March 18, 2013

HSI's and other 3 Letter Acronyms

Aviation is full of acronyms. In fact, when it comes to HSI, it could mean either Horizontal Situation Indicator or Hot Section Inspection. And let's not even get into pilot talk, as that could qualify for another linguistic dialect altogether.

A Hot Section Inspection is when you take apart a turbine engine (in our case, a PT6A turbo-prop engine) and, well, inspection all the parts that get really really hot, and spin really really fast.

Earlier this year, a Hot Section Inspection was just what we did on our Kodiak MEB. It is actually the highest time Kodiak in the world, so this is the first time ever a HSI has been carried out on a Kodiak in the field. (MEB, by the way, is not an acronym but part of the aircraft's registration. The funny thing is, pilots & Air Traffic Control folk normally expand these registrations as call signs for purposes of clarity over the radio, ie: "Mike Echo Bravo".)

Below is MEB with the front 1/2 of it's engine missing. One of the main purposes of the back section of engine (still shown on the airplane) is to basically provide large amounts of compressed air, that will in turn be mixed with fuel and burnt like a big torch, hence the "hot" section.
Almost 2/3's of the engine's produced horsepower is used to make this part work - more than is used to turn the propeller! I still find that kind of weird. The next time you are in an airplane and feel all that fresh air blowing through those little vents above your head, you can thank this part of the engine. That's why when the engine's are starting, the air turns off in the cabin for a few minutes while the engines get up to speed & the pilots turn on the environmental system. I love watching every one fiddle with their air vents wondering if they broke. I think I've even done it myself.
 Above, Karl & Tim have fun figuring out what parts of the temperature probe system needs replacement.
Hot section components! These parts are worth a lot of dollar bills, and are pretty critical to a happy turbine engine. The compressor turbine (shown below) spins around 33,000rpm at very hot temperatures. Every so often, we replace a lot of these critical components and send the used parts back to the US for further inspection, replacement, or repair.

Although the component costs associated with these engines are rather huge, the amount of people and cargo these planes are able to carry make it worth while. Smaller, older, & cheaper airplanes are not necessarily that much more cost effective.

The front section of the engine & propeller hanging on the hoist waiting to be installed.
Reg making sure all is well! Or maybe he's looking for that wrench he forgot the last time he was in here (joke). We promise you, there weren't that many extra parts left over when we figured out how to put it back together.

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