When it comes to buying a PT6A powered aircraft there is no step more important that determining if the engine(s) are good. We do this in three ways, engine runs, oil samples and borescope inspection of the internal components.

Whenever possible I prefer to buy airplanes that have engines that are as far away from an engine event as possible. The only exception being buying an airplane that is close to overhaul and paying the "run-out" price for it. In this scenario you want to allow for the cost of worst case scenario overhauls and because the engine(s) are close, say within 600 hours you can usually get a pretty good idea of what that will be.

What most people do not realize is that there's a lot of stuff you cannot see with a borescope. There are areas of the engine that you simply can not access to inspect, today's technology allows those guys to do some pretty amazing stuff but just know that there are blind spots.

The big financial exposure during a hot section is the CT blades, there are several issues that can drive the replacement of CT blades.

One is cracks, the CT blades can develop hairline cracks near the base. If you have less than four cracks you replace the individual blades that are cracked. Four or more cracked blades... you have to replace them all. You might see them with a borescope and you might not.

The other is blade length, the disk of blades is measured when the engine is dissembled for hot section and those blades have to be a certain length to meet spec. Too short from blade rub or wear... you have to replace them all.

THIS CANNOT BE MEASURED OR DETECTED BY A BORESCOPE!

If you buy an airplane that is coming up on hots, you need to consider blade replacement cost and availability.

Adding to what Chip said, on the "small bore" PT6's you have to subject CT blades to a stretch check if they have more than 5000 hours time in service, and every 3000 hours after that. Some HSI's miss that. Also, if the engine was ever subjected to an inadvertent cut off and relight, then you have to sacrifice 2 blades and do destructive testing to see if they have damage to the crystal structure. If they do, then they all must be replaced. This is all spelled out in PWC SB's.

What is an inadvertent cut off and relight and how does it happen? Is that a flame out and inflight restart?

What is an inadvertent cut off and relight and how does it happen? Is that a flame out and inflight restart?

Inadvertent cutoff and relight is when you accidentally grab the fuel cutoff and pull it to cutoff, then realize you don't want to shut down the engine so you push it back forward again. It was happening so much on PC-12 (no idea why) that they designed a little latch that you have to unlock with your other hand to move the fuel lever to run. And yes, unless you have electronic trend monitoring it's on the honor system.

Do you have the specific PWC SB that calls for the stretch check? I am looking through logs of a -28 that just had a recent HSI, and I'd like to call that out since the other engine is due for a HSI soon, to see if it was done on the left engine, and make SURE it is done on the right engine if a HSI is performed

Yup, here you go.

Another comment on borescopes, especially in conjunction with a pre-purchase survey, be sure to hire someone who has a video borescope. Pictures or it didn't happen.

This not only gives you the buyer the reassurance that everything is good, it allows you to send photos to a third party to get a second opinion as well as provide a historical record of the condition of the engine.

I prefer to have one of the main engine shops do borescopes, that way if there is something that was missed that should have been caught you have someone to go back on that can actually do something about it.

I recently heard a story about an airplane that was purchased based on shop borescopes, it appears that they provided two borescope reports of one engine. He's a BT'er so I'll let him tell the story if he so desires.

Both the reports I've gotten (one shop and one big DOH facility) included photos and a pic of either the data plate or the tail number as part of the report. That's what you should be looking for, IMO.

I didn't ask, but I assume they had two data tags and then just loaded the wrong photos. This guys knows what he's doing, so it must have been wrong for him to have missed it.

And yes, you are correct, every report I have ever seen has the data plate as the first photo.