Oscillating whirring sound at aft of A380 main deck

[SQ747]

Some of you (who fly YCL) may have noticed the strange whirring sound at the very back of the A380. It's loudest in the main deck lavatories or around the staircase, and seems to always be oscillating up and down whilst the A/C is on the ground. It does also start up in the air sometimes, however I've found it may only do so during descent.

Any idea what this is? Is it some sort of pump? Or the actuators that move the rudder/ flaps? It is very regular and continuous on the ground, though. Just curious!

[ninervictor]

APU maybe?

I hear the same on my flight to JFK on SQ26
Was seated on Row 55 at the rear

[boing]

I think you are referring to the toilet vacuum blower. Operates every time someone presses the toilet flush to provide the suction force. It is deactivated automatically at 16000 ft as the differential pressure takes over to provide the suction force.

[yflyer]

I think you are referring to the toilet vacuum blower. Operates every time someone presses the toilet flush to provide the suction force. It is deactivated automatically at 16000 ft as the differential pressure takes over to provide the suction force.

I don't think it is the sound of the toilet flushing. That is quite loud too, but happens only when someone flushes.

The sound SQ747 is referring to is a low whirring sound, alternately rising and falling in pitch, that I have also noticed, which seems independent of toilet usage. My guess would also be the APU or some sort of ventilation / hydraulic function.

Another characteristic of the A380 is a very silent final approach and landing: it almost glides onto the runway. Unfortunately, it seems that the A380 can also land quite hard on some occasions. Put them together, and you get what happened on a recent SQ CDG-SIN flight I took. The plane was near silent as we landed at Changi, but it landed hard, with a very loud crunch, which startled the pax around me and set off a lot of nervous laughter and chatter as we taxied to the gate.

While on the topic of distinctive sounds, others which come to mind are the "barking dog" hydraulics of an A320 (Google "A320 barking dog" for more!), and the loud, growling low notes that a GE90 engine on a 777-300ER makes when starting up, one side at a time.

[loldude333]

I don't think it is the sound of the toilet flushing. That is quite loud too, but happens only when someone flushes.

The sound SQ747 is referring to is a low whirring sound, alternately rising and falling in pitch, that I have also noticed, which seems independent of toilet usage. My guess would also be the APU or some sort of ventilation / hydraulic function.

Another characteristic of the A380 is a very silent final approach and landing: it almost glides onto the runway. Unfortunately, it seems that the A380 can also land quite hard on some occasions. Put them together, and you get what happened on a recent SQ CDG-SIN flight I took. The plane was near silent as we landed at Changi, but it landed hard, with a very loud crunch, which startled the pax around me and set off a lot of nervous laughter and chatter as we taxied to the gate.

While on the topic of distinctive sounds, others which come to mind are the "barking dog" hydraulics of an A320 (Google "A320 barking dog" for more!), and the loud, growling low notes that a GE90 engine on a 777-300ER makes when starting up, one side at a time.

On a completely unrelated but related note, i LOVE the sound of those GE90-115Bs starting up and spooling up for takeoff. Probably my favourite noises when flying!

[ninervictor]

On a completely unrelated but related note, i LOVE the sound of those GE90-115Bs starting up and spooling up for takeoff. Probably my favourite noises when flying!

I love the spooling up during take off

[boing]

I don't think it is the sound of the toilet flushing. That is quite loud too, but happens only when someone flushes.

The sound SQ747 is referring to is a low whirring sound, alternately rising and falling in pitch, that I have also noticed, which seems independent of toilet usage. My guess would also be the APU or some sort of ventilation / hydraulic function.

Another characteristic of the A380 is a very silent final approach and landing: it almost glides onto the runway. Unfortunately, it seems that the A380 can also land quite hard on some occasions. Put them together, and you get what happened on a recent SQ CDG-SIN flight I took. The plane was near silent as we landed at Changi, but it landed hard, with a very loud crunch, which startled the pax around me and set off a lot of nervous laughter and chatter as we taxied to the gate.

While on the topic of distinctive sounds, others which come to mind are the "barking dog" hydraulics of an A320 (Google "A320 barking dog" for more!), and the loud, growling low notes that a GE90 engine on a 777-300ER makes when starting up, one side at a time.

I wasn't referring to the sound of toilet flushing. Rather, it's the sound of the motor that provides the suction. It's located at the back of the cargo compartment. It's activated whenever any of the lavatories on the aircraft is flushed. To recreate it, you can to any of the aft most lavatory. When you press the flush button, you should hear this sound about w to 3 seconds before the "flush" and it will switch off about 2 seconds after the "flush" has stopped.

[sabian]

Does it sound like this?

http://www.youtube.com/watch?v=zZ7CoGl9hTM

[SQ747]

Interesting. It could be the toilet vacuum, but it's regular and continuous. Doesn't just happen when you press the flush button. Can also he heard in the staircase and the very aft of the upper deck. APU perhaps, although I swear I've heard it while on descent.