Yesterday I touched on safety when speaking about the recent Egypt Air crash. Safety is a big deal in the aviation industry and everyone goes through a lot of effort to make it that way. As engineers, we always had to account for things going wrong that you may not have ever considered. I want to take a look at those items in an effort to show just how much work engineers in the aviation industry put into working around potential midair problems.
Lets take a look at some scenarios and how the aircraft is made safe in those cases:
Case One - Engine Rotor Burst
There is an unlikely case where a fan blade in the engine might come loose. This is called a rotor burst. Should a fan blade release from its mounting, the fan often becomes unstable from the failure and tears itself apart. Worth noting here is just how rare this is. To give you a statistic that may be a bit old at this point, but when the 787 was built, GE had been using carbon fiber fan blades on the 777 for over 10 years. In that time, only two fan blades had ever been replaced... key word, ever. The GE90 engine was incredibly powerful and over it's 10+ year lifespan at that time, it had only ever had 2 replacement blades used on all of the engines in flight around the world.
However, we plan for the worst. GE, Rolls Royce and Pratt and Whitney are some of the largest engine manufacturers int eh world. Each of them is required to contain a rotor burst in the event that it does happen. Every engine is tested at full power, then a small charge breaks the fan loose and destroys the engine. This test must show that none of the engine parts are released from the engine enclosure. This is engineering safety level one, contain the failure. Every engine must pass this test before certification
Secondarily, on the wiring side of the equation, something I am very well versed in, we take another step. While wiring a plane, we separate control wiring and backup control wiring into different zones. Every wiring zone carries different cabling for control, and flight control wiring must be kept a certain distance away from any redundant system wiring. In the event that a rotor burst escapes from the engine and hits the fuselage of the aircraft, we segregate backup wiring so that if one is cut from the burst, then the other backup channel is far enough away that it is unlikely that both would be cut by the rotor burst.
This is a huge level of effort that is just for a single event, and we plan for many, many cases.
Case Two - Loss Of Power
Have you ever been curious as to how an airplane would continue to fly if the engines lost power and electricity stopped flowing to vital controls. With new fly by wire systems such as the 787 has, these aircraft rely heavily on electrical power, but what happens of the engines stopped producing power, or shut down all together.
We've got a backup for that, it's called the Auxiliary Power Unit or the APU. The APU is not just a backup unit, it also provides power on the ground if there is no external power at the airport that does not provide such a service. The APU is essentially a mini jet engine that is not there to push the plane through the air, but rather to generate power for those situations where power is unavailable or in the event of an in air emergency.
What happens though, if the engines fail, and the APU fails? Don't worry, we've got a backup for the backup. This unit is called the Ram Air Turbine, or RAT. This is truly an emergency only device. The RAT is gravity dropped beneath the aircraft and looks like a tiny propeller. While power from the RAT is not enough to run the entire plane on, it is enough to power vital systems like the controls, radio, and in flight displays.
So the next time you hear about how unsafe airplanes are, just keep in mind how much effort we as engineers go through, to keep you safe... if cars had the level of safety planes do, it might be a very different world.