Not completely sure but i think you are mixing up 2 things at once. On the
engine deal, there is a thing called FADEC which limits the engines. That is
Full Authority Digital Engine Control which is on many of the newer airliners.
The easiest way to describe this is you overbuild the engine power wise and
then derate it down to a more reasonable thruat and that in the long run will
give you the same power but a lower fuel consumption. Best aircraft is the
Boeing 777. Some of the engines on it are capable of up to 115,000 lbs/thrust
each. The pilot may only have access to lets say 90,000 lbs/thrust per engine.
By overbuilding the engine and limiting it, it saves fuel and wear on the engine
since the engine doesn't have to be at full power. Lets say you now have an
engine max rated at 90,000 lbs/thrust each. On takeoff the pilot would have
to have the engines at full power, and since this is the absolute max that the
engine can do, it is causing a little extra wear and drinking a whole lot of more
Now for the deflectors at the end of the runway it depends on the airport.
There are probably many reasons why they are there but mostly since there
might be a building or a highway on the other side of the blast fence.
On the noise level, I am not completely sure but I do know that certain aircraft
cannot operate at some airports due to the noise abatement procedures. That
mostly applies to the older aircraft for instance the 727,737-200,707. Since
the older engines are a lot louder at takeoff power that the newer engines.
That is where the FAA mandated the hush kit mods to all aircraft and they
have to be at a certain decibel level or below. My home in Tennessee, the
local airport banned some of older aircraft due to excessive noise. The mainly
banned the older Lears and Gulfstream's. To prove the noise difference, we
have several old Lear 24's that fly alot. At full power it sounds almost identical
to an F-16 at full power plus 1/4th afterburner. Thats loud. It all depends on the airport.