Specific Comments about RNAV Implementation and the Socal Metroplex Draft Environmental Assessment.
The central community issue with the FAA’s implementation of RNAV flight paths is they take wide dispersed flow of aircraft paths and focus them into a concentration of flights around a centerline.
The modeling needs to accurately reflect the anticipated noise impacts from the proposed changes and communicate them to the public.
Instead there is confusion about the results, a lack of clarity of the changes, and aside from some specific points on specific flight paths being lowered or moved, a general forfeiture of understanding and belief. This is counter to the type of clarity a project needs to move forward.
The general questions I have are:
1.) What is the FAA doing differently to prevent the increased and concentrated ground noise, annoyance and complaints that occurred with RNAV deployment at other airports and communities such as Pheonix, Palo Alto, Queens, Charlotte, Chicago, Minneapolis and Boston, and will the implementation here have the same problems?
- For all operations, below 10,000 ft, will the the design team keep established elevations and/or raise them higher?
- Are areas of existing noise going to get any relief?
- Will any movements of flight paths be sensitive to residents and not just be a shifting from one community to another?
- How does the FAA plan to mitigate the noise from a steady and repetitive stream of flights that will be created by narrowed RNAV corridors? And why is this missing from the EA?
- What are the NextGen’s priorities between air traffic flexibility, efficiency and a populations annoyance level?
Despite the efforts of the EA it seems difficult to accurately gauge the noise impacts without additional metrics, study and data. An attitude of “we won’t know until it’s implemented” demonstrates the limitations of the draft Environmental Assessment. The concerns of communication and clarity will be better addressed by a more robust EIS.
In the event an EIS is not performed:
2.) Can additional feedback periods be planned for the next iteration of an EA ( if not proceeding to an EIS), and immediately after implementation?
How were RNAV/RNP’s modeled?
For people to understand the changes an accurate and complete noise modeling is to be expected. At the FAA public hearings I had numerous conversations with Noise Analysts about RNAVs. The first technical question I wanted answered was:
3.)”How was the flight track data modeled to conform to RNAV/RNP expectations?”
Surely the FAA has learned from its mistakes. They must have stacks of statistical equations and studies of existing RNAV usage to help predict distribution and and modify future planning.
The answer I received: “The noise analysts took existing flight tracks and centered them over the new waypoints.”
Limitations of how the EA “modeled” the RNAVs.
Another question I asked was “Did you reshape, or redistribute the flight tracks in any way to make them conform to RNAV or RNP distribution rules and lateral boundaries?”
The Answer I received was “We shaped the outside contours to fit within the expected outer boundary.” The authors of a paper documenting the procedure claimed that no reshaping was done  so this is an interesting point of disagreement.
4.) Can the FAA supply the correct answer to this?
Using the nominal (as-is) flight tracks may give an adequate result when one RNAV is replacing another but it will completely fall apart when the new RNAV is significantly different. In addition a more laterally restrictive RNP final approach procedure will be completely inaccurate. Dispersion modeling of new RNAV and RNP procedures through a statistical analysis of past RNAV/RNP or using a formulaic distribution model will yield a more accurate result of expectations and future traffic.
The expectation of RNAV and RNP is a concentration of flights along the flight path centerline. This increase in operations along a fixed path would result in an increase in noise effects, Specifically recognized by metrics such as N60 or N70 (number of airplane related noise events above 60 or 70dB) and represented by DNL, along the centerline, and a decrease at the outer boundary.
Number of Aircraft flying the RNAV
It is assumed that not all aircraft will fly the RNAV. Statement of the exact number of RNAV users is required for noise modeling and needs to be explicit in the EA. An FAA ATC rep shared at the LAX public meeting that only 30% of the aircraft are expected to fly the RNAV. This number is based off the number of current flights that currently use IFR.
The Study team estimated that 90% of LAX aircraft are RNAV capable. To fly RNP the planes FMC needs to be RNP-0.3 capable and the fleets must train the operators, and be approved. Industry source suggest the RNAV capable aircraft is 95%.
Culver City is in the North downwind leg of LAX. The IFR plates for the SADDE SIX STAR that routes arrivals into the downwind leg has this to say about how to fly over Culver City:
“..From over SADDE INT via SMO R-261 to SMO VOR/DME, then via SMO R-068 to SMO 9 DME for Runways 24 and 25. From SMO 9 DME expect vector to final approach course for Los Angeles Intl Airport.” The ATC issue these instructions: “..cross Santa Monica VOR at 7000, descend and maintain at 2500.”
The low number of aircraft following IFR is probably due to it not offering much benefit while under clear skies. GPS RNAV is very different than current IFR and linking them will not yield an accurate estimate. Even without the NextGen Program the flying public has been wanting better integration of satellite navigation.
5.) The percentage of planes expected to utilize RNAV and RNP is not explicitly stated in the EA and requires arguments to support why this number is chosen. .
6.) What values for frequency of RNAV vs conventional flight tracks were used in the noise modeling? The noise analysis assumptions needs to be verified and explicitly stated so as not to be arbitrary.
What are possible RNAV mitigations
7.) Is it possible to deploy Satellite navigation efficiencies without the concentration of disadvantages of the current NextGen deployment. With procedures that use appropriate distances and altitudes to minimize noise impact?
8.) How far away is the technology, or is it possible now, to deploy multiple dispersed flight paths within an RNAV corridor that will more equitably distribute noise over a larger area?
9.) What new mitigation strategies will you be deploying to communities burdened with RNAV overflights? Will you fold them into noise mitigation programs reserved for 65DB DNL, will you supplement funding by RNAV users, the NextGen Program or other source?
10.) DNL doesn’t seem adequate to describe the situation of a concentrated flight paths effects. Can a supplemental metric such as N60 or N70 be used to describe this to the public?
“Super Density Operations Airspace Modeling for the Southern California Metroplex, AIAA Modeling and Simulation Technologies Conference,, Sebastian D. Timar, 2011”
*A nautical mile represents a minute of arc or 160th of a degree along a meridian or great circle. Its continued use makes chart reading easier as grid spacing is one minute of latitude.