Expert: Marc Ebelini - 9/24/2005

Question
 
Hi,

My name is Christian Rouse, and I work within the British MOD and I am trying to research a method to accurately record airframe hours. Currently the pilots just look at their wrist watch (when they feel appropriate) and then record the time when they arrive back from their sortie. This, as you can appreciate is generating unnecessary maintenance and hence increased costs!

The aircraft has a wheeled undercarriage and two engines and an APU. Can you recommend a system, and where would you embed the system; undercarriage, main rotors, engine start or when the electrical system is switched on?

Your time is much appreciated.

Thank you very much.

Regards

Answer
Mr. Rouse:
Recording airframe hours can be accomplished in many ways. Originally, there was two ways that comes to mind; one was tied to the  oil pressure switch so that when the engine was started the clock  would also start. Obviously while that recorded engine time it was a poor indication of airframe time since the engines are run for maintenance without flying. The second method was the tachometer time, where the tachometer had a clock that was operated by the engine RPM. That too would give engine and not necessarily flight time because the clock time was based relative to the engine RPM at the normal cruise operation.
The best method to tell the actual time in the air is with a vane switch because this will tell you the actual time the aircraft is airborne. In a single engine propeller aircraft, it must be placed out on the wing away from the prop wash. Jets or multi engine aircraft it can be mounted up close the nose. I am not longer actively engaged in business but I did installed many of these clocks. There was a company in Redwood City California that made one that would allow accumulated time or allow you to reset it after every flight. The digital clock also worked as a count down timer for timing instrument approaches as well as indicating real time. The six digit display would allow the pilot to select which clock he wanted to view. Hope this response answers your question. You can use any electric clock that runs on the aircrafts voltage. Vane switches can usually be found at aircraft supply company.