A member comes back from an hour's local flight, picks up the flight sheet and finds 1.4 hours on it. They were in the air for 60 minutes. They know they were, because they watched the clock all the way round.
The flight sheet and the member are both right. The difference is which clock your club bills on: the Hobbs, the tacho, airborne time or brakes-off to brakes-on. Two clubs can charge the same rate for the same aircraft and still send a member very different bills. The clock also decides who pays for the taxi, the power checks and those twenty minutes at the hold, the member or the club. Pick it by accident and your hourly rate quietly stops meaning what you think it means.
Our view, for most clubs, is to bill on the meter the aircraft already has (Hobbs or tacho) and set the rate from a few months of that meter's readings. We'd only move to airborne time if your ground waits are long and unpredictable, and only once you've raised the rate to carry them. And we'd never compare a rate with another rate unless both are charged on the same clock.
The sums below carry no currency, so they work in pounds, euros or dollars.
Hobbs, tacho, airborne and brakes-off compared#
Hobbs#
An hour meter on the panel. It counts real time, in hours and tenths, whenever it's switched on. What switches it on depends on the wiring. Usually that's oil pressure, so it runs whenever the engine does. Sometimes it's the master switch, and occasionally an airspeed or undercarriage switch that only runs it in the air. Have a look at how yours is wired before you write a rule around it, because a meter on the master switch charges for the time the pilot sits there with the radios on before start.
Tacho#
The recording counter built into many tachometers (the tach, in North America). This one counts engine revolutions rather than time. It reads one hour when the engine has turned at the meter's set speed for an hour. Below that speed it runs slow, and above it, fast. So a flight with a long taxi, plenty of idling and a gentle descent will usually read less than the clock on the clubhouse wall. A long climb at high power can read more.
Airborne#
Take-off to touchdown, from the pilot's watch or the times the tower or radio log records. You don't need a meter. You do need someone to write the times down honestly.
Brakes-off to brakes-on#
From the moment the aircraft first moves under its own power to the moment it stops at the end of the flight. You'll also hear it called block time or chock to chock. Like airborne time, it comes from a watch and the flight sheet.
How regulators define flight time#
Regulators define flight time for pilots' logbooks and, in some countries, a separate time for maintenance records. None of it tells a club what to charge by. But it does explain why a member's logbook, the aircraft's tech log and the bill may not agree.
| Country | Pilot flight time | Time for maintenance records |
|---|---|---|
| United States, 14 CFR 1.1 | Starts when the aircraft "moves under its own power for the purpose of flight" and ends when it "comes to rest after landing" | Time in service: from the moment the aircraft "leaves the surface of the earth until it touches it at the next point of landing" |
| Canada, CARs 101.01 | From the moment the aircraft "first moves under its own power for the purpose of taking off" until it "comes to rest at the end of the flight" | Air time, for technical records: from leaving the surface until contact with the surface at the next point of landing |
| New Zealand, CAR Part 1 | From when the aircraft "first moves for the purpose of flight" until it "comes to rest at the end of the flight", including pushback, taxiing and holding | Time in service: from "leaving the surface until touching it again on landing" |
| United Kingdom and Ireland, Part-FCL, FCL.010 | For aeroplanes, from when the aircraft "first moves for the purpose of taking off" until it "finally comes to rest at the end of the flight" (the UK keeps its own copy of the EU rule) | Not set by the licensing rule. Ask your engineer which hours your maintenance programme counts |
| Australia, CASR regulation 61.080 | Counts "the duration" of each flight, but does not say when the flight starts or ends | Set by your maintenance programme. Ask your engineer which hours it counts |
Where the rule does set a start and an end, brakes-off to brakes-on comes close to what a pilot logs. In the United States, Canada and New Zealand, the maintenance definitions describe airborne time. The Hobbs and the tacho match neither exactly. They're popular anyway, because they sit on the panel and nobody has to write anything down.
One flight billed four ways#
Back to that member and their one-hour local flight. Here's how the morning went.
| Event | Time |
|---|---|
| Engine start | 10:00 |
| Brakes off | 10:04 |
| Take-off, after taxi, power checks and a short wait | 10:16 |
| Landing | 11:16 |
| Brakes on | 11:22 |
| Engine stop | 11:23 |
The engine ran for 83 minutes, the aircraft moved for 78 and it was in the air for 60. A Hobbs wired to oil pressure moves about 1.4. Brakes-off to brakes-on is 1.3, and airborne is 1.0. Say the tacho moves 1.2, a little under the engine time. That's normal for local flying with a taxi and a low-power descent, though yours will depend on the power used and the speed the meter is set to (which is why the rule further down asks you to record both meters).
Now charge all four at the same rate of 230 an hour dry:
| Clock | Hours | At 230 an hour | Rate that gives a bill of 230 |
|---|---|---|---|
| Hobbs | 1.4 | 322 | 164 |
| Brakes-off to brakes-on | 1.3 | 299 | 177 |
| Tacho | 1.2 | 276 | 192 |
| Airborne | 1.0 | 230 | 230 |
Same hour of flying, and the bill moves by 92 depending on the clock. Look at the last column, because this is the bit most people get wrong. A Hobbs rate of 164 can be exactly the same price as an airborne rate of 230. A rate only means something next to the clock it's charged on, so the club down the road with the "cheaper" rate may not be cheaper at all. Our hire rate guide shows how to turn a cost per engine hour into a cost per charged hour using your own records.
Who pays for time waiting at the hold#
Now take the same flight on a busy Saturday. There's a queue at the hold, and the member spends 25 more minutes on the ground waiting to depart. We'll keep the rates from that last column, so the quiet day costs 230 on every clock.
| Clock | Hours | Bill |
|---|---|---|
| Hobbs | 1.8 | 295 |
| Brakes-off to brakes-on | 1.7 | 301 |
| Tacho, say | 1.3 | 250 |
| Airborne | 1.0 | 230 |
Brakes-off ends up slightly dearer than Hobbs here, even though it counts fewer minutes. That can look odd at first. The Hobbs rate is lower (it already allows for the minutes before the aircraft moves), so each extra minute on the ground costs more on brakes-off. The 25-minute wait adds about 71 to the brakes-off bill and 66 to the Hobbs bill.
So on the Hobbs or brakes-off clock, the member pays for the wait. On the tacho, the engine idling at the hold turns the meter at well under half speed, and the club soaks up most of it. On airborne time the club soaks up all of it, even though the engine ran and burned fuel the whole time.
Which clock suits which club#
| Clock | Who pays for ground time | Needs times written down | Matches pilot logbooks | Matches maintenance hours |
|---|---|---|---|---|
| Hobbs | The member, from engine start | No | Roughly | No |
| Tacho | Mostly the club | No | No | Often used as a stand-in. Check your programme |
| Airborne | The club | Yes | No | Yes, under the US, Canadian and New Zealand definitions |
| Brakes-off to brakes-on | The member, from first movement | Yes | Yes | No |
Billing on the Hobbs#
Nobody has to write anything down, and nobody has to trust anyone. That suits a busy fleet flying from one airfield, where ground time is much the same from flight to flight. The catch is what it does on the ground. A pilot who can see the meter ticking over may rush the power checks, or skip warming the engine on a cold morning. We'd say plainly in your rules that the checks are part of the flight and the rate allows for them.
Billing on the tacho#
This is the one that catches out clubs doing a lot of training. A student flying circuits spends much of the flight at low power, so the tacho reads light against the clock, and the hour on your rate card covers more real time than it looks. If most of your flying is circuits and short local trips, measure the tacho against the wall clock for a few months before you set the rate. On long cross-countries at steady power the gap is much smaller.
Billing on airborne time#
Members like it, because they only pay for flying. It also suits an airfield with long or unpredictable queues for departure. But the club carries the cost of ground running, so the rate has to be high enough to cover it. The rule needs a source for the times too: the pilot's sheet, the tower's log or both. And if your maintenance hours are logged as airborne time, billing and the tech log will agree.
Billing brakes-off to brakes-on#
Use this one if you want the bill to match what members write in their logbooks, or if not every aircraft has a working meter. It charges for the taxi and the wait, but not for the minutes before the aircraft moves. Watch times need a rounding rule. They also need a habit of writing them down as they happen, rather than from memory at the end of the day when everyone's packing up.
Writing the billing rule on the rate card#
Whichever clock you pick, put these on the rate card and the flight sheet so nobody has to ask:
- The clock. "Charged on Hobbs time" or "Charged brakes-off to brakes-on". If the aircraft has a meter, say which one.
- The readings. Start and finish readings, or start and finish times, recorded on every flight, rather than the difference alone.
- Rounding. Meters read in tenths. For watch times, say how minutes become tenths, for example to the nearest six minutes.
- A fallback. What you charge by when the meter fails. Usually that's brakes-off to brakes-on from the flight sheet until it's fixed.
- Instruction. If an instructor is aboard, say whether instructor time runs on the same clock as the aircraft or includes the briefing.
- Any minimum. If you charge a minimum for a booking, say how much and on which clock.
If the aircraft has both meters, record both, even if you only bill by one. After a few months you'll know the real ratio between them for your flying. You'll be glad of that figure the next time the rate comes up at a committee meeting.
Charging flight time in Volanti#
A billing rule only works if it's applied the same way on every flight, by every pilot. In Volanti, the hours are recorded when each flight is completed, and the flight is priced at your rates and charged to the pilot's account straight away. Members see each charge, their balance and their statements in the pilot portal. See how charging works in billing and payments.