In a March 2025 poll commissioned by travel website The Points Guy, 65% of Americans surveyed indicated they’re more nervous about flying in light of recent incidents. In fact, 36% of those polled said that flying fears resulted in modified travel plans, like taking alternative transportation or canceling a journey altogether. Fresh events include a military helicopter colliding with an American Airlines jet in January, killing all 60 passengers; two of the airline’s jets clipping wings in a minor April collision on the ground at Reagan National Airport in Washington; and the tragic Air India Boeing 787 crash in June that killed at least 270, both inside the plane and on the ground.
The fact is, the odds of perishing in a plane crash are a staggeringly hopeful 1 in 11 million annually, according to PBS’s “Nova” series. You’re far more likely to be involved in a fatal car accident, which carries a 1 in 5,000 chance of occurring. Still, any unexpected noise from an aircraft, either on the ground or mid-air, is likely to set already jittery passengers on edge.
As it happens, most Airbus jets make a very strange noise indeed. One that sounds exactly like a dog barking. Assuming there aren’t any actual service dogs in the vicinity of your seat, that barking sound belongs to the aircraft’s Power Transfer Unit (PTU), a noisy hydraulic pump.
It’s all bark and no bite
The PTU’s function is to maintain a minimum pressure in the aircraft’s hydraulic systems. To hear one in action is perfectly normal and is more likely to occur on the ground, when taxiing to or from the boarding gate. It’s near the plane’s wings, so passengers seated close to them, like in exit rows, are more likely to hear its barking noise, which has also been compared to the sound of a power saw.
According to Airbus, the normal source of hydraulic pressure — which controls the aircraft’s slats, flaps, rudder, landing gear, and more — is the engine-driven pump. The PTU is a auxiliary source that activates when there’s a pressure difference of 500 pounds per square inch, or more, between those hydraulic circuits. Since the PTU tests itself when the engines are started and again upon landing, those are the two most likely times you’ll hear the barking noise, though it’s not totally unusual to hear it even after both engines are started.
Airbus’ single-aisle A320 jet and its shorter and longer variants like the A319 and A321 are immensely popular among both international and domestic carriers, including financially troubled Spirit Airlines. Ditto for the widebody A330, which has a successful record operating long-haul flights. As updated version of these jets are released, the PTU will eventually be discontinued. But for now, rest assured that the unique vocal stylings of the Airbus fleet are nothing to be afraid of.