Here's a bonehead question. When stating total time on airframe/engine, does one quote Hobbs, or Tach?
Here's a bonehead question. When stating total time on airframe/engine, does one quote Hobbs, or Tach? For me, the difference is considerable.
Hobbs.....442.22
Tach.......364.22
According to the FAA it is up to the owner to determine and record aircraft time. You could use a stop watch for that matter, but the normal for non commercial use is tach time.
george
Here's a bonehead question. When stating total time on airframe/engine, does one quote Hobbs, or Tach? For me, the difference is considerable.
Or, you can look at your watch 4 times during the flight......... Start, Roll, End of rollout, and stopping before shutdown.
I like to be simple. Hobbs time for everything. Although some may think it is conservative for maintenance, I don’t, as if engine is turning things are wearing out in the engine. As for pilot time, Hobbs is also correct as butt in seat with propeller turning is pilot time as you are operating the plane.
A bit of drift
In buying I would want to know cycles as well for both engine and airframe. 500 hours with 1000 engine starts and take-offs and landings is much different than 500 hours with 250 engine starts and take-offs and landings. I don’t know if anybody really ever advertises cycles for GA aircraft. I don’t track mine, per say, but I keep a flight log of each flight with fuel stops, oil adds, and type of flying (altitude and general activity including number of TOs & Landings) that I can go through that flight log and count cycles if asked.
So just to play devil's advocate...I did a quick search in both the engine and prop manuals, and nowhere could I find any reference to anything called "tach time" for maintenance intervals (might be there and I missed it). What they both specify are "hours"...e.g., "Accomplish a detailed inspection at 100 hour intervals not to exceed twelve (12) calendar months..." (Hartzell prop manual).
FAA Part 91.205 says that all general aviation aircraft must have an operational airspeed indicator, altimeter, fuel gauge and a magnetic direction indicator. Each engine on the aircraft must also have a corresponding oil pressure gauge, temperature gauge and tachometer as well as other basic equipment for the safe operation of the aircraft.
So, while a hobbs meter is not required, a tachometer is. One could quite easily interpret this to mean.. If the FAA wanted us to track hours on parts, they'd require a hobbs meter if that's how they wanted us to measure hours. Instead, they've chosen to use a tachometer to measure time on said parts..
Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer
FAA Part 91.205 says that all general aviation aircraft must have an operational airspeed indicator, altimeter, fuel gauge and a magnetic direction indicator. Each engine on the aircraft must also have a corresponding oil pressure gauge, temperature gauge and tachometer as well as other basic equipment for the safe operation of the aircraft.
So, while a hobbs meter is not required, a tachometer is. One could quite easily interpret this to mean.. If the FAA wanted us to track hours on parts, they'd require a hobbs meter if that's how they wanted us to measure hours. Instead, they've chosen to use a tachometer to measure time on said parts..
1. FAR 91.205 does not say ‘all’ aircraft. EAB are excluded.
2. A tachometer measures RPM. Some, but not all, may have a ‘tach-hour’ function.
You're right that 91.205 excludes EAB aircraft, but your ops limits probably reference 91.205 anyhow.
Regardless, this discussion isn't specifically limited to EAB... As a matter of fact, one could actually argue that TBO etc applies even less to EAB, since the engine itself may be experimental
Your Ops Lims will probably only reference 91.205 when talking about night or IFR flight - not Day VFR, for which nothing in 91.205 is required.
So just to play devil's advocate...I did a quick search in both the engine and prop manuals, and nowhere could I find any reference to anything called "tach time" for maintenance intervals (might be there and I missed it). What they both specify are "hours"...e.g., "Accomplish a detailed inspection at 100 hour intervals not to exceed twelve (12) calendar months..." (Hartzell prop manual).
If I were to take a lawyerly approach to this, I'd say that means hours of operation, not hours of operation scaled by some arbitrary factor (arbitrary in that everyone can pick their own "preferred" RPM for computing tach time).
I don't think it makes a hill of beans worth of difference if you're taking good care of your engine and prop in general, but we have an awful lot of discussions here that usually involve some aspect of "what does it say in the manufacturer's manual?". Well, Lycoming and Hartzell don't say a thing about computing something called "tach time" and using that for maintenance intervals. They just specify "hours", which to me means the common English use of the term...the number of hours part X has been operated. Period.
As Mike Myers used to say on SNL in that sketch..."Discuss!"