East ás in a grandfatherón and suddenly a sound like a dog barking or a screeching sound starts when the engines start, ¿a qué must be?
Post written by: Capturesán Rodolfo Estrella
Twitter: @rodo_estrella
Many times when we have flown in an airplaneón of the family Airbus A320, We have heard that when you start your engines a very loud sound appears that seems to be the barking of a little dog that isá at the bottom of the planeón, This sound comes from a hydraulic power transfer pump.áulica of the ancestorsón (PTU Power Transfer Unit).
«The dog that barks»
To understand the barking sound we must first know a little about the hydraulic system.ádel avi streetón al what isá related, becauseé sounds and in whaté conditions you can hear the pump working.
The airplanes Airbus A320 series have three hydraulic systemsáseparate and independent cells that power the systems that require actuationóin hydráulica of the ancestorsón, for example control surfaces, undercarriage, spoilers, among others. These three systems are differentiated by the manufacturer as a green system, yellow system and blue system.
the green system (left side of the planeón) It is powered by a hydraulic pumpáulica acted by him motor número 1, and the yellow system (right side of the planeón) by the hydraulic pumpáengine numberúmero 2 and additionally has a hydraulic pumpáulica theébackup power and a manual pump to operate loading doors from the outside.
If never oríthis this sound, we share it hereí:
The blue system is activated újust for a bombéelectrical or in an emergency by an emergency air impact generator or RAT, this system is notá associated with “barking dog”
Now that we are clear about the three hydraulic systemsáindependent ulics approachémonkeys in green and yellow. These systems normally operate with a pressureóin hydrástreet de 3000 PSI that must be the same for both systems.
If you were takenón durante su operationón for any reason or for a péengine loss, decreases 500 PSI, go into actionón the PTU pump which, as we mentioned, is a hydraulic pumpáulica located between the two systems and that actsúa to equalize the pressureón of both systems the replacement of presidentón to the system in failure by péengine loss and keep both in 3000 PSI, using pressureón of the system that isá normal to equalize the pressureón of the system with baja takenón.
It is very important to mention that this pump, although it uses pressureóin hydráulica of each system to equalize them in pressureón, PTU does not mix hydraulic fluidsáulic or transfer fluid from one system to the other. That is why, if the failure comes from a péhydraulic fluid speedáulico on one of the systems, the PTU pump must not be activated and the hydraulic system must be declaredáulic with péfluid loss as lost.
When the avión isá on the ground with their engines off, the systems have no pressureóin hydrástreet, but when you start the engine 1, the green system gets the 3000 PSI de operationón normal, BUT the yellow system associated with the second engine has no pressureón, since this is a conditionón in which the OCT mustíto come into operation to equalize the pressureón between the two systems, BUT it is in the ignition stage, it enters a SELF TEST stage where it starts to work as long as inhibiting conditions for the PTU are met, such as the parking brake being on.é activated. It is because of this situationón that the “barking dog” usually orírse con más ground clarity during aircraft ignitionón.
When both engines have started and both systems reach their pressureónormal number of 3000 PSI, the pump stops working and the sound ends. Nevertheless, the operationón of the avión normal requires hydro poweráulica for your different systems and this pressureón often fluctuates so the system comes into operation every time it needs to restore the pressure.ón necessary of the system that requires it.
Since the PTU pump is located in the central part of the aircraftón, passengers directly above it, especially seats that are in the positions on the wings are those that usually hear the sound with más intensity while the passengers who are más ahead they don't usually notice it too much.
Now we know that this famous sound of “barking dog” It's part of the operationón normal aircraft systemsón and we should not worry that someone locked upó still poor little animal in the cargo hold or that there is somethingún problem with the avión.
T I congratulate very good post.
I would like you to make a post explaining how I know the A/C works on airplanes.
a very interesting topic, let's investigate it.
so that was it!
Thank you very much for the clarification, I recently flew in an A 320 in a central seat but the strange thing was that throughout the flight he did, hour and 20 minutes, The flight attendant told me that it was a failure of the hydraulic system without any problem., when mentioning hydraulic I thought landing gear, when arriving at the airport, I expected to see the firemen and ambulances, What a scare!
Sometimes happens, very little, but it happens, in the end there is no problem.
excellent report, I thought they were the landing gear doors..
nice louis! Thank you for reading.
The sound is more like the co-pilot sawing the pilot's floor haha
He looks like a DJ scratching a record lol
The truth is I always wanted to know what that sound was but I could never find a good answer thank you very much for explaining that sound, now when I go by plane I'll be calmer. Otra duda que tengo es que en el aeropuerto de quito en una de las cabeceras de la pista en la última salida hay como una «oreja» justo entre la calle de rodaje y la curva para entrar a la pista y siempre me pregunte que era y me preguntaba si podrias investigar sobre eso porque me tiene algo confundido. A very good job in this post and in all, I've been following you for more than a year and I admire you a lot, keep it up.
Hi Joaquin, It's good that your question was resolved.. About your question, that ear is just that, an ear where planes can park for testing.
Thank you very much I always wondered what it was and now I finally know. I love your blog and I see it every day I hope you continue posting like this for a long time, I wish you the best. Successes!
Thanks!