Hobbs Meter

The Hobbs Meter records the time a device is used. It is frequently used in aviation applications to record the time that the electrical power (battery master switch) is "on". Hobbs is a genericized trademark for products generically called "Engine Hour Meters". The meters run electrically, indicating hours and tenths of an hour, but there are several ways a meter may record the "Hobbs Time":

  1. It can measure the time that a master switch is on. This tends to overstate Hobbs Time.
  2. It can be activated by oil pressure running into a pressure switch, and therefore only runs while an engine is running. Many rental aircraft use this method to preclude flying with the master switch off to improperly reduce Hobbs Time.
  3. It can be activated by another switch, either an airspeed sensing vane under a wing (as in the Cessna Caravan) or a pressure switch attached to the landing gear (as in many twin engine planes). In these cases, the Hobbs Meter only measures the time the aircraft is actually flying. This is for those who wish to record Time In Service. Metrics such as Turbine Actual Runtime are kept to monitor overhaul cycles, and are usually used by commercial operators under Federal Aviation Regulations Parts 135, 121, or 125.
  4. It can be activated when the engine alternators are online (as in the Cirrus SR series).

Read more about Hobbs Meter:  General Aviation Use

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