Guide
Hobbs or tach: which meter should the club bill on?
Two meters, two different numbers for the same flight, and a club rule that was probably set by whoever was treasurer in 2011. Here is what each one measures and what changing basis does to the money.
What each meter measures
The hobbs meter is a clock. It is usually wired to an oil pressure switch or the master, so it runs whenever the engine is running, at the same rate as your watch. An hour on the hobbs is an hour of engine running, including the twenty minutes spent behind three aeroplanes waiting to depart.
The tachometer hour meter is geared to engine speed. It is calibrated to record one hour at a particular cruise RPM, so it runs fast above that RPM and slow below it. Taxi at 1000 RPM and it barely moves. Fly a long cross country at cruise and it tracks close to the clock.
On a typical training or club flight, tach time comes out lower than hobbs time, commonly in the region of eight or nine tenths of it. Pattern work with a long taxi diverges more; a two-hour cross country diverges less. The exact ratio is a property of your aeroplane, your engine and how your members fly it, and you can measure it from your own flight records rather than guessing.
What the regulations point at
Two definitions in 14 CFR 1.1 are worth having straight, because clubs mix them up constantly.
- Flight time, the thing a pilot logs, runs from the moment the aircraft moves under its own power for the purpose of flight until it comes to rest after landing. That is block time, and a hobbs meter is a decent proxy for it.
- Time in service, the thing maintenance records run on, is the time from the moment the aircraft leaves the surface until it touches down at the next point of landing. That is airborne time, and it is shorter than both hobbs and, usually, closer to tach.
Neither meter is time in service exactly. Clubs commonly use tach as the working approximation for maintenance intervals and hobbs for pilot logging, and record both. Whatever your club does, write it in the rules and be consistent, because an inspection interval computed on one basis and flown on another drifts quietly.
The billing argument, both directions
| Billing on hobbs | Billing on tach | |
|---|---|---|
| Members find it | Easy to understand. It matches the clock and the logbook. | Harder to predict before the flight. |
| Ground time | Charged. A long hold on a hot day costs the member. | Barely charged. Cheap to sit and wait. |
| Relationship to engine wear | Loose. Idling and cruise cost the same. | Closer. The meter follows RPM. |
| Revenue per flight | Higher for the same rate. | Lower for the same rate, so the rate has to be higher. |
| Maintenance intervals | Overstates time in service, so inspections come round early. | Closer to time in service. |
| Disputes | Rare. Everyone can read a clock. | More common, until people trust the meter. |
Converting a rate when you change basis
This is where clubs lose money without noticing. If your fleet averages 0.9 tach hours for every hobbs hour, then switching from hobbs to tach at the same rate cuts about 10% of your flying revenue while the costs stay exactly where they were.
The correction is arithmetic. Take your current rate, divide by the ratio of tach to hobbs that your own records show, and that is the tach rate which yields the same revenue.
Measure the ratio from your own flights over a season rather than borrowing someone else’s number. In FlightWay both readings are captured on every flight, so the ratio is a report rather than a research project.
What we would do
Bill on the basis that matches how your aeroplanes accumulate cost, which for most piston clubs is tach, and set the rate deliberately for that basis. Record both meters on every flight regardless, because the pair is what lets you check the ratio, check the maintenance interval and answer a member who thinks the charge is wrong.
Then hold the basis still. A club that changes basis every time the committee turns over cannot compare a year to the year before it, and that comparison is the only early warning that a rate has fallen behind.
FlightWay stores the rate and the basis per aircraft, so a club billing the Cherokee on tach and the Cub on hobbs is a setting rather than a monthly act of memory. How flight logging works.
Last updated 18 August 2026.