Speaking of current topic in the news. Jet engine vs. birds

[benhasajeep]

Since it has been a big topic in the news lately here is an engine that has had some damage, most likely from birds. One thing that might amaze you is alot of this damage is allowable!!

Here are some captures I took tonight while boroscoping an engine comming off one of our 757's. The engine is a Rolls Royce RB211-535. No comments on picture quality or focus or any of that stuff. These are still captures from a 7mm fiber optic video boroscope. My little $50,000 work toy, er I mean tool.

This is the front of the engine. The ring of blades closest to the white area in top right, is where the air goes inside the engine. From that middle ring (arcing down from top middle, to right middle)is the dividing point from air that goes inside the motor. And the air that bypasses the internal areas of the motor. The air that bypasses is just air that is accelerated by the big fan.

This is a third stage Intermediate Compressor blade. Compressor section does exactially what its name implies. It compresses the incomming air. This is a picture of a good blade.

This is a bad blade.

Little different type of damage. Notice the streak comming from it.

Now were getting down right mad.

Couple of twins want in on the act.

This motor is being changed tomorrow.

 

[fiveoboy01]

Cool.

How often to you have to scope the engine? I assume there is some sort of schedule for that...

 

[benhasajeep]

Even though its not required my company boroscopes each motor every other maintenance check. A maintenance check is done about every 450 flight hours. So we check our engines about every 900 hours of flight time. Sometimes we have to check even more frequently if we know something is within limits but maintenance manual or just my company wants to look at it more often.

 

[Wildlife girl]

This is interesting.

You know I was talking about the accident with my parents, and my mom was wondering why it isn't possible to put some kind of screen on the engine so that birds can't fly in?

Obviously I know there is a reason, or they would have done it! So, I figured you were a good one to ask.

Thanks!

 

[kn4ds]

This is interesting.

You know I was talking about the accident with my parents, and my mom was wondering why it isn't possible to put some kind of screen on the engine so that birds can't fly in?

Obviously I know there is a reason, or they would have done it! So, I figured you were a good one to ask.

Thanks!

Just off the top of my head...

If there were such a screen, and there were a bird strike, the screen could get clogged enough so that the air flow were choked... with the same result... a non-functional engine.

 

[bradsperry]

we install inlet barrier filters on military aircraft. the only problem is it reduces the torque that the turbine is able to produce, in turn reduced performance. i haven't heard of civil aviation or commercial aviation using any but that doesn't mean they don't in certain applications.

 

[benhasajeep]

The problem with screens in the front is to make them strong enough they would block too much air. At 200 miles per hour even a little sparrow can cause damage to a screen. Most items actually get slung to the outside and go through the bypass area. And you only need to dress the fan blades (the big ones in front). If you get bad enough damage, you can change a fan blade in a couple hours. They are changed in pairs. The one thats damaged. And its pair 180 degree opposite. They have to weigh very closely to each other to maintain balance.

The engines can take alot of damage. Single birds rarely cause problems. But I would bet the US Air plane hit a flock of geese. Thats just more than an engine or in this case engines can take.

Some helicopters have inlet screens but they are meant for small debris, and are not subjected to items hitting at very fast speeds. It all has to do with mass and accelleration and all that math stuff. The GE90-115 engine on 777-300's are over 10' across the inlet. Imagine how heavy and strong a screen for that would have to be.

 

[Wildlife girl]

Thanks for the answers! It's kind of what I was expecting to hear, though I didn't know the details.

I believe too that it was a flock of geese. The Co-Pilot had said he had seen a flock of birds flying in perfect formation shortly before the impact to the engines. Well, that's gotta be geese.

But, I guess we'll have a better idea after the plane is examined.