|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.
|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.
|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.
|Quoting AmericanAirFan (Reply 10):|
I got really lucky while taking shots of an Allegiant MD-87 from its backside.
|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?
|Quoting flashmeister (Reply 4):|
What you're hearing is interference in the PA system caused by the ignitors firing.
|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.
|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.