Hobbs Meter - General Aviation Use

General Aviation Use

For general aviation, Hobbs Time is usually recorded in the pilot's log book, and many Fixed-Base Operations that rent airplanes charge an hourly rate based on Hobbs Time. Tach Time is recorded in the engine's log books and is used, for example, determining when the oil should be changed and the time between overhauls. Tach (tachometer) time differs from Hobbs Time in that it is linked to engine revolutions per minute (RPM). Tach Time records the time at some specific RPM. It is most accurate at cruise RPM, and least accurate while taxiing or stationary with the engine running. At these times, the clock runs slower. Depending on the type of flight, Tach Time can be 10–20% less than Hobbs Time. Many organizations such as flying clubs charge by Tach Time so as to differentiate themselves from Fixed-Base Operations by the fact that 10-20% less time recorded makes it 10-20% cheaper to fly (if the hourly rate is the same).