The FAA has begun implementing new arrival procedures across the nation. These new procedures, called Continuous Descent Approaches (CDAs), decrease noise and emissions when used at night or in low-traffic environments. However, when CDAs are implemented in high-traffic environments, as they were done at LAX, they result in increased noise and emissions.
On October 24, 2007, Carl Burleson of the FAA, testified to the House aviation subcommittee concerning the benefits of Continuous Descent Approaches (CDAs), which is part of the Next Generation airspace modernization.
He testified that, “You can see in Chart 6 the results of a demonstration of CDA at Louisville Airport – and significant reduction in areas of exposure to aircraft noise. CDA is one of those win-win strategies, having environmental and economic benefits, that can reduce noise, emissions and fuel burn, as well as flight time.”
What the testimony did not reveal was that the analysis was for nighttime Continuous Descent approach procedures for Louisville Airport.
While the benefits derived for the nighttime arrivals at the Louisville airport are well documented scientifically, the implementation of full-time CDAs at LAX were done with altitudes that were exactly opposite as to what was done at Louisville.
What this means is that noise (especially for those from 15-30 miles away from the airport) and emissions/pollution have actually increased in communities surrounding LAX.
The benefits of CDAs, as outlined in the nighttime Louisville study, concerning altitude profiles, are outlined on page 56 and state the following:
As shown, the two aircraft that performed the conventional approach descended sooner and thus flew lower over the community. The figure clearly shows the conventional flights performed step down descents.
Between 15 and 20 nm away from the runway, CDA flights were up to 1,500 ft higher. This is one of the reasons why CDA has a lower noise impact than conventional approaches.
However, when you look at the vertical profiles of current CDAs being flown into LAX, which were compiled by the Los Angeles World Airport staff, you can see on page 6 and 7 that the CDA altitudes at 20nm away are anywhere from 617 feet to 1101 feet lower than the conventional, pre-CDA altitudes. Because of this, LAX has more noise and emissions after the implementation of CDAs into LAX than before CDAs.
The reason that the vertical altitudes are so significantly lower at LAX using CDAs is due to the fact that CDAs, when utilized in high traffic environments, must be kept flying at low altitudes so that the planes do not catch up with each other.
In fact, Eurocontrol, which built upon the work started at the Louisville airport, said in a report presented at the 29th IEEE/AIAA Digital Avionics Systems Conference on October 3-7, 2010 that:
Abstract – Continuous Descent Approaches (CDAs) can significantly
reduce fuel burn and noise impact by keeping arriving
aircraft at their cruise altitude for longer than during conventional
approaches(to descend as late as possible)and then having
them make a continuous descent to the runway at near idle
thrust with no level flight segments. The CDA procedures are
fixed routes that are vertically optimized.
Noise-efficient operations, such as Continuous Descent Approaches
(CDAs), can significantly reduce the noise impact
of landing aircraft by keeping aircraft at higher altitudes
on approach to the airport and by reducing power during
descent [5], [6].
Eurocontrol also said in the same report on page 9 under “Multiple Aircraft Scenario” that:
CDA operations are usually conducted at night and/or in
low traffic conditions. One reason is that for CDA, the landing
interval has to increase to guarantee sufficient spacing between
aircraft on the final landing segment [28]. The increased
landing interval is necessary because of the large dispersion in
aircraft approach speeds.
In addition to the supposed noise benefits of CDAs, based upon the nighttime Louisville study, the FAA asserted that emissions would be less utilizing CDAs, as the jets spent less time under 3000 feet in the Louisville study. Page 73 of the report states:
As was seen in Figure 6-2 and figure 10-1, conventional aircraft are typical vectored at significant distances at low altitude thus spending greater time below the mixing height of 3000 feet AGL. Further analysis confirmed that the greater time that the aircraft is spending below the mixing height is overwhelming the slight decrease in the CO emission rate that occurs at the higher throttle settings that are typical of the conventional approach.
However, because CDAs spend more time under 3000 feet at LAX, as noted on the 24R – Arrival Flight comparison done by the Los Angeles World Airport (page 7), and the CDA lower throttle gives off more CO emissions, than the CDA at LAX is clearly creating more emissions/pollution when compared to the conventional approach.
All of the benefits of CDAs are extrapolated based upon the results of the nighttime Louisville airport study. Unfortunately, because the data (altitude descents) utilized to formulate the conclusions are inversed when evaluating LAX, the reports cannot continue to support that the same noise and emission/pollution benefits apply. And, in fact, there is increased noise and emissions when the FAA’s own theories, explained in the Louisville study, are used with LAX altitude data.
Residents located within 40 miles of major airports should be very concerned about plans to institute CDA procedures into their airport.