What’s up asked:


can’t the blades slice the birds into millions of tiny pieces before they even pass through
how do they break the fans. how thick are these fans. ain’t they suppose to be thick
IAN

8 Responses to “How can a few birds bring down some planes?”

1. Fly B on December 21st, 2009 5:35 am

   Well, government regulations make the engine manufacturers prove that the engines can handle birdstrikes. They fire birds into running engines to prove the engines can take it.

   How these birds brought down the plane, they must have been big, it must have been a flock, and there may yet be extenuating circumstances that the investigation will reveal later.

2. rachel f on December 23rd, 2009 2:20 am

   well they flew into the propellers but my guess was that there were so many that it just kinda stopped it up as funny as that sounds.

3. tomcotexas on December 25th, 2009 1:29 am

   The birds cause the fins to break, which breaks more fins, and that is what destroys the engine. A tiny bird might not break a fin, but a larger one will, and you only need break one fin to start the destruction.

   Tomcotexas.

4. Tj C on December 26th, 2009 7:54 pm

   A flock of them clog the engines and choke the engines

5. jayme on December 29th, 2009 4:05 am

   they are saying it was a FLOCK of birds, and it only takes a few birds to take out an engine. Last I heard they were saying there were geese, I don’t know how reliable that is though.

6. Larry454 on December 30th, 2009 2:09 pm

   Bird strike is one of the more challenging tests to perform in the engine certification process. The bird enters the inlet going about 200 mph, but the fan blade tips may be supersonic, so the bird actually hits the fan at about Mach 1 - relative to the fan blade. Depending on the mass of the bird and the thickness of the blade, this can do a lot of damage. It is not unusual for fan blades to bend almost double when they strike the bird. I have seen slow motion films of bird strike tests where the titanium blades look like strips of rubber waving with the impact. Sometimes, one blade will move so far that it will hit another blade and both will be damaged. If a fan blade is lost, it can cause a lot more damage (although it must be contained by the inlet case per the FARs).

   The certification requirements do not address multiple bird ingestions. They do account for larger and smaller birds, but not flocks of them. Frankly, a whole flock of birds ingested into both engines is considered sufficiently rare that it is not in the spec (if it was, fans would be a lot heavier and planes would be much less fuel efficient).

   The eternal question for engineers and the FAA is - “Where do we draw the line? How safe is safe enough?” There have been aircraft that have hit deer on the runway on takeoff roll. We do not design nor test for deer strike. You cannot possibly cover all the possibilities, but we do the best we can.

   ADDED: I agree with my friend below. A flock of sparrows will not even make most engines sneeze (very small engines, perhaps). But a flock of geese - that is a different matter. I’m not even sure the blades would fail in fatigue. It would probably just be a massive overload on several of them. If it was fatigue, it would be very low cycle fatigue - like two or three cycles.

7. richard b on December 31st, 2009 6:59 am

   larry454 said it all. one bird may not destroy an engine, but several will. each time the fan blades are struck, or even through normal use, they are subject to fatigue. if there are any stress risers anywhere along the fan blade, it will ***** under the stress, and break. when that happens the damage compounds itself as more blades are broken. as each blade breaks the engines also lose their balance, and the ensuing wobble under power will cause even more damage to occur. all this happens quite quickly, especially when under full power as those engines likely would have been during takeoff and climb out, thus the pilot needs to be on top of everything going on at that instant to prevent total disaster, and in this case he was.

8. Techwing on January 1st, 2010 10:42 pm

   The birds that cause trouble are large, weighing several pounds and with large wingspans, usually. The engine does indeed dice them up and cook them, but the sudden impact of even the small weight of a bird at high speed can damage and/or destabilize a jet engine, particularly one that is running at near full power for take-off. The air flow through the aircraft is disrupted and this can damage the engine in itself, or cause a serious loss of power.

   Fan blades are incredibly strong, but the impact of a bird at high speeds isn’t much different from shooting bullets into the engine in terms of energy delivery.

   Smaller birds just go right through the engine without ever causing a hiccup.