Is a 4 degree glide slope practical ?

[Admiral346]

so what really happens on a 4° slope?

You have to start configuring much earlier, like it has been said, in Marseille you should start the ILS with flaps 20°, or you won't stand a chance (that is in the CRJ -700-900). On a 3° glide I can delay flaps 20 to around 2000' AGL if not speedrestricted by ATC. I also can delay the gear.

On modern aircraft the majotity of the noise is created by interference of slipstream around gear/flaps. The engines are at idle anyways and only give off a slight hiss, until - yes, just until - I have to start stabilising my approach by getting flaps and gear down and increasing engine power. Then the noise really starts...

So what do you gain by shifting to a 4° glide? - In theory, aircraft would fly about 30% higher off the ground, so at 10 miles 4000 iso 3000 feet - that is a gain, no doubt, and a big noise reduction.
Now at 6 miles out 2600 iso 2000 feet, still some advantage...
At 3 nm 1300 iso 1000 feet - not much difference.

Unfortunatly it won't really work that way - You have to get the flaps out at 10 nm, increasing the noise (remember, you don't fly slower, you just need more drag to maintain speed), somewhere between 10 and 7 nm you would need the gear to go down (on a CRJ - on an A330 starting down with anything less then gear down and flaps 2 would lead to a goaround). Final configuration must be achieved earlier to get down to Vapp, thereby increasing noise levels...

I think if a 4° slope wouldn't increase noise levels, they ought to be about the same, with a huge downside on safety - less stable approaches, higher rates of descent,...

In my opinion. not an option at all...

Nic

edit:
PS: The most silent approaches can be achieved at airports with little or no traffic, where ATC doesn't get in your way.
You just glide it down, and set it up to have the right speed and little flap hitting the glide at the descent point, take it down the ILS and drop everything at 1800 to 1500 feet AGL, to be established at 1000' exactly, not moving the throttles out of idle all the way...

Most satisfying, when done right...

Nic