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The short answer
Hobbs time is real time the engine runs; tach time is tied to RPM and advances slower at low power. Hobbs is typically higher than tach for the same flight. Many maintenance intervals are based on tach time, so the safest habit is to read and log both after every flight and apply whichever a given inspection or overhaul calls for.
Hobbs and tach time, defined
Two meters in the panel measure how much your aircraft has flown, and they almost never agree:
- Hobbs meter: runs on a clock whenever the engine (or oil pressure / airspeed switch) is active. One hour of Hobbs is one real hour.
- Tachometer time: driven by engine RPM and calibrated to a cruise reference. At taxi and reduced power it accrues slower than the clock.
- Result: for a typical flight with taxi and pattern work, Hobbs reads noticeably higher than tach.
Which time drives maintenance?
There's no single answer; it depends on the item, and that's exactly why owners get tripped up:
- Engine overhaul (TBO) and many manufacturer inspections are commonly tracked on tach time as a proxy for actual engine wear.
- Calendar items (annual, ELT battery, transponder/pitot-static checks) are driven by date, not hours at all.
- Rentals and some programs bill on Hobbs because it reflects real operating time.
The practical takeaway: capture both numbers, and let each maintenance item reference the clock it's actually written against.
How to log your hours
Tracking hours is simple discipline. The value is in never missing a reading:
- 1
Read the meter after each flight.
Note the Hobbs and/or tach value at shutdown.
- 2
Record it with the date.
A reading is only useful when it's tied to when it was taken.
- 3
Be consistent.
Always log the same meter for the same purpose so your history is comparable.
- 4
Let the hours drive the schedule.
Tie your readings to maintenance intervals so the next-due math happens for you.
How Maggneto handles it
Maggneto records both Hobbs and tach time: you log the reading and it does the tracking. For twin-engine aircraft it tracks a tach per engine. Those readings then feed your maintenance schedule and oil tracking automatically, so the hours you log on the ramp turn straight into accurate due dates.
Stop doing the hour math by hand
Log Hobbs and tach in seconds and let Maggneto turn every reading into accurate maintenance due dates and oil burn rates. See the flight time tracking product.
Frequently asked questions
What is the difference between Hobbs and tach time?
Hobbs time is real (clock) time the engine runs; it accrues at a constant rate whenever the engine is on. Tach time is tied to engine RPM, so it advances slower than real time at low power (taxi, descent) and near real time at cruise RPM. Hobbs is usually higher than tach for the same flight.
Which one is used for maintenance?
It depends on the item. Many manufacturer inspection and overhaul intervals are based on tach time (a proxy for engine wear), while rentals and some maintenance programs bill or track on Hobbs. Track both and apply whichever the specific maintenance item calls for.
How do I track aircraft flight hours?
Read the Hobbs and/or tach meter after each flight and log the value with the date. Maggneto lets you record both, then uses those readings to drive maintenance due dates automatically.
Why does tach time advance slower than Hobbs?
A mechanical tachometer is calibrated to a reference RPM. Below that RPM it under-counts relative to the clock, so time spent taxiing, climbing at reduced power, or descending accrues less tach time than Hobbs time.