Aero-Tips!
A good pilot is always learning -- how many times have you heard
this old standard throughout your flying career? There is no truer
statement in all of flying (well, with the possible exception of
"there are no old, bold pilots.")
Aero-News has called upon the expertise of Thomas P. Turner,
master CFI and all-around-good-guy, to bring our readers -- and us
-- daily tips to improve our skills as aviators. Some of them, you
may have heard before... but for each of us, there will also be
something we might never have considered before, or something that
didn't "stick" the way it should have the first time we memorized
it for the practical test.
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Aero-Tips 12.12.06
Logbooks. Rental fees. Inspections. Overhauls. Taxes. There are
a number of elements of flying and operating aircraft that are
dependant on aircraft time. Rules, regulations and suggestions tell
us to base most everything on the amount of time the aircraft has
run... but there's nothing in the "regs" that says how to judge
that time.
There are three "types" of aircraft time. Each has advantages;
under Federal Regulations we can choose the type of time that best
suits us.
Hobbs time. A Hobbs meter (a trade name) is a
digital counter that records sequentially how long an airplane has
been operating. Hobbs meters measure time accurately when full
electrical voltage is available.
- In most fixed-gear airplanes the Hobbs meter is wired to the
battery master switch. Even if the engine isn't running, the Hobbs
is recording actual clock time as long as power is applied.
- In many retractable-gear airplanes the Hobbs meter is wired
through landing gear squat switches. It records time only while the
airplane is airborne.
- In some unusual situations a Hobbs meter might be wired to
sense other things, for instances, when the engine oil pressure is
above a certain limit. A Hobbs wired this way would measure actual
clock time when the engine is running.
Hobbs meters are generally used for airplane rental time, and
often for time that's put in the pilot's logbook. If flying a
retractable-gear airplane with the Hobbs wired through the gear
system, this would cheat you of civilian-loggable time during
ground operations, although it would save you money on airplane
rental.
Tach time. Most propeller engine tachometers
have an "odometer"-type recording capability with time displayed on
the face of the instrument. Tach time is usually set to be accurate
clock time when the propeller speed is above some point, for
instance 2250 rpm. Since tach time records slower when the engine
is running slower, it's not usually used for rental time or time in
a pilot's logbook. But because tach times often does not build as
rapidly as Hobbs time, it's to an owner's advantage to use tach
time for judging time between 100-hours inspections (for
commercially used aircraft), repetitive Airworthiness Directives
and engine overhaul.
Actual clock time. Since the regs don't tell us
how we're supposed to measure time, we can also use actual clock
time. Record engine start and engine stop times, and use these to
your advantage. Since there is no permanent record in the airplane,
and because it will usually record more time than either a Hobbs
meter or a tachometer, it's not convenient to use actual clock time
for aircraft inspection intervals or tax purposes. It is
advantageous, however, to use actual clock time for time in your
pilot's logbook, if your goal is to log as much time as legally
possible.
Be consistent. Use whatever time best serves
your needs. But be consistent. Especially is you're recording
aircraft time for some tax purpose, but also to satisfy the FAA if
ever arises a question of pilot time, airplane inspection or AD
intervals, use the same type of time for each type of log
entry.
Aero-tip of the day: Know the "types" of
aircraft time, and use each type appropriately to your
advantage.