Re: 757 Engine noise over LA

Date:         04 Jun 97 13:03:57 
From:         smarko@aol.com (SMARKO)
Organization: AOL http://www.aol.com
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>I was on a Delta Airlines flight (550) from LAX to Atlanta on the 22nd
>of December 1996 (on a 757).  As we took off from LAX with a full load,
>I could (obviously) hear the engines at near full (if not full) power.
>About 30 seconds after take off, as we crossed the coast line (taking off
>towards the west) both engines went suddenly very quiet.
...
>I though this cut off might be something to do with any noise abatement
>rules over the LA area, however, when I took this same flight on March 28
>this year, under the same conditions of a loaded 757, there was NO change
>in engine noise after take off.

At LAX, airplanes normally depart to the west, over the ocean, largely for
noise abatement purposes. Perpendicular to and above the departing
traffic, parallel the coastline, is a VFR corridor at about 5000 feet. I
would imagine that the first 757 cut back over the ocean in part to avoid
climbing into the cross-traffic above it. Once the plane was beyond the
VFR corridor, it resumed its climb. The second flight was probably not
climbing as fast and could maintain separation while continuing its climb.

The two flights took different SIDs (standard instrument departures),
accounting for the different flight paths. The use of certain SIDs is
restricted during certain hours of the day, also for noise abatement
purposes.

Mark Adams
Noise Management Bureau
Los Angeles International Airport