My engine has done 1600hrs airborne time but the “hobbs” meter (in my case a time counter which runs when the RPM is over 1200) is reading 1920hrs.
Most people maintain according to the meter…
Maintenance according to airborne time is 100% legal on N-reg and EASA-reg.
Maintenance according to airborne time is 100% legal on N-reg and EASA-reg.
That’s what I’ve always done. For EASA reg you have to have this specified in Maintenance Program and refere it to Maintenance Manual.
I don’t even have an idea what the (2) meters in my plane say. I do everything strictly by flight time.
When selling aeroplanes I have had many an argument with purchasers who want to know why the Hobbs is different to the logs. It seems to be a US thing, they just won’t believe the logs, so it may be correct to use airborne time but it has caused me a lot of problems in the past.
I’ve seen the opposite problem – the Hobbs was much, much lower than the time recorded in the logbooks. Guess which one the seller advertised as the aircraft total time?
One problem is that all the electronic meters can be adjusted, or reset. The one in my TB20GT can be; Air Touring had the adaptor for doing it. This was needed because these things do fail (I had two fail early on) and the replacement should be reset to read what the old one read.
So do you trust the logbooks, or the meter? I honestly don’t know.
Logbooks do get forged, for sure. People know what the buyer will be looking for e.g. on a very low time plane (I recall seeing a 12 year old TB20GT with ~300hrs on it – very likely to be full of rust) the buyer will be looking for regular usage, and the 300hrs could conceivably be spread over the 12 years to look “OK” whereas in reality this is highly unlikely.
Many thanks for posting that, Guillaume. Unfortunately I can barely read it, let alone google translate it 
Can you or someone translate the relevant part? It’s very interesting because there are so many different hour counters in existence (oil pressure, oil pressure over X PSI, rpm over X, etc).
I wonder how they frame the wording to deal with all that, because one could also use the “airborne time” reading from some instruments.
Especially for a TB20 which is …. French made! And Socata never said anything about this to me.
It says that France defines “flight time” just like ICAO Annex 6 Chapter 1 does :
Flight time (aeroplanes) : The total time from the moment an aeroplane first moves for the purpose of taking off until the moment it finally comes to rest at the end of the flight.
Note.— Flight time as here defined is synonymous with the term “block to block” time or “chock to chock” time in general usage which is measured from the time an aeroplane first moves for the purpose of taking off until it finally stops at the end of the flight
It says that GA should use flight time to conduct maintenance.
Airborne time may be acceptable for commercial air transport.
Legal reference here (in French only)
Be careful, this is a document of 1991. That was before EASA and even before JAR. Things may be different now. Right now I don’t have the time (or nerves…) to search for the relevant references in the EASA documents, but “my” flying school still uses air time for aircraft related things and block time for crew related things, just as under JAR. The same in “my” commercial GA operation.
Anyway, as the “Hobbs” meter or equivalent is very uncommon around here, whatever you write down as block time is essentially up to you.
