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12 Answers

How calculate flight hours

Asked by: 13644 views Commercial Pilot, General Aviation, Private Pilot, Student Pilot

How do you compute flight hours for the flight book? Example: starting with engine runup, or when leaving ground (same thing when landing: when engine is stopped or when wheels touch down)? Or whatever else?

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12 Answers

  1. Kate Knoblauch on Jan 25, 2011

    You don’t have a hobbs meter in the airplane?  Counts from the moment the propeller starts moving.

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  2. MaggotCFII on Jan 25, 2011

    Adding to the above, Hobbs or Clock, not the Tach!
    And from:
    FARs, Part 1, Definations and Abbreviations, 1.2 General Definitions.

    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.

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  3. skyboyCFI on Jan 25, 2011

    Maggot hit it on the nose. According to the definitions, time doesn’t start until your moving. Everyone logs Hobbs though. I’ve seen some flight schools rip off their students by wiring the Hobbs to the master switch instead of the engine. Make sure that’s not the case otherwise the actual cost can be 10% higher than competitors that wire it right.

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  4. Kent Shook on Jan 25, 2011

    From FAR 1.1:
    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.”
    There is a (2) segment to that for gliders. For airplanes, when you taxi from the tiedown until you taxi back into the parking spot is loggable as flight time. Since it’s generally very close to the amount of time the engine is running, most people will log their flight time based on the Hobbs time they put on the aircraft.

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  5. Kent Shook on Jan 25, 2011

    Wow, I need to answer these questions faster. 😉

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  6. John A Lindholm on Jan 26, 2011

    Real simple…..  immediately after engine start, let the aircraft “roll” a few feet and then check your brakes to a stop.  That let’s you count the same time as Hobbs if it is connected to an oil pressure switch.  Engine run time on the ramp does NOT count unless the aircraft has moved.  When you are an airline pilot, you can count your time from “push back” from the gate until you hit the gate after landing…. more importantly, pay time.

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  7. Brian on Jan 26, 2011

    This is interesting. Aren’t most of us recording hours based on the hobbs time? A time that starts as soon as the master is switched on. I know I did, and everyone who trained at the college as well as the FBO’s in my local area record in this manner. According to this regulation we are giving ourselves a few minutes of extra flight time for each flight. I’m referring to the time for preflight, engine startup, and the short time after shutdown that likely add to about 3-5 minutes each flight. A time we, or at least I, record, but the engine isn’t even running. 
    Are people here using their tach time to record flight hours? I’ve never had a DPE stop any student, or myself, over using hobbs times. Is there an LOI to accompany this regulation that addresses this? I came up empty. Thanks.

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  8. skyboyCFI on Jan 26, 2011

    Few hobbs are wired to the master switch. If it is, you’re being ripped off.

    Read above again. The ‘definition’ of flight time is when the aircraft moves under it’s own power, for the purpose of flight. If you go practice taxi, never intending to fly, the time is actually zero. That is the answer.

    However, pretty much everyone logs the time on the hobbs. It’s a very acceptable and common practice, although it’s not inline with the definition.

    Log hobbs, it’s what you pay for. You pay per flight hour based on hobbs, you log Hobbs. Most school charge for instructor by hobbs even though he’s there for preflight.

    If you get a examiner that questions a very few seconds after you start your engine as log time, he’s a jerk and will probably fail you for parting your hair on the wrong side. And if your school is wiring the Hobbs to the master switch and not the engine oil presure sensor (so the Hobbs won’t start running until the engine starts) then your school is cheating you, for flight & instructor time.

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  9. skyboyCFI on Jan 26, 2011

    Oh, FYI, the tach time is the aircraft maintenance time. All maintenance and inspections are based off the tach. Tach measures engine time. Over-haul requirements are based on engine time. It’s almost always less then Hobbs but can be higher on long flights running high rpm’s.

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  10. Kent Shook on Jan 26, 2011

    Tach time doesn’t give you an accurate flight time – It’s always somewhat different depending on what you’re doing. My club charges by tach time, so when I first joined I kept track of tach vs. hobbs for a while. VFR cross countries are the worst ratio (I’ve had flights as low as 1.07:1) but when you’re in the pattern or shooting approaches, it’s quite easy to get 1.4 hours for every hour of tach time. The best ratio I’ve ever gotten was on a quick 3-trips-around-the-pattern flight: 0.6 on the Hobbs, 0.2 on the tach. 
    So, I suggest that if you don’t have a Hobbs, or if you want to be super-accurate, you should use your watch and write down the start and stop times, and log that. If you do have a Hobbs, they’re not going to ding you for “having an extra minute of flight time on every flight” when the resolution of the Hobbs (and the logbook, for that matter) is only 6 minutes (0.1) to begin with.

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  11. James MacGregor CFI on Jan 28, 2011

    Hobbs is time from prop start to stop
    Tach is one hours on the clock for one hour of time ONLY when at 100% RPM, most cruse at 70% RPM so tach would be 30% less then hobbs
     WHAT TO LOG, log the hobbs, you log from when the plane moves for the purpuse of flight, the second the engine starts the plane will move a little (yea it’s probably only a 1/4 inch lol), but it does move, so thats what you log.

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  12. skyboyCFI on Jan 28, 2011

    Lmao!! Start the plane and it moved a centimeter. “Love it”. I’m all for that!!! :-p

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