Does a hobbs/tach need to be viewable from inside of the cabin?

schmookeeg

schmookeeg

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Mike Brannigan
I think I know this, but I'm suspicious that I've overlooked some oddball reg or requirement.

My panel has no dang room, and I've been casting about for things to adios or relocate.

I have a small bit of easy space I can create by moving the airframe hobbs from the copilot station to the nose baggage area, where the heater hobbs lives currently.

This plane has no tachometers, only this one little hobbs for hourmeter, so all of the maintenance logging relies on it. But.. I don't need to view it while flying around, only when contemplating maintenance actions.

Legal to move the thing? I think yes. But with 90% confidence only. :D

I don't really want to put it low on the pedestal. I could recess it under the bus bar I suppose. Actually there are a dozen annoying places I could reloc it to, but... this idea appeals to me for some reason.

Thx in advance for arguments and your most colorful "RTFM, Idiot" responses. :D
 
Nope! It’s not even a requirement by the FAR's to have a Hobbs meter. :)
 
schmookeeg said:
I think I know this, but I'm suspicious that I've overlooked some oddball reg or requirement.

My panel has no dang room, and I've been casting about for things to adios or relocate.

I have a small bit of easy space I can create by moving the airframe hobbs from the copilot station to the nose baggage area, where the heater hobbs lives currently.

This plane has no tachometers, only this one little hobbs for hourmeter, so all of the maintenance logging relies on it. But.. I don't need to view it while flying around, only when contemplating maintenance actions.

Legal to move the thing? I think yes. But with 90% confidence only. :D

I don't really want to put it low on the pedestal. I could recess it under the bus bar I suppose. Actually there are a dozen annoying places I could reloc it to, but... this idea appeals to me for some reason.

Thx in advance for arguments and your most colorful "RTFM, Idiot" responses. :D
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No tachometers??
 
FastEddieB said:
That seems off. “4) Tachometer for each engine” Is/are required for VFR flight.
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Yeah. I’m thinking he might be talking about Tachs that don’t have an ‘hour’ meter. The odometer so to speak. I’ve never seen one, but I suppose there could be.
 
NoHeat said:
Dumb question, maybe, but what’s a heater Hobbs, and what’s its use?
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I think all of the janitrol-derived heaters have pernicious ADs on them that need inspecting periodically (100hrs?) -- no idea when or why they were first put on (hopefully not to track future ADs :D ), but the heater has its own hour meter.
 
My old 47 didn’t have one at all back in the day- just has every flight it took in the airframe log for a number of years! :)
 
luvflyin said:
Yeah. I’m thinking he might be talking about Tachs that don’t have an ‘hour’ meter. The odometer so to speak. I’ve never seen one, but I suppose there could be.
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Tachs without hour meters are extremely common in multiengine aircraft. Especially since it's very common to have both engines displayed on the same tach.

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NoHeat said:
Dumb question, maybe, but what’s a heater Hobbs, and what’s its use?
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All a Hobbs meter is, is a clock that only runs when power is applied. A Hobbs is the brand name, and they are used in all kinds of applications. The Seminole I use for multiengine instruction actually has three - one for the heater (runs when the heater is turned on), one for maintenance (which runs off a squat switch, meaning it runs when the plane is airborne), and one for billing (which runs when the right engine has oil pressure).

The heater hobbs is necessary because there are various recurring ADs and inspections that must be done at every, say, 100 hours of heater operation. Obviously the heater hobbs doesn't move all summer.

The maintenance hobbs is used to track time-in-service for 100-hour inspections, oil changes, etc. Since the FAA allows almost any reasonable definition of time-in-service for these inspections, having it limited to when the plane is actually airborne certainly reduces the frequency, and therefore cost over time, of these inspections.
 
Some of the singles have tachs without hour meters. I just delivered an early 90s A36 Bonanza across the country. It had all the original factory equipment. No hour meter on the tach. Only a hobbs, which was not located on the panel.
Obviously there is a small difference in tach hours vs hobbs time. If there is a tach hour meter, it’s used as the trigger for scheduled maintenance. If it only has a hobbs then it had to be used for maintenance scheduling requirements.
So, if you only have a hobbs, you’re probably going to accomplish maintenance a bit sooner than if you have a tach hour meter.
I’m kinda surprised there’s not some standard for this due to the maintenance requirements. Maybe there is?? I’m not aware of any.
 
Jdm said:
Some of the singles have tachs without hour meters. I just delivered an early 90s A36 Bonanza across the country. It had all the original factory equipment. No hour meter on the tach. Only a hobbs, which was not located on the panel.
Obviously there is a small difference in tach hours vs hobbs time. If there is a tach hour meter, it’s used as the trigger for scheduled maintenance. If it only has a hobbs then it had to be used for maintenance scheduling requirements.
So, if you only have a hobbs, you’re probably going to accomplish maintenance a bit sooner than if you have a tach hour meter.
I’m kinda surprised there’s not some standard for this due to the maintenance requirements. Maybe there is?? I’m not aware of any.
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Depends on how the Hobbs is wired.
 
Understand it can be wired (activated) in different ways. Electric, or electric w/oil pressure sensing seem to be the most common type. Either way, Hobbs results in a different reading than tach hours by some small amount. I don’t know of any way to obtain the same value from a Hobbs that would register on a tach hour meter.
 
My Hobbs is in the glovebox...
 
Jdm said:
I’m kinda surprised there’s not some standard for this due to the maintenance requirements. Maybe there is?? I’m not aware of any.
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There is. It's in 14 CFR 1.1, "Definitions".

"Time in service, with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing."

So a Hobbs that is wired to a squat switch is pretty much the only accurate method. All others, including using tach time, are estimates. However, tach time is a widely accepted, and FAA-sanctioned, method of tracking this time, since it's close enough (and in most operations will be greater than "squat switch Hobbs" time, meaning the inspections happen slightly more frequently, so it's not a problem).
 
Interesting, thanks for the definition. Now I’m thinking about AD’s. Seems like I remember some of the spar inspection times worded differently. I’ll have to take another look at that.
 
RussR said:
All a Hobbs meter is, is a clock that only runs when power is applied. A Hobbs is the brand name, and they are used in all kinds of applications. The Seminole I use for multiengine instruction actually has three - one for the heater (runs when the heater is turned on),
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Thanks.

I have another dumb question: what is this heater, and why does a multi engine plane have one? Does it heat something in the engine, like carb heat? Or is it for deice?
 
NoHeat said:
have another dumb question: what is this heater, and why does a multi engine plane have one? Does it heat something in the engine, like carb heat? Or is it for deice?
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It’s a gas combustion heater, commonly located in the nose compartment. They’ve been around forever. The problem is, they can be dangerous if they begin to deteriorate. They usually have their own hobbs to keep up with specific inspections required for the heater. The heater hobbs only clocks when the heater is in use. The inspection is somewhat expensive, so it’s important to keep up with the time separately.
They work great. It’s for heating the cabin for comfort. We have one in the Aztec that I fly. Very common on light twins.
 
It heats people. It wouldn't work very well to wrap a muffler (my plane doesn't even have mufflers) and run a scat duct all the way in from the nacelle.

Burns 1.5 gph, super toasty. :D
 
The Cessna 195 puts one of those gasoline combusting cabin heaters under the rear seat. I have vowed that if we ever get that project flying, I will never, ever, turn it on. Nope.
 
I think they are a lot better these days than before. We’ve never had a problem, but our maintenance is is top notch on that bird. If you’re not going to use it maybe consider deactivating and removing the weight. At least 20 lbs!
 
As noted the Hobbs is not a required instrument, even if you don't have a recording tach. So yea, you can put it in the baggage compartment.
 
Later model Bonanzas do not have recording tachs. My Navion didn't have one for a while either. We used the Hobbs for maintenance time.

As pointed out by others, it's not a required instrument for flight.

Some airplanes have NO device recording time in them. Other more primative means (pilot's watch) used for time in service.
 
Was out at the hangar yesterday, thought this might be interesting… Here’s the engine Hobbs meter in a P-51 Mustang just aft of the Merlin engine.

34C70AF9-DA67-48C7-B454-D3404800137C.jpeg
 
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