical tach is calibrated to a specific RPM and is only accurate at that RPM. So any slower engine run time like during taxi will be “prorated” at the slower RPM. But its closer to true TIS. Unfortunately with a digital tach you will lose most of that "prorating."

The least preferred conventional method to record mx TIS would be using a HOBBS especially if you do not have an oil switch in line to only record with the engine running. However, if you want to record flight time or charge for flight time the HOBBS is the better option as it gives you more for your dollar. If that makes sense.

That said, the most accurate method to record mx TIS would be to have a HOBBS with a wired squat or WOW switch that would only record true TIS once the wheels broke ground. Unfortunately if you used this method for flight time it would cheat you based on that accepted definition.

Or you could go old school and simply use your watch for all times.

When I joined a Group in 1990, we recorded from our watches. There were problems. We moved to tach. If someone forgets to log, it can be recovered. No cheating possible. Hourly charge was adjusted to tach.
it's very close to watch time, and, as recorded to 2 decimal places on present tach, more accurate than nearest 5 minutes, as usually used.

Tach seems the most logical - as it measures how much the engine has worked fairly accurately. Drive her hard, it'll turn more quickly. Drive her slow and gentle and the tach numbers will follow.

It works for forklift trucks, generators and who knows how many other devices/vehicles...

Thankyou everyone - some very helpful responses & very informative.

Genghis the Engineer - you are quite correct, I was (incorrectly) referring to my Tacho Time counter as a "Hobbs Meter" which I now know is an entirely different item.
(Neither of my aircraft are fitted with Hobbs meters - both just have the integral Tacho Time counters, both display to 2 decimal places are mechanically driven fitted to Continental C90s).

"Wrench1" - In the interest of keeping things as simple as possible (and as both aircraft are privately owned so no syndicate aircraft time / charging complications) - I will continue to log all times as per "Wristwatch" times - so "keeping it "Old School" as you say.

Ultimately - this will increase the engine time slightly more than "Tacho counter" time would, I am quite happy to carry out maintenance a few hours earlier than otherwise necessary.
I will continue to log the Engine time in the logbook as per Wristwatch times (so Engine on to Engine off) but will also note the Tacho Counter time after flight so future "Custodians" of the aircraft can have that figure also.... and then they can choose how they want to Log engine time going forward.

Much appreciated for all the replies. Thanks again !

Why? When a tacho is unavailable it is quite reasonable to deduct 0.2 or 12 minutes as representing ground time and is certainly acceptable by the UK CAA.to be entered into the aircraft log books; unless the aircraft/ engine manufacturer stipulates otherwise.