Keeping jet engines healthy

Aircraft are complex machines that fly tens of millions of miles over their lifetimes. But what does it take to keep an airliner running smoothly, and how can you tell when or if it's in need of a service? The key components of any aircraft are its engines. And the world leader in this sector is UK-based Rolls-Royce. They make about half of the world's jet engines. But rather than selling their engines, they retain ownership of them and effectively rent them to aeroplane owners. This means that Rolls-Royce take responsibility for monitoring and maintaining them. Philip Garsed went to Rolls-Royce HQ, in Derby, to speak to Nick Ward, and before him Matt Burns who heads the company's Operational Service Desk...

Matt - We're here in our customer training centre. We're stood in between a pair of Trent XWB engines. These are engines that power the airbus A350 aircraft that successfully entered service in October of last year with Qatar Airways.

Philip - This thing is absolutely massive. At the front of it, there is a fan that is much bigger than I am tall. It's made of many enormous fan blades. It will take me 10 paces to walk down its length and it's covered with pipes and wires. It's just an incredible piece of engineering to look at and it completely dwarfs me.

Matt - They're pretty impressive beasts when you get up-close and of course, we're seeing it here stripped of its outer cowling. So, it isn't the glossy, painted exterior that the traveling public may be used to seeing, but it's nonetheless impressive.

Philip - Can you explain to me how an engine like this actually works?

Matt - So the engine, as you can see at the front there, is really dominated by this large fan. Eighty per cent of the thrust of the engine is generated by that fan. You might consider that the engine is almost pulling itself through the sky, sucking tremendous volumes of air through itself and pushing them out in the back, roughly, the equivalent of a squash-court-full of air is being pulled through that engine every second.

Philip - It's not just its huge fan blade on the front though. I can see that it gets a bit smaller in the middle and then there's lots of other smaller blades inside. What are they doing?

Matt - The rest of the engine is to generate the power that's needed to propel that fan at the front. The air is being pulled into the front of the engine and packed down tighter and tighter and tighter, and then we're going to add some fuel and light a match! So, that really tightly compressed, energy-rich air is filled with even more energy from the fuel and from the ignition, and that energy is then released as that air rushes out through the turbines of the back of the engine.

Philip - How hot does it get in the middle of this thing?

Matt - The turbine blades in the high pressure system in this engine, they're sitting and working in an environment that's actually beyond the melting point of their raw material. Whilst at the same time, being subject to forces that are about equivalent to hanging a double-decker bus off the end of each individual one of them!

Philip - How do you keep a machine like this working optimally for its entire lifetime?

Matt - It's just a given that this will deliver that tremendous amount of thrust reliably every time that's required of it. We're talking about each engine accumulating 40 million kilometres of distance-travelled before it's removed from the aircraft for overhaul. Our ability to do that is really supported by the data and the information which we can extract from these engines whilst they're operating.

Philip - And when Matt talked about extracting data whilst the engines are operating, he quite literally means whilst they're flying you on holiday. On the side of the engine is a small grey box that collects information from sensors all over it and that box beams this information back to the nerve-centre at Rolls-Royce in Derby...

Nick - Hi. I'm Nick Ward. I'm the product manager for equipment health monitoring - that's to do monitoring of the engines. We have 12,000 engines actually coming in to our global data centre. We're looking at the temperatures, the operation, the speeds of the shafts, the pressure drops between different stages. All of that data is then coming through to us as individual parameters measuring each flight. That then goes into a system where we're looking at what does it all mean and other things of interest we want to see in the data. And then we alert people like Matt in the operation centre to take some action.

Philip - Why do you need to collect so much data?

Nick - If you want to look at this from the airline's point of view, they want to concentrate on putting passengers on aircraft, putting pilots on aircraft and flying. That's how they make money. They would like to give the responsibility of looking after the complicated engineering elements to somebody else.

Philip - You're letting the airlines get on with the job that they do best, which is shifting people around, and you're getting on with the job that you do best, which is making world-leading engines?

Nick - Exactly.

Philip - If you notice some data points which aren't quite what you'd hope for in mid-flight, what do you do then?

Nick - We look to see whether there were any spikes in any of those parameters, anything which might be moving upwards or moving downwards unexpectedly. We call those things features inside the data. We collect a number of those features together and they might represent a symptom. A number of those symptoms will then form a diagnosis, very much the same as you go to a GP. You're taking the temperature of the engine, you're looking to see whether the temperature is going up. When I'm hot and sweaty then maybe my diagnosis is that this is the 'flu. It's very similar on an engine. The diagnosis is then passed on to the operation centre here, and Matt will take that information, which then leads us to make a decision. Is it something that we want to take action on? Should we schedule an inspection? Maybe send a camera down inside and see whether we can get a bit more information.

Philip - Send a camera down inside the engine? That sounded intriguing, so I spoke to Matt back at the engine to find out more...

Matt - A simple way to think about this is actually to relate it to some of the medical practices which are pretty common place now. So, if a doctor decides that he wants to take a look inside you, he doesn't come straight in with a knife and open you up. A more common approach these days would be to introduce a camera, an endoscope. So, in our industry, we refer to these as borescopes. If you look right underneath the engine here, you can see some of these ports here. So, where we've potentially seen something in the data that might warrant us to take a look in the engine and check how everything is going; we'd be able to remove one of these ports and introduce a camera deep into the insides of the engine and actually see what's going on. If we were to find some damage from something that had been sucked in through that tremendously powerful fan at the front, we've got the ability to take positive action to remove that damage, possibly with the use of laser techniques or more traditional mechanical techniques, so that we can get the engine back to its full health and deliver reliable performance for the life of the engine.

Chris - Philip Garsed speaking with Matt Burns and earlier, Nick Ward. They're both from Rolls-Royce. Sounds like you had a fascinating time and an endoscopy for an engine. I couldn't resist the medical analogy.

Philip - Yes, it's absolutely amazing that some of technology that people use to look inside people in medical settings are actually also used in a very similar way in engineering. The thing that really struck me about the whole place was just the sheer scale of it, how it was necessary to bring in data from across the world. And I walked into this control room where there was a screen with the map of the world and data about engines and planes, all in flight. Teams and teams of people, all keeping an eye on the data, just to make sure that everything was ticking along nicely.

Chris - Did they actually run the engine with the camera in there, or is it a question of if you thread the camera in then you just turn the engine over to inspect the components?

Philip - The camera is there if they decide they want to have a bit of a closer look because these things are so complicated that actually taking off the wing and taking it to pieces is a really big ask. And so, these are just used when they've seen something in their data and they just want to have a quick look and check that everything is okay, and maybe decide if anything more substantial is required.