Contamination In The Gearbox

One of our helicopters (PK-HCR) was due for a routine inspection. This includes removing the main gearbox’s oil filter, then inspecting, cleaning and reinstalling it. Unfortunately, during the inspection phase I found contamination in the filter that was very concerning. The main gear box has many moving parts (bearings and gears) that require a steady flow of oil to lubricate them. The size of the particles could easily plug one of the lubrication jets, so we had to look deeper to know the extent of the contamination. Every flight our helicopters make is over very unforgiving terrain where there is no opportunity for an emergency landing. So, the lack of lubrication could have catastrophic consequences. 

We started by draining all the oil and checking the gear flanks with a boroscope. (A boroscope is a tiny camera with a light source that we can feed into the transmission through an opening and look for possible damage). Finally, we disassembled the entire gearbox to find the cause of the contamination. After a thorough inspection of all the gears and bearings, we could not find any damage. The contamination must have entered the gearbox from the outside. Whatever the contamination was, it was all caught inside the filter, which had done its job in protecting the gearbox from contamination. So we reassembled the whole gearbox with new seals.  

Matt, Mechanic

Matt with warriors

Installation of transmission

Epicyclic and mast

Particles we found