Airbus has enjoyed a successful period in the market recently, and the A320 and A330 have become extremely popular in the airline industry. But these jetliners do feature one intriguing quirk. Passengers on the A320 and A330 can expect to hear a barking noise emanating from the plane at some point during their flight! So what is the cause of this unusual barking dog sound?
The barking noise, which has also been likened to a buzzsaw, is actually caused by a hydraulic pump which is referred to as the Power Transfer Unit, or PTU. The location of the PTU means that the barking dog sound is most likely to be audible for those seated in proximity to the wings of the aircraft, but it is loud enough that often others in less adjacent seats can also hear it as well.
Unusually for a pump system, most of which are powered electrically, the PTU is hydraulically powered. The purpose of the system is to ensure that minimum pressure is maintained across the hydraulic systems of the aircraft. This system produces the ‘barking dog’ noise that is associated with the Airbus series, which also sometimes manifests itself as a high-pitched whining noise.
Not only can this noise be slightly irritating for those on board, but some passengers have been alarmed by this confusing sound. Because the noise comes intermittently – starting then fading and then reappearing again – some passengers may feel concerned, believing it to be an engine cutting out.
The barking dog sound is actually nothing to do with any problems with the engines. The reason that the noise comes and goes is that the PTU is only operational when the hydraulic pressure of the A320 or A330 drops below a pre-defined level. And due to the fact that pressure can fluctuate, the noise will sometimes continue even after both engines are fully operational.
Another reason that the PTU may be running is that the system tests itself when the starboard engine of the plane is initially fired up, and this process is repeated shortly after landing. Interestingly, some Boeing aircraft also feature a PTU unit, but it doesn’t operate in the same way as the one employed on Airbus aircraft. For that reason, it doesn’t cause the same barking dog phenomenon.
Airbus aircraft do emit some strange noises in general. Another one that has been picked up by many passengers is a shrill whining noise, which can be heard at the gate prior to departure and again after landing. This sound can be explained by an electric hydraulic pump on board the aircraft, which is used in the process of opening and closing cargo doors.
Have you heard the ‘barking dog’ on an Airbus? Did you know what it was all about?