Below are some comments and specific feedback on the assumptions about the mix of airplanes used in modeling the noise data. Comments are specific to LAX aircraft aggregation and is also intended to be applicable as a general comment to other airports.
Segmentation of Night time operations are not represented
1.) During daytime the LAX airport operates in a predominately West-flow orientation where aircraft land on the East side and depart on the West. The EA assumes nightime as 10pm -6:30am. At LAX, nighttime operations consists of 2 operating modes:
- From 10pm to midnight the airport continues its West-flow operations.
- From midnight to 6:30am, the airport operates in an Over-Ocean mode where aircraft take off and land from the West side.
This results in a segmentation of the nighttime operations, as well as a switch in origin, carriers, fleet mix and possibly category that fly over the areas parallel to the airport during this late-night. This segmentation should be reflected in the modeling.
Each STAR/SID has a unique mix of aircraft
2.) Each STAR and SID route has a different mix of aircraft which use it. The noise analysis only identifies aircraft on a per airport basis, not per route. This will result in inaccurate results. LAX airport has 3 significant STARs, which are used disproportionately by different carriers- each carrier uses a specific fleet mix of aircraft.
For instance the SADDE STAR, which collects aircraft from the Pacific Ocean and north, has Quantas, Korean, All Nippon Airways, Air China, CargoLux, China Southern, Nippon Cargo, Polar Air Cargo. These don’t use any other STAR and tend to be heavier planes. The HUULL STAR was created specifically to carry heavy planes from the Pacific.
To be accurate, the Noise model need to represent the appropriate aircraft that fly each of the airport’s major STARs and SIDs.
Normalization needs support
3.) The researchers used dataset normalization of aircraft. This is done when complete information is missing in this case data on arrivals did not equal departures for some reason. The airport is a closed system so Arrivals and departures should naturally balanced at 50% each. Aircraft should be tracked in/out to make normalization unnecessary. In order to ensure that the amount of missing data isn’t statistically significant the amount of normalization needs to be stated. In addition normalization doesn’t take into account the following conditions:
- Due to the LAX airport daily change in operations direction it doesn’t mean that in/out are balanced between the daytime and nightime operation modes. ( see previous comment)
- Some aircraft operate on legs where their destination is different than their origin. This results in a difference in direction that may weight one side of the airport to have a different fleet characteristics.
Normalization can’t be arbitrary and aircraft must be tracked to represent actual airport conditions.
Fleet mix assumptions do not accommodate evolution/change over time
4.) From the EA’s NTR: “It was assumed that the percentages of 2015 and 2020 itinerant IFR AAD operations occurring during daytime and nighttime hours by aircraft category and type of operation would remain constant for each Study Airport from 2013 to 2015 and 2020.” This doesn’t allow for obsolescence and introduction of new aircraft, or growth of fleet to larger aircraft. The modeling of the 2015 flight tracks will already be inaccurate due to using the 2012-2014 fleet mix, the modeling of 2020 noise will exaggerate this inaccuracy. 2020 should use a modified fleet mix that incorporates air fleets planned aircraft changes.