N126DL
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DC-9-50 Engine Start Noises

Fri Aug 24, 2012 9:10 pm

Anyone know why the DC-9-50 engines have a strange noise upon startup? Is it a difference between the JT8D-17 and the JT8D-219's on the MD-88 which don't make that noise?

http://www.youtube.com/watch?v=swWfoPF1F3A
at around 00:30 mark - the whoop whoop whoop
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zanl188
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RE: DC-9-50 Engine Start Noises

Fri Aug 24, 2012 9:42 pm

Sounds like a flight deck alarm to me.... Configuration or Master Caution maybe?
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tb727
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RE: DC-9-50 Engine Start Noises

Fri Aug 24, 2012 10:19 pm

I have no idea, we have a 727 or 2 that does it too, I've heard it in Learjets and Falcons I have flown too. I think it has something to do with the igniters.
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XFSUgimpLB41X
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RE: DC-9-50 Engine Start Noises

Fri Aug 24, 2012 11:03 pm

It's when the fuel lever is brought from cutoff to run and the starter is engaged.
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flashmeister
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RE: DC-9-50 Engine Start Noises

Fri Aug 24, 2012 11:11 pm

Check out this thread: Two DC9 Questions (by DrDeke Nov 15 2006 in Tech Ops)

What you're hearing is interference in the PA system caused by the ignitors firing.
 
FlyASAGuy2005
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RE: DC-9-50 Engine Start Noises

Sat Aug 25, 2012 3:28 am

Something that's always been on my mind...what is that almost "bang" sound you ear right at the end of the 88's engine start right before final spool? It's very hard to explain but as the engines turn and gain EPR you hear a sort of bang, the engine sounds goes up (as if you're spooling up) then it settles. It's right at the end of the engine start.
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N243NW
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RE: DC-9-50 Engine Start Noises

Sat Aug 25, 2012 5:47 pm

Quoting FlyASAGuy2005 (Reply 5):
Something that's always been on my mind...what is that almost "bang" sound you ear right at the end of the 88's engine start right before final spool? It's very hard to explain but as the engines turn and gain EPR you hear a sort of bang, the engine sounds goes up (as if you're spooling up) then it settles. It's right at the end of the engine start.

You're probably hearing the fuel being introduced, which on the JT8D produces a terrific and very pronounced light-off sound. It's right at 1:05 in this video, but (of course) some baby has to be making noise at the same time so it's hard to hear. http://www.youtube.com/watch?v=jwwhKYaLBTc
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PGNCS
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RE: DC-9-50 Engine Start Noises

Sat Aug 25, 2012 8:45 pm

It's the ignition system used for engine starts.
 
FlyASAGuy2005
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RE: DC-9-50 Engine Start Noises

Sun Aug 26, 2012 3:17 am

Quoting N243NW (Reply 6):

That's the exact sound I was talking about (timing). It wasn't as pronounced in this video bu that was it.
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N243NW
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RE: DC-9-50 Engine Start Noises

Sun Aug 26, 2012 5:42 am

Quoting FlyASAGuy2005 (Reply 8):

That's the exact sound I was talking about (timing). It wasn't as pronounced in this video bu that was it.

That's what I figured. Funny thing is - it seems to be the loudest just behind the wing. If you're sitting right next to the engine, from my experience at least, it is definitely audible but not quite as loud.
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AmericanAirFan
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RE: DC-9-50 Engine Start Noises

Sun Aug 26, 2012 4:38 pm

Quoting N243NW (Reply 6):
You're probably hearing the fuel being introduced, which on the JT8D produces a terrific and very pronounced light-off sound.

I got really lucky while taking shots of an Allegiant MD-87 from its backside. I was taking 1" exposures because the light was low. It was hand held. I had no idea that I caught the fuel introduction until I got home and looked through my photos.

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NWADC9
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RE: DC-9-50 Engine Start Noises

Sun Aug 26, 2012 10:45 pm

Why is this "whoop whoop" found on DC-9s and not MD-80s? Was there an improvement with the JT8D-200 series that did away with this sweet song?
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N243NW
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RE: DC-9-50 Engine Start Noises

Mon Aug 27, 2012 12:21 am

Quoting AmericanAirFan (Reply 10):
I got really lucky while taking shots of an Allegiant MD-87 from its backside.

Nice catch!  

Quoting NWADC9 (Reply 11):
Why is this "whoop whoop" found on DC-9s and not MD-80s? Was there an improvement with the JT8D-200 series that did away with this sweet song?

I have heard it on several AA planes, although it seems to vary from one aircraft to another. Some are silent, while others are very pronounced.
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boeingfixer
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RE: DC-9-50 Engine Start Noises

Tue Aug 28, 2012 2:07 pm

Quoting flashmeister (Reply 4):
What you're hearing is interference in the PA system caused by the ignitors firing.

To be technically correct what you are hearing is the ignition box recharging between firing the ignition plugs. The pause in the sound is the actual moment of ignition plug firing.

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Accidentally
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RE: DC-9-50 Engine Start Noises

Fri Aug 31, 2012 4:50 am

It's to do with the ignition system. Kinda like the quick ticking from a King Air's PT6. In that video you posted there's a video down below titled "Delta Airlines DC-9-51 Start-up, Takeoff, Cruise MKE-DTW Pt. 1/2" in which it is also evident.
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SPREE34
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RE: DC-9-50 Engine Start Noises

Sun Sep 02, 2012 3:08 am

Quoting boeingfixer (Reply 13):
To be technically correct what you are hearing is the ignition box recharging between firing the ignition plugs. The pause in the sound is the actual moment of ignition plug firing.

This. ^^^^^^^

You hear it in headsets in the cocpit too. 80s and later aircraft had better isolation of electricl noises from the audio equip. 400hz hum used to be common in AG comms and PA announcements. Hardly heard anymore.
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IAHFLYR
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RE: DC-9-50 Engine Start Noises

Wed Sep 05, 2012 9:37 pm

Quoting SPREE34 (Reply 15):
You hear it in headsets in the cocpit too. 80s and later aircraft had better isolation of electricl noises from the audio equip. 400hz hum used to be common in AG comms and PA announcements. Hardly heard anymore.



I still find it often on the AA Super 80 fleet more so than the DL MD88's.
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KingAir200
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RE: DC-9-50 Engine Start Noises

Thu Sep 06, 2012 4:33 pm

Quoting SPREE34 (Reply 15):
You hear it in headsets in the cocpit too.

It seems to vary from ship to ship, but it can be quite loud over the ramp interphone as well.

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