Your Questions Answered

During the 2020 program, we had such a great success with the use of for our Q&A discussions that we didn't have enough time to answer all the questions that were posed. Below our committee has collected a few responses for the unanswered questions of slido. While we have not been able to obtain full responses to all questions, we are grateful that some speakers took extra time to address theirs. 

Please note that these question answers are for event attendees only. Many of the questions must accompany the context and specific situation that was explained in each presentation and therefore should not be held as stand-alone answers to every situation. These answers are only meant to compliment the presentation discussion that was held at the symposium. 

Legislation and Implementation: The 2018 FAA Reauthorization Act and What Congress and FAA Have Been up to since

Veronica Bradley: 

  • Where does A4A stand on the potential for future noise restrictions and curfews due to proposed legislation eliminating ANCA?
    • A4A and our members have been keenly focused on aircraft noise reduction efforts for many years and have in fact reduced the number of people in the U.S. exposed to significant aircraft noise by 94% between 1975 and year-end 2018, while enplanements rose 359%. These reductions have been achieved primarily through a reduction of noise at the aircraft source, through the adoption of technological improvements reducing aircraft engine and airframe noise, airline purchase of newer, quieter aircraft and the use of operational procedures that further abate noise. A4A supports current FAA noise standards and noise policy requirements to reduce the industry’s noise impact because technology and operations continue to drive noise reductions. Any additional restrictions to limit noise exposure in other ways, e.g., curfews, must take into consideration the safety and efficiency of the National Airspace System. Imposing a curfew at one airport may benefit certain communities near that airport but may end up adversely impacting communities at destination or origin airports.
  • Where do your organizations stand on lowering to 55 dnl?
    • Any change to the 65 DNL threshold should be backed by science. That is why A4A supports the work FAA is doing to assess the DNL metric and the 65 dB threshold of significance. Further, the impacts associated with any changes to the DNL metric or threshold would need to be assessed prior to the change. Changing the noise significance threshold from 65 to 55 DNL could very well overwhelm FAA resources to review new Part 150 studies and disburse funds to sound insulation programs across the country as significantly more buildings would fall within qualifying neighborhoods. This change could result in delays in sound insulation program implementation as the same FAA staff would have increased workloads, and more communities would be vying for the same pool of money. Further, if such a change were to be made, land use restrictions should be required and enforced to prevent encroachment into areas where noise exposure has been reduced by the airlines or otherwise through sound insulation. The lack of land use controls has greatly undermined the aircraft noise reduction we have achieved to date.

Assessing Health Effects of Noise and Emissions:

Truls Gjestland:
  • What motivated you to look at the WHO data?
    • Simply curiosity. When I saw such an enormous change in the recommended levels, I wanted to find out the reason for this. And the answer was simply: there was no need for change. WHO has acted on the basis of results from a non-representative set of non-standardized surveys .
  • People experience noise cumulatively. When recommending exposure levels for health reasons, do you account for the contribution of all sources
    • I think the assumption that people experience noise cumulatively is incorrect. People experience separate noise events, and the annoyance response “just happens” to correlate with the cumulative noise level (as do a number of other things). But people can distinguish between sources. When asked about aircraft noise, they respond to aircraft noise more or less regardless of other sources. So, the background noise, i.e. noise from all other sources but aircraft, does not affect the annoyance assessment.
  • Did you measure the impact of the number of unique events for each given DNL?
    • My analysis was based on results from a number of previously published survey results. I have found that the number of noise events (per day) does make a difference.At equal DNL the annoyance is increasing with an increasing number of aircraft movements. So it seems better (less annoying)  to be exposed to a few very loud events instead of being exposed to a number of low-noise events during the whole day.
  • How are children and vulnerable populations reflected in the surveys? Or the various statistics to describe noise for regulatory decisions. 
    • The surveys usually address “a community”. Analyses have shown that about 300 respondents are sufficient to generate a “community response” Regulatory limits are usually defined (at least in Europe) at a 10 % level, i.e. it is accepted that 10% of a  community will be highly annoyed. The vulnerable groups are included in this 10 % portion of the community.
  • How was aircraft frequency and duration of noise addressed in the studies? These are major factors given Nextgen.
    • Most surveys rely on a very simple description of the noise exposure, the cumulative day-night equivalent level. If “aircraft frequency” refers to how often you experience a noise event, see the comment above. More flights means more annoyance, even if the DNL level remains constant.

Non-acoustic Factors in Aircraft Noise Impacts:

Sanford Fidell:
  • How have historical events, such as September 11th, changed annoyance levels with overhead aircraft noise? 
    • One can only speculate.  No research was conducted at a representative sample of U.S. airports of the prevalence of aircraft noise-induced annoyance immediately before and after the unanticipated event.  Even if a longitudinal study had been undertaken at intervals before and after the events of 9/11, how could the cause(s) of any observed differences at various points in time before and after 9/11 be attributed uniquely to 9/11?  Lacking any empirical basis, one person’s speculation is as good as another’s.
  • Furthermore, how should we counsel community members knowing the stimulus of overhead aircraft noise may cause PTSD, stress, and anxiety?
    • The question assumes its conclusions.  How is it known that residential aircraft noise “may cause PTSD?”  In whom, after what latent period, for how long, to what degree, for how long, etc.  “May cause PTSD, stress, and anxiety” is no more a defensible rationale for advising the community at large than “May not cause PTSD, stress, and anxiety.”
  • CTL is just a special case of more superior regression models (non-linear mixed effects). Why restrict yourself?
    • CTL is not a special case of regression modeling, nor is (for example) multi-level logistic regression modeling an obviously superior approach to predicting the prevalence of noise-induced annoyance.  Whereas regression fits a two-parameter (slope and intercept) curve to a data set, CTL analysis assumes a fixed slope, and uses a variable intercept to find a maximum likelihood fit of a data set to a pre-specified annoyance growth function.  In other words, rather than deriving a dosage-response relationship between noise exposure and the prevalence of annoyance in communities via a generic curve fitting procedure without an intrinsic causal rationale, CTL analysis fits a more parsimonious causal model to a set of field observations.  
    • The underlying causal assumptions of CTL analysis are 1) that dose-driven annoyance is caused by the effective (duration-adjusted) loudness of noise exposure, and 2) any observed deviations from the assumed rate of growth of loudness with exposure are attributable to the aggregate influences on annoyance judgments of non-acoustic factors.  Note that for all practical purposes, it is only the aggregate effects of non-acoustic influences on annoyance that are of interest in any event, since individual non-acoustic influences on annoyance judgments play no systematic role in aviation noise regulatory policy. 
    • Unlike logistic regression (in which the slope of the fitting function in a given community is a free parameter), CTL analysis thus assumes that the rate of growth of the prevalence of annoyance with sound exposure is fixed and invariant across communities.  The effective loudness of exposure, in turn, is assumed on the basis of widely accepted psychoacoustic research to grow as the 0.3 power of exposure.  CTL analysis thus attributes all observed deviations from the assumed growth rate of annoyance in different communities to differences in the value of the intercept of the fitting function. 
    • Reliance on the CTL approach is not a restriction – it is an example of the difference between understanding and scientific reasoning on the one hand, and acceptance of non-explanatory statistical observations that capitalize on chance on the other hand.
  • What are your thoughts about the impact of frequency of flights and duration of sound to the metric today and changes in the future?
    • The difficulty of predicting community response to aircraft noise exposure is not due to inadequate noise metrics, but to a paucity of genuine understanding of the multiple causes of adverse reactions to noise exposure.  All reasonable noise metrics correlate highly with Day-Night Average Sound Level, because DNL takes into consideration all of the physical parameters (level, duration, and number of noise events) that can plausibly contribute to annoyance.  Most non-DNL metrics differ from DNL only by scale factors and/or constants.
  • What are your thoughts about using machine learning to predict when folks will complain or express they are highly annoyed?
    • Machine learning is no more a panacea for the predicting the complexity of human attitudinal and behavioral reactions than any other technique.  As applied to prediction of individual aircraft noise-induced annoyance and complaints, it would require an enormous (and non-existent) set of training cases, and would not, even if more successful than other predictive approaches, provide an explanation of complaint behavior and annoyance.
  • Is the change in noise exposure is more important than the absolute DNL? Isn't this why the Metroplex projects have generated such negative reactions.
    • Very little is known quantitatively about the time constants of arousal and decay of aircraft-noise induced annoyance (how long it takes after increases in noise exposure before the prevalence of annoyance increases noticeably, and how long it takes after decreases in aircraft noise exposure for the prevalence of annoyance to dissipate.)  It is also not known to what degree  adverse reactions to changes in Metroplex are due exclusively to changes in noise exposure, or to other (non-acoustic) factors, including proximity to changed flight paths.

Air Traffic Noise and Emissions Management in practice

Samu Tuparinne:

  • Is 55 dB Lden the standard for Europe or specific to Finavia?
    • Lden 55 dB is applicable in all EU member states in processes that are required by the Environmental Noise Directive. Additionally, there can be other standards in use on the national level. In Finland, Lden 55 dB is also defined in national regulation.
  • What experience are you having with reduced power climb on takeoff up to 4000 ft?
    • The most effective solution as a noise abatement departure procedure varies case by case and depends on the location of the noise sensitive areas. Reduced power takeoffs may be used by operators also for purposes other than noise abatement. Typical NADP procedures just look at heights of thrust reduction or flap retraction and acceleration. ICAO suggests 3000 ft as a maximum height for noise abatement departure procedures. That’s why I don’t myself have any experience of procedures extended to heights higher than it.      
  • Have you received any pushback from pilots or ATC on the low power / low drag concept?
    • We are not yet in the operational deployment phase but discussing about the alternative means of deployment of the low power/low drag with the ANSP and major airlines. On this level pushback has not been received as they can also foresee the benefits.
  • Was the nighttime CDO performance better at night due to less traffic?
    • It’s likely the most significant contributor. During peak hours of the day time there are also independent approaches to parallel runways in use, reducing the day time CDO performance.
  • Who gets the money from nighttime noise charges? Is the money distributed to the residents most affected by ground based low frequency take off noise?
    • The night time noise charge is an airport charge among other charges. There are no processes in place to distribute it to residents.
  • What types of aircraft pose the greatest challenges and successes?
    • Probably the greatest challenges are caused by older widebodies that fortunately are not very frequently operating to Helsinki. A good example of the success potential is the new Airbus A350 that currently is the most operated widebody aircraft type at the airport. We are also looking forward to see A32s neos, B737 MAXes and similar to become more common.
  • Could you talk about feedback you are receiving from the community about the procedures?
    • Actually, we haven’t received much feedback from communities about individual procedures.
  • Do you get a lot of noise complaints despite all of the noise reduction efforts? Do you have a Noise Roundtable to address noise issues?
    • Typically we receive about 400-500 noise related contacts per year. Some people are happy to just receive more information to understand the situation. Some may continue complaining. There is no national framework defined for Noise Roundtables to formally discuss with the communities. 
  • Can you speak further to the areas where CDO has more benefits or not
    • In terms of reduced CO2 and fuel, CDO has benefits all the way from the top of descent. In terms of noise, CDO alone is most effective at areas far before the final approach fix, even 10 NM from the threshold and beyond. But in combination with low power / low drag, benefits can be reached also at the area of 4-10 NM to threshold. 
  • Is there much push back from airlines for use of quieter aircraft at nighttime?
    • I’m not aware of any significant pushback. There are no strict operating restrictions in place that is a benefit for the airlines. The best way to avoid any such restrictions in the future is to do what can be done to minimize the noise impact. 

Rachel Burbidge:  

  • How long has this program been going on?
    • The European CCO / CDO Task Force was established in 2015
  • Could you describe the stakeholders on the task force?
    • The two key stakeholders vital for the success of CCO / CDO are the airlines / pilots and the ANSPs / ATCOs. The stakeholders on the Task Force also include Industry Organisations e.g. ACI, CANSO and IATA together with Airports, regulatory authorities, Aircraft manufacturers, Research Organisations and the Network Manager
  • Are planes flying over different areas of the ground as a result of full implementation of CDO and CCO?
    • No, CCO and CDO should only affect the vertical profile
  • Can you explain what doing CDO actually looks like in practice what it requires of the pilot?
    • ​​​​​​​In practice, with no constraints in the sky, the pilot will identify his optimal top of descent point at which he will pull back the throttle and fly an idle descent down to approximately 3000ft. Of course, there are relatively few airports with no constraints. If the airspace has constraints, the ATCO and Pilot have to share information about the predicted trajectory of the flights so that the Pilot can plan his optimal most efficient descent profile. Even with a constraint, if the Pilot has sufficient information about the constraint, an efficient descent profile can be flown.
  • To what extent are flights in the US (or Europe) capable of achieving the sound benefits of CDO for aircraft flying below 7000’?
    • ​​​​​​​In the authors opinion, CDO below approximately 7000ft (where noise is considered the primary environmental impact) is already highly optimized at most airports, meaning that, in general, there are few additional benefits that can be gained, that is why we promote the optimization of CDO from top of descent.
  • What does EUROCONTROL do for steeper arrivals?
    • Business aviation aircraft flying steeper arrival profiles can still fly CDO as it is simply a pilot technique. Such aircraft typically fly faster and higher than commercial aircraft and usually start descent at a later point than other aircraft as most business jets have a lower Lift / Drag ratio and lower flight idle thrust compared to commercial jets. Business aviation aircraft usually fly into specific business aviation-oriented airports e.g. Paris Le Bourget, Nice. The European CCO / CDO Task Force encourages airspace design and the creation of coordination points and airspace constraints to be based on the fleet mix that fly to a specific airport. Nevertheless, where such airports are located in busy TMAs, the airspace design will have to take into consideration the different traffic flows and fleet mixes flying to the different airports. In Europe, complementary metrics for shallower aircraft profiles are also being studied.
  • Can you share more about CDO in congested airspace?
    • ​​​​​​​​​​​​​​The possibility for CDO in congested airspace is not a myth. The European CCO / CDO Action Plan provides a case study of CDO implementation at one of the biggest European airports, in core European airspace, from top of descent. Low level CDO where the focus is more on noise benefits has also been implemented to a high extent at core European airports.

Aircraft Operation Strategies for Reducing Noise and Emissions Impacts:

Melinda Pagilarello:
  • Why is United taking so long to retrofit A320 vortex generators. All planes have been in for significant maintenance yet many are not?
    • The aircraft are required to go through “heavy” maintenance, not the “significant” maintenance that occurs on a more frequent basis. Heavy maintenance is more like an overhaul where the fuel tanks are emptied. The modification requires the fuel tanks to be empty to fasten the VG’s to the wing. We are doing the modifications at every heavy maintenance event. As an aside, this schedule may be disrupted by the COVID-19 impacts.
  • Are the Noise Abatement Departure Procedures that you're developing at SNA applicable to other airports as well?
    • The procedure being tested is the basic NADP1 (sometimes referred to as close in) procedure authorized by FAA.
  • If you are truly concerned about noise at highly noise sensitive airports, why don't all of your departures use nadp1?
    • NADP1 procedures typically burn slightly more fuel and consequently, produce more emissions and are slower when climbing to 3000 feet. The slower speed may also reduce runway capacity. NADP2 is our standard takeoff profile. It is an airport’s prerogative to request the use of NADP1, however quantifying the benefits is complex because it requires detailed noise modeling and varies by aircraft type and the location of noise sensitive areas. In addition, NADP1 profiles are not standardized among the operators.
  • Can you elaborate on the NADP variation you are trialing?
    • We have demonstrated the profile with different altitudes for setting climb thrust. The FAA established a minimum altitude of 800 feet for thrust reduction. At locations where we do use NADP1, we typically reduce to climb thrust at 1500 feet.
  • You described a collaborative process at SFO but to date those meetings haven't included the community. How can communities become more involved in the process?
    • Collaboration can be facilitated through the Roundtable, FAA, or airport.
  • Are you involved with the GBAS project at SFO, if yes how do you envision it as regards noise?
    • United was a primary proponent of the project with the airport. We are optimistic that the system will contribute to noise reduction in the future
  • With the noise-reducing vortex generators, have you found a way to express the financial/non-financial business case that would help justify the costs?
    • There was no formal business case as there are no financial benefits. The project was undertaken purely to reduce the well documented community noise impacts associated with this aircraft. The cost of the modification is very modest, particularly since it is only done when the aircraft is taken out of service for an extended maintenance process.

Kallie Glover:

  • It's great that Delta removed the MD-88s from LGA, but what about the residents around other busier airports? Why don't they get a break?
    • Our May 2020 schedule shows the MD-88s operating to 20 stations; this number will continue to decrease as more MD-88s are retired. Delta has announced that all MD88 airplanes will be retired by the end of 2020.
  • Will Delta commit, like Jet Blue did, to install Vortex Generators on their entire A320 series fleet, during regular maintenance when cost effective?
    • Today nearly 60% of our Airbus narrowbody fleet (A319, 320, 321) are equipped with vortex generators. A320 family aircraft manufactured after March 2014 have the equipment installed.
    • We began taking delivery of the A320-200s in 1990, so as our older aircraft in the fleet approach 30 years old, there might not be enough useful life left to make the mod worth it.
  • New planes are efficient so arrivals are shallower, requiring more drag to slow down. What objective evidence do you have that new planes are quieter on arrivals?
    • As a correction to the question, generally all airline airplanes, new or old, actually fly a final approach flight path of approximately 3 degree slope to the runway. Some airports like SNA and SAN publish the readings from their Noise Monitors and distribute to us for review. Also, the FAA noise certification Approach level provides an objective quantitative measurement that demonstrates that newer designed airplanes are quieter on arrival.
  • Does your airline use similar procedures employed at John Wayne airport at other airports? If not, why?
    • Delta’s default standard departure procedure is an NADP-2 procedure.  Delta developed its NADP-2 procedure to achieve a balance of noise reduction, emissions reduction, safety, and air traffic capacity.  When the noise situation at a runway indicates that NADP-1 would be more beneficial than NADP-2,  Delta will fly an NADP-1 procedure.  This would occur when officially requested through the airport and FAA (generally as part of the quantitative Part 150 analysis process) .
  • Could you talk about your airline's participation in community collaboration forums?
    • ​​​​​​​We participate in a roundtable with other airlines at SNA. We participate in technical committees at FLL and SAN, as they are amending their Part 150 study. There is more community involvement that is done by other Delta groups; I’ve reached out for details and will get that information to you shortly
  • How many MD 88 does Delta still have in service?
    • There are 32 MD-88s still in service per our Aircraft Fleet Summary, effective 4/1/20. However, with reducing our fleet size by parking aircraft due to COVID-19, we will be accelerating retirements of older aircraft including MD-88’s.

Veronica Bradley:

  • The goal of reducing the number of people impacted by noise must also consider how intensely the still impacted people are affected. Please comment.
    • By way of background, FAA does assess the degree of noise exposure and changes to such exposure at multiple DNL contours, from 45 DNL to 65 DNL. Also, we support the work FAA is doing to further study and assess noise metrics. Despite the results of such assessments, A4A recognizes that while U.S. airlines have reduced the number of people exposed to significant noise by 94% since 1975 despite a quadrupling in enplanements, any particular person exposed to aircraft noise may have a negative experience. That is why we and our members work closely with FAA, aircraft manufacturers, and others in the industry to advance research, development, and deployment of technologies that reduce aircraft noise at the source; the primary means to reduce aircraft noise exposure. U.S. airlines have invested billions of dollars into upgrading their fleets, which contributes significantly to reducing noise exposure as today’s new aircraft are 50% quieter than aircraft 10 years ago. In addition, our airlines employ operating procedures to improve their noise impact for individual flights where and when achievable.

Aviation Emission Reduction Efforts:

Chris Dorbain:
  • Smaller general aviation aircraft still run on leaded AvGas. Neighbors of airports demand stop “spraying lead”. Can PAFI push to approve Shell’s “102 No Lead”?
    • Similar to next question
  • Residents near general aviation airports are concerned about lead in AvGas. Has there been any progress in finding an alternative fuel for those aircraft by the FAA?
  • Due to the unintended consequences of metroplex, why doesn't the FAA put a temporary hold on further implementation of the remaining planned metroplexes?
    • Outside of session scope
  • Do you have an update on what I believe is Project 18 which may include altitude thresholds for particulates? Follow up to Professor Barret’s study?
  • What phase of the landing/takeoff cycle does the CLEEN program technology tend to improve emissions for the most?
    • NOx emissions reductions for CLEEN are measured relative to the ICAO CAEP/8 standard. Information on how that certification standard is measured and computed can be found in Annex 16, Volume II.

Climate Change and Aviation:

Ralph Redman:
  • Have there already been or how many major flood events have already occurred at SAN? How were those events managed? [Answered Live]
    • Only major flooding events have occurred off-airport, some in close proximity to airport. These events are managed by others local agencies.  
  • The stormwater cistern would double as possible mitigation for sea level rise events? Would you need to desalinate and does that impact your space constraints? [Answered Live]
    • No, cisterns engineered to only catch stormwater runoff. Backflow events from the Bay would be managed and prevented from entering the actual cisterns. Desalination is not anticipated to be necessary.  All stormwater infrastructure is located underground but reuse of areas above cisterns is limited​​​​​​​
Melinda Franklin:
  • Has United also invested in AltAir fuel production?
    • United is only a SAF purchaser from World Energy Paramount (formerly AltAir Fuels) and does not own any share of the facility.
  • If SAF were to be sufficient quantities to necessitate storage, does SAF degrade when stored?
    • SAF needs to be blended with conventional jet fuel to be certified for use, at which point the two are indistinguishable. As a result, it would be impossible to tell if the SAF had degraded or the conventional fuel.
    • SAF is fuel that comes with a price premium, so the objective is to ensure that it’s used, not stored for a long period of time.