Airports are under growing pressure to meet Airport Carbon Accreditation requirements - particularly those targeting ACA Level 3 and Level 4, where documented operational improvements are mandatory - and with flight emissions representing over 90% of their total carbon footprint on average, how aircraft fly has become as critical as how airports are built and run.
Descent operations are one of the most concrete levers available, yet a significant share of arriving flights still include unnecessary level-offs, adding fuel burn, noise, and avoidable climate impact.
Having the data to measure and act on this is what turns a commitment into a real plan - and it opens the door to two areas where airports have real room to progress : strengthening the quality of emissions data that underpins their certification, and building partnerships with airlines and aviation authorities that serve all sides, turning a compliance requirement into a shared efficiency agenda.
This is exactly what we provide at Estuaire - descent profiles flight by flight - to give airports and airlines the visibility they need to reduce inefficiencies in descent operations and engage aviation authorities with concrete evidence.
What is a Continuous Descent Operation?
When an aircraft approaches an airport, the ideal profile is a smooth, uninterrupted descent from cruise altitude to touchdown. No flat segments, no holding at intermediate altitudes. This is called a Continuous Descent Operation (CDO).
The alternative – where a flight levels off at one or more altitudes before continuing its descent – is called a Non-Continuous Descent Operation (NCDO). These flat segments, or level-offs, are driven by air traffic control sequencing constraints within Standard Instrument Arrival (STAR) procedures: the aircraft is instructed to hold altitude while controllers manage the flow of traffic arriving at the airport.
The difference between the two profiles looks minor on a chart. In practice, it adds up.
The operational and climate cost
Fuel and emissions
Each level-off means the aircraft engine operates longer than necessary at a given thrust setting, resulting in a direct and measurable loss of fuel efficiency. Aggregated across hundreds of flights per day, the excess fuel burn is measurable. For airports working to track and reduce their Scope 3 emissions, which include the emissions of aircraft operating to and from their facilities, this data is directly relevant.
Noise
For airports operating in or near urban areas, noise is one of the most politically sensitive topics. Level-offs during final approach (below 6,000 feet) generate additional noise exposure for communities under the flight path, directly undermining Noise Abatement Procedures (NAP) that airports have committed to. Identifying where and how often these occur gives airports the evidence they need to engage constructively with airlines, ANSPs, and local authorities.
Certification and stakeholder pressure
Aviation authorities and local politics increasingly expect airports to demonstrate active management of their environmental performance. A systematic analysis of descent operations provides exactly the kind of structured, quantified evidence that supports engagement with ANSPs on procedural improvements, and that feeds into sustainability reports, Stakeholder Engagement Plans (SEP), Environmental Action Plans (EAP), and regulatory filings.
From Analysis to Action
The value of this analysis is not just in the numbers. It is in what airports can do with them.
Identify the patterns. Understanding which altitude bands concentrate the most level-offs, at what times of day, and under what traffic conditions gives airport operations teams a precise picture of where the system is underperforming.
Quantify the impact. Translating level-off frequency into fuel burn, emissions, and noise exposure turns an operational observation into a business and sustainability case.
Build an evidence base. Airports do not control ATC procedures. But they can influence them by bringing data to the table. A well-documented analysis of descent inefficiencies is a credible starting point for Airport Collaborative Decision Making (A-CDM) conversations with ANSPs about Performance-Based Navigation (PBN) procedure changes, performance targets, and continuous improvement programs.
Track progress over time. Running this analysis continuously – not as a one-off study – allows airports to measure whether interventions are working and to demonstrate improvement to stakeholders over time.
How we make it happen
Estuaire processes flight trajectory data at scale to produce structured, actionable analyses of airport operations. For descent efficiency, this means flight-by-flight classification of CDO and NCDO profiles, level-off detection and altitude mapping, fuel and noise impact quantification, and trend analysis over time.
The output is designed to be used directly by airport operations, sustainability, and regulatory affairs teams..
We work with airports across Europe and beyond. The analysis described in this article reflects findings that are broadly consistent across the airports in our portfolio, regardless of size or geography.
Practically, at Estuaire, we analyzed thousands of arrival flights at a major European airport over a one-month period. The findings are consistent with what we observe across the airports we work with.
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“Roughly 1 in 3 flights does not follow a continuous descent profile”
That means a significant share of arriving aircraft – around 30% – interrupt their descent with at least one level segment before landing. Some flights show multiple level-offs across different altitude bands.
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When we look at where these interruptions concentrate, two zones stand out:
- Between 2 000 and 6 000 feet: the final approach phase, close to the ground
- Around 30 000–34 000 feet: the early descent phase, just after top of descent
Level-offs in the final approach phase are particularly significant because of their noise impact: engines working at higher thrust settings at low altitude, directly over populated areas surrounding the airport. Level-offs at higher altitudes contribute primarily to excess fuel burn.
The inefficiencies follow repeatable patterns, concentrated in specific altitude bands, driven by identifiable operational constraints.
Conclusion
Continuous descent is not a new concept. It has been an industry objective for years. What is new is the ability to measure it systematically, at scale, and to turn that measurement into a structured program of improvement.
Airports working toward carbon neutral status, and those seeking to progress through Airport Carbon Accreditation (ACA) levels, need to start with the data. Descent operations are one of the clearest places to look.
If you want to understand what this analysis would show for your airport, we are happy to talk.
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- What does "top of descent" mean? Top of Descent (TOD) is the point in a flight where the aircraft begins its descent from cruise altitude toward the destination airport. It marks the start of the descent phase and is where continuous or non-continuous profiles begin to diverge.
- What is the difference between CDO and NCDO? CDO (Continuous Descent Operation) follows an uninterrupted descent profile. NCDO (Non-Continuous Descent Operation) includes one or more flat segments where the aircraft holds altitude before continuing its descent. NCDOs result in higher fuel consumption and greater noise exposure near the airport.
- Why do some flights include level-offs during descent? Level-offs are mostly driven by air traffic control sequencing constraints. When multiple aircraft are arriving at the same time, controllers may instruct a flight to hold at a given altitude to maintain safe separation.
- What is an ANSP? ANSP stands for Air Navigation Service Provider. These are the organizations responsible for managing air traffic in a given airspace. In Europe, examples include DSNA in France, NATS in the UK, or DFS in Germany. They are the key stakeholders when it comes to modifying descent procedures.
- What is Scope 3 in aviation, and why does it matter for airports? Scope 3 emissions cover indirect emissions from sources not owned or controlled by the reporting entity. For airports, this includes the aircraft operating to and from their facilities. As regulatory pressure increases, airports are expected to measure and report these emissions, making flight-level data increasingly important.
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