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[viking133]

I am just wondering why there is an "alarming" kinda "whoop-whoop" sound in the cabin during start-up. I always hear it when flying SAS MD-80s, but not on other operators MDs.

[bafanguy]

If the sound appears to be coming through the cabin speaker system, and stops after engine start, you're probably hearing the engine ignitor plugs firing during start.

[Lame]

We operated MD80s from SAS, and the only thing I can think of that made a noise like that is the hydraulic pumps.

I believe some operators turn them off during start, but if you leave them on as we did, it could be that.

[bafanguy]

Lame,

I thought about that, but on the -80, the trans pump doesn't make the loud cycling noise like the aux gear pump does on the -9.  And the aux pump just makes its loud, incredibly obnoxious, steady whine on both airplanes.

I'm guessing ignitor plugs on this one.   

Need to get more details from viking133... 

[Lame]

The hydraulics were very noisy on the SAS MD80s we operated.

Mind you SAS leased us all their worst ones.

[viking133]

Hmm, I know that the hyd pumps where off (or set to low...probably off though), not sure about the aux/transfer pumps. And yeah, it's a cycling sound...like a sinus curve or a world-war two alarm in fast forward. And I think it doesn't last exactly as long as the start-up sequenze...you hear it during push-back.

[bafanguy]

viking133,

My vote still goes with ignitor plugs based on what you've said.   

[Lame]

I am just wondering why there is an "alarming" kinda "whoop-whoop" sound in the cabin during start-up. I always hear it when flying SAS MD-80s, but not on other operators MDs.

IF the original question is correct, how do all the other operators manage to start their JT8Ds without igniter plugs? 

Everyone has to use igniter plugs to start the engines, that is why I was trying to think of something that may vary from operator to operator, like some have hydraulic pumps on and some don't.
 

[viking133]

I also think it is the igniter plugs now as I've been asking around a bit. Maybe SAS uses another PA-system than the other operators or maybe it's just that the flight attendents on other operators MDs actually have noticed that the sound is pretty annoying and manage to shut-up during start-up 

[Tjosan]

It is the ignition that sounds in the cabin during engine start and push back.

[dolmo333]

Was going to ask the same question but then i saw this thread. I think this video say it all: http://www.flightlevel350.com/Aircraft_McDonnell_Douglas_MD-87-Airline_Scandinavian_Airlines_-_SAS_Aviation_Video-7299.html
As you can hear it is in the same time when the engine ignites so the ignition may well be the answer.

As the same time i can ask about the classic beeping sound in the MD in the PA. It?s one of the coolest things about the MD80 series. It's heard on the 737 series as well as the 747 classic series in some aircraft. Also in the Fokker 50.........well it?s in a lot of aircraft. You can also hear it on the above video. I have a feeling that it?s the generators sounding or the inverters? Something electrical it is for shure. And why is this sound only heard in most MD?s but not all?

/Daniel

[landy]

I know this "whoo-whoo" sound at engine start quite well from flying with the Fordair MD-87's which now both are flying with Allegiant. In my opinion this sound comes up when both engines are not running on exactly the same revs.
German bombers were famous in WWII for generating such strange sound due to their unsynchronized engines.
I think it's the same effect in the MD-87 until both engines run on the same revs.
Regards: Guido

[Tempsto]

I just saw this old thread.

I fly MD80 in SAS and agree with bafanguy that it's the ignitor plugs that makes the sound viking133 describes. I guess the reason that it's heard more often on SAS' MD80s is because there's an almost constant use of the PA from either cabin crew or from the flightdeck (due various company procedures). These procedures causes the cabin crew to start the "safety announcement and demonstration" at push back and the engines will also be started at the same time - causing the alarming sound to be heard through the loudspeakers. A friend of mine who often rides MD's enquired me about the sound a few months ago. He thought it was in order to get the attention of the pax during the safety demonstration.

The sound landy describes is due to the engines not running at the same revs as he wrote, and this won't go away until the engine synchronizer is switched on during climb (it's just not audible at T/O thrust).

Best regards.
TS