View Full Version : Strange squeeks on easyJet?
Chris777
24th Jul 2007, 20:31
I flew with easyJet from Palermo to Gatwick on Saturday and was completely baffled by a squeeking sound (like someone polishing a window, but a lot louder) which came from the aircraft as we taxied to the runway. The same sound, but much louder (starting quickly and slowing down) happened as we parked up at Gatwick. It was an Airbus. What on earth was this?
UniFoxOs
25th Jul 2007, 08:57
Disc brake?? Was it related to the speed of the a/c?
UFO
There have been discussions of this noise here on PPRuNe before.
You were on an A319.
It is the hydraulic system equalizer. There are duplicated hydraulic systems powered one from each engine. If one system's power source fails a pressure equalizing valve automatically operates to pump pressure from one system to the other, this is what makes the noise. It is noticeable only in the part of the cabin over the valve.
The pump will operate when one engine is started, or shut down, before the other, and the pressure in the associated hydraulic systems differs. This is why you got the noise when on the ground. It is a feature of most A320-series flights.
Like a number of other noticeable aircraft noises (the BAe 146 flap extension noise etc) the manufacturer has developed a modification for it, but it is cost and weight and therefore doesn't tend to get adopted.
You'll get the best answers posting this on the Engineers and Technicians forum Chris.
Final 3 Greens
26th Jul 2007, 12:14
FHA
Untrue.
WHBM describes the cause of the noise.
The noise making unit is called a PTU.
Untrue?
Why would asking the people who maintain the aircraft for a living not be the best option?:confused:
I've got the A320 series on my engineer's licence, so I know what the PTU does.
Chris, the Power Transfer Unit is a device which enables transfer of hydraulic power from one system to another. It activates automatically (provided, if I remember rightly, the mode switch is in 'auto' as per normal procedures) under certain conditions and is also automatically tested on pushback after the second engine start. The design is such that the Yellow and Green (as they are coded) systems remain hydraulically de-coupled despite being able to drive the other. This ensures that a leak in one system doesn't drain the contents of the other.
It is chuffing noisy and sounds like someone is sawing the fuselage in half! Is this the noise you're referring to?
I know what the PTU does. The description given was slightly innacurate.
Oh dear. I was reducing it to plain words interested pax (as this is their forum) would be OK with. "PTU" isn't even in Wikipedia.
Chris, there's a more technical description starting at Page 9 here :
www.ricardis.tudelft.nl/~kris/LightsAndSwitches.pdf
WHBM.
Sorry about that mate, you articulated well.:ok:
I was just in the process of editing my post! Admittedly, on the engineers' forum you can get blinded by science but most of the pax who post on here seem pretty switched on.
Keep flying!
Techman
26th Jul 2007, 16:35
I have to agree with FHA, even though he is a Fairy.
If you are going to make inaccurate descriptions of systems, at least qualify your post as such.
I have to agree with FHA, even though he is a Fairy.
Please note the capital 'F' dear Ppruners!:):)
Are you still flying Techman or is it all ground engineering these days?
TightSlot
26th Jul 2007, 19:46
Gingers - many thanks for the definitive answers.