Hobbs

I saw this quote in a forum sig:

Student Pilot’s Prayer; “Dear Lord, if we must have an instrument failure today, please let it be the Hobbs Meter.”

For those who don’t already know the Hobbs meter is an hour meter which measures hours and tenths of engine running time. When you rent an airplane usually you are billed by Hobbs time and the ending Hobbs time minus starting Hobbs time is also what you log in your logbook. The exact mechanism varies but usually the meter is tied to an oil pressure switch or similar so when the engine starts the meter starts running.

When you own an airplane the Hobbs meter isn’t so important. The tachometer also contains an hour meter which is scaled relative to the engine RPM. It is designed so that it advances in real time if you are at a cruise RPM. This means that ground operations and lower RPM operations count less on the tach hour meter. The tach hour meter is useful for maintenance intervals like oil changes because it is a reasonable proxy for accumulated load on the engine.

All of this is good because the Hobbs meter in N52667 doesn’t work. Before departing Statesville we wrote it down along with the current time as backup for determining the flight time for logbooks. However, upon arriving in Hagerstown the Hobbs meter definitely hadn’t budged. A bit more math is required to figure out your flight time to log when you just have two absolute times to subtract (and decimalize the result) but it isn’t too much of a pain.

The quote reminded me of my hate of the Hobbs. If you are a renter pilot the worst case scenario is slow ground operations. On a nice weekend especially in the spring or fall Nashua can get very busy. There might be a few planes chasing each other around the pattern and numerous planes arriving and departing. When I was working on my Complex Endorsement in the rental Cessna 172RG we were number six in line leaving the run up pad and there was an arrival for practically every departure. All this time you are waiting in line to take off going nowhere the Hobbs meter is clicking over, $2/minute. Of course with ‘667 at the end of the day I still need to pay the gas bill but during ground operations a piston engine airplane is burning a lot less gas than in flight.

Since my Hobbs appears to be inoperative I could fix it. Hobbs meters aren’t particularly expensive – Aircraft Spruce has one similar to mine for $26. Right now it isn’t a necessity since as long as I write down the start time and stop time and do the clock math right I can get my hours from that for my logbook. Having a Hobbs meter would make that easier. So maybe some day I will replace the Hobbs meter but for now I am happy to be rid of it.