Expert: Ismar Avdic, Eng. - 8/1/2005

Question
Hi,

Reference Helicopter (preferably).

I would like to ask you a question on the recording of airframe hours. Can you please explain to me how a pilot accurately records flying hours:

Is there a device on board to accurately recording airframe hours?

Or,

Does the pilot simply make a note of the time when starting the engines and a note when shutting down? If this is the case, when does the recording take place; engine start, rotors turn, commence taxing or skids off?

I am trying to look at an accurate device to record these hours either electrically or mechanically to an Army aircraft!

Thanks for your time.

Christian Rouse

Answer
Hi Christian!
In USA General Aviation aircrafts are usually using HOBBS meter (FBO, aircraft renting places and so on..) However if you own your own airplane, mjority privately owned aircrafts do not have an HOBBS meter unless they have been used previously in clubs/FBO, and usually they do use engine TACH indicator to calculate airframe time, and owners also use it as logging time measuring device. Every airplane and helicopter is required by requlations 91.205 to have and engine indicator RPM and they are incorporated with engine TACH meter.
Now for military aircrafts I am not 100 percent sure, but I do suspecting that they are equiped in same aspect with an engine TACH meter and an HOBS meter for measuring flight time. HOBBS usually works on princip of engine oil pressure, so in other words as long as engine running it will indicate hours. While on big turbine airplanes HOBBS starts to measure time only after wheels leave  the ground, hobbs starts to tick.

Regards
Ismar