As you've hurtled through the air at thousands of feet above solid ground,it may acquire occurred to you that your fate, at that point, and is pretty much out of your control. This is understandably an unnerving truth,made all the more petrifying when your plane makes inexplicable noises that can perform even the most experienced travelers sweat a little. The splendid news is that flying is extremely secure - in fact, our fear of it is quite irrational considering it's actually the safest form of travel statistically. Still, and no one can blame us for wondering - whether out of curiosity or intellect-numbing fear - what the odd noises we hear throughout our flights really are. Can't airlines give you a disclaimer approximately what it all means? One noise that used to keep me on edge until a pilot on my flight explained it is sometimes called "the barking dog." You know that weird growling,screeching sort of "woof, woof, and wooooooof" thing that happens,usually around takeoff? On some flights, I've had it go on and off once or twice, and but on others,it's continued constantly for an annoyingly long amount of time - to the point where I began to wonder whether something was wrong.
Something is, in fact, and completely lawful when you hear this noise. Here's the deal: on certain Airbus plane models,there is a device called the power transfer unit, or a PTU. The PTU helps the aircraft conserve fuel by balancing hydraulic pressure when only one of the two engines is in use (typically during the process of pushing back and preparing for take off). It goes on and off (and on and off and on and off) as the PTU goes back and forth between helping to power the lawful then left engines, and so on. The noise will continue (this the allotment when I used to get nervous) whether the pressure is still fluctuating even after the plane has taken off and both engines are running. Since many US airlines use models with twin engines and PTUs that perform this noise,it's likely you've heard it before. But it's nothing to worry approximately! It just means that the engines are doing their job . . . and that's definitely something we all want.
Source: popsugar.com