An expert explains that strange "barking dog sound" before a plane takes off, and gives us one less thing to worry about the next time we fly
What Is the “Barking Dog Sound” on a Plane Before Takeoff?
Published on Mar. 14, 2025
Due to several recent air disasters and a few near misses, changes in government agencies overseeing air safety, and generally heightened anxiety over global events, travelers are justifiably feeling a bit more anxious about taking to the skies. And while air travel remains fundamentally safe, in stressful times it’s hard not to worry at least a little, especially as your plane takes off. An odd sound, an unexpected movement of the plane—should these be causes for alarm? Fortunately, we can help get to the bottom of one airplane curiosity: that strange sound you hear before a plane takes off.
Since airline industry professionals presumably don’t call it the “barking dog sound” like the rest of us do, we asked Kristy Kiernan, PhD, an associate professor of aviation at Embry‑Riddle Aeronautical University, to explain the curious sound to us in lay terms. But fair warning—even a “simple” explanation is fairly complicated. Read on to find out the details and get to the bottom of this airplane mystery.
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What is the barking dog sound?
Some people think it sounds like a barking dog. Others say it’s a knocking sound. I’ve always likened it to someone grinding or sawing something metallic, or maybe to someone pumping a really noisy set of brakes. It seems to emanate from the cargo hold, as a plane gets ready to leave the gate, or when it’s taxiing to the runway for takeoff. Most of us have gotten used to it, but it’s still a loud, odd noise to hear coming from the bottom of the aircraft, especially right before takeoff, which is among the most dangerous phases of a flight.
What is hydraulic power?
Before we get into what causes the sound, you’ll need to understand hydraulic power. Now, here’s where it gets technical. “Airliners use hydraulic systems to power a lot of systems—for example, the flaps which you will see moving down on the back of the wing on landing, and retracting back after takeoff, or the slats which extend from the front of the wing for takeoff and landing,” says Kiernan. “These features extend to allow the airplane to fly more slowly during takeoff and landing, but retract to allow the airplane to function efficiently at higher speeds during cruise flight.
“Hydraulic power involves using a pressurized fluid to transmit a lot of mechanical energy through small pipes,” she continues. “Airplanes that use hydraulic systems will have a hydraulic pump that pressurizes hydraulic fluid to usually around 3,000 pounds per square inch. The pump pushes the pressurized fluid to the actuator, which makes the flaps, slats or landing gear move.” (So if you thought that funny noise sounded like a pump, you were dead-on.)
Because these systems are so crucial to airline safety, manufacturers install what Kiernan calls “redundant systems.” For example, the A320 family of airplanes (more on this below) has two engine-driven pumps that power two independent hydraulic systems, plus a third electrically driven pump in the event that hydraulic pressure drops.
What causes the barking dog sound?
“Since the pumps are engine driven, when the aircraft is operating on one engine, the third electrically driven pump will operate to equalize the pressure in the two independent hydraulic systems,” says Kiernan. And that, folks, is what makes the “barking dog sound.”
“You will hear the noise whenever there is a differential pressure in the hydraulic systems, usually if the aircraft is starting up an engine or operating on one engine,” says Kiernan. She explains that aircraft sometimes taxi on just one engine and start the second engine closer to the runway. “So you will hear the noise at the gate, but also you can hear it during taxi,” she adds.
On what type of aircraft are you likely to hear the barking dog sound?
You’ll only hear the sound if you’re flying on an Airbus A320 family of aircraft, which includes A318, A319, A320 and A321 planes, Kiernan explains. Currently, about 60% of all commercial planes are Airbus, with A320 and its siblings making up the majority of that working fleet—so chances are pretty good that you’ve flown on one at least once.
Is the noise ever a cause for concern?
The short answer is no. Although the noise is associated with takeoff, even if you hear it mid-flight, it’s not cause for concern. Kiernan says it’s “simply evidence that the airplanes redundant systems are functioning as intended.”
Because other aircraft, including different Airbus models and those of the other industry giant, Boeing, have different systems, only the Airbus A320 planes make this distinctive sound. “It is completely normal and not a cause for concern at all,” says Kiernan. If you only hear it sometimes, it’s just because you don’t always fly on an A320 airplane.
So … mystery solved! While I still like to imagine a member of the ground crew poking around under the plane with a big wrench, it’s a far less manual procedure than that. And there are no dogs—barking or otherwise—involved.
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Sources:
- Kristy Kiernan, PhD, an associate professor in the Worldwide College of Aviation and the Boeing Center for Aviation, and Aerospace Safety associate director at Embry‑Riddle Aeronautical University; email interview, March 2025
- Michigan Journal of Economics: “COMAC’s Impact on the Future of the Airbus-Boeing Duopoly”
- Simple Flying: “Why There Will Soon Be More Airbus A320s Flying Than Boeing 737s”
