Collaborative Air Traffic Flow Management - Page 1 of CDM Operation

Back in 2012, with the aim of proposing Air Traffic Flow Management (ATFM) service providers rational alternatives for the handling of highly congested airspaces, ICAO has published Doc. 9971 AN/485 (Collaborative Air Traffic Flow Management), which has been commonly referred to as CDM (Collaborative Decision Making) operation.

The so called Collaborative ATFM proposed by ICAO consisted of ATFM measures, adopted for balancing demand & capacity in different volumes of airspace and airport environments, under a fundamental principle:

“Whenever ATFM measures taken to manage traffic flows cause delays, ATC must notify airspace users, while aircraft are on the ground rather than in flight.”

The main tool proposed by ICAO to that end was the GDP (Ground Delay Program) measure, the objective of which was to ensure that flights, which would otherwise exceed the capacity of the integrated system (airspace/airports), should be held on the ground, to manage demand & capacity in specific volumes of airspace or airports. CTOTs (Calculated Takeoff Times) should be issued to such fights, to adjust them to the capacity of airspace congested sectors, avoiding delays and fuel waste associated with inflight holdings.

ICAO Doc. 9971 AN/485 highlighted that "exchange of information" was to be seen as facilitating element, but not sufficient, for Collaborative ATFM, which required predefined rules and processes to ensure quick and efficient decisions

Benefits

ICAO´s proposed Collaborative ATFM was designed to produce benefits in different areas:

CAPACITY

The Collaborative ATFM protects the maximum operating capacity of the integrated system by filtering excessive demand, preventing maximum capacity from being compromised. Similar to vehicle restriction adopted at critical times, in metropolises with large vehicle traffic.

Collaborative ATFM should protect, at a TACTICAL level, the maximum operational capacity of the system, based on STRATEGIC slots (for the season), by addressing imbalances caused by external factors (weather conditions, airport closures, etc.), before they reached Air Traffic Controllers´ OPERATIONAL initiatives (inflight holdings, large takeoff cues, etc.)

COST-BENEFIT

With a view to protect operations´ cost effectiveness, Collaborative ATFM offers airspace managers specific tools to choose between fuel savings and takeoff punctuality, similar to airlines´ Cost Index, which allow trade-off between flight time and fuel burn, when defining cruising speed of their flights.

EFFICIENCY

Search for maximum efficiency of gate-to-gate operations is the very essence of Collaborative ATFM, eliminating events such as inflight holdings and large takeoff cues, which in no case contribute to the overall punctuality of operations.

PREDICTABILITY

Collaborative ATFM ensures uninterrupted gate-to-gate operation, eliminating discontinuities in the operation and ensuring maximum predictability, recognizing air transport end users´ effective punctuality commitments are consolidated upon arrival at the destination, rather than on door-close, at origin.

Interferences with Airlines´ Flight Intentions

Collaborative ATFM proposed gradual introduction of interferences with airlines´ flight intentions, this being the main reason for its early rejection, at regions where:

• Traffic volume was not as critical as in Europe and United States
• Local culture was 100% focused on door-close punctuality, once Collaborative ATFM proposed a clear priority change, favoring fuel efficiency in detriment of door close punctuality

Collaborative ATFM - Commitments and Consequences

Highly accurate takeoff time estimates were the raw material of Collaborative ATFM, as it would be unfeasible to establish achievable inflight sequences (and calculate realistic CTOTs), based upon inaccurate ETDs (Estimated Times of Departure).

That explains why Collaborative ATFM adoption requires high predictability of the airports in the region, which is unrealistic at airports operating with low level of situational awareness (no surface surveillance information available) and/or with Air Traffic Controllers in charge of “efficiently moving” aircraft and vehicles in the Apron.

Collaborative ATFM, a success case !

Collaborative ATFM has been successfully adopted in Europe - ATFCM (Air Traffic Flow and Capacity Management) and United States - TBFM (Time Based Flow Management) - two different ATFM programs, which have effectively achieved reduction of airspace congestion.

Indeed, a fantastic antibiotic to treat the original infection - airspace congestion, despite its interference with airlines´ flight intentions.

Collaborative ATFM´s side effects

As antibiotics quite often produce side effects, airside management of airports in Europe and the United States have been affected by the assignment of CTOTs to specific flights, as start-up & pushback authorizations were managed by call order (first called, first served). All of a sudden, flights would reach holding point, prior to their assigned CTOTs, thus being required to await CTOT, blocking the takeoff sequence.

As traffic increased and so did the number of assigned CTOTs, Collaborative ATFM´s side effect has become unmanageable and the only solution was to pre-sequence start-up & pushback authorizations as well, to make them compatible with the CTOTs.

The expansion of Collaborative ATFM concept towards airside operation would further affect airlines´ flight intentions. Airlines would now receive, for each flight, a start-up & pushback authorization - TSAT (Target Star-up Approval Time) limited to a 10-minute tolerance time (-5/+5 min), which would be as achievable as the accuracy of their estimates for readiness - TOBT (Target Off-block Time).

That was the price to pay for overcoming the effect of CTOTs at takeoff cues !  

Eurocontrol and FAA approaches

With a view to achieve the level of airside situation awareness required to cope with the enforcement of TOBT/TSAT, Eurocontrol and the FAA proposed different alternatives to airports willing to integrate with their Collaborative ATFM services.

Eurocontrol designed A-CDM (Airport CDM) - an “Assembly Line” type of algorithm, connecting 16 events, from 3-hours before EOBT (Estimated Off-Block Time) until actual takeoff time of each flight (the 16-Milestone Approach) and an IT platform managed by each airport operator ACISP, (A-CDM Common Information Sharing Platform), which the various stakeholders should feed, in real time, as each flight reached each of the 16 events (Milestones).

The FAA proposed S-CDM (Surface CDM), adopting as key element for promoting airside situational awareness, real time access to surface surveillance data by all stakeholders, inspired by ICAO GANP (Global Air Navigation Plan) ASBU-B0/2 (Comprehensive Situation Awareness of Surface Operations).

Conclusion

What is essential for airport stakeholders outside Europe and United States to understand is that A-CDM (Airport CDM) and S-CDM (Surface CDM) were designed to address the side effect of Collaborative ATFM adoption in Europe and United States.

One should not attempt to adopt a medicine for the liver, hoping to address the original infection - traffic demand exceeding airspace/airports integrated capacity.

Considering the adoption of A-CDM or S-CDM without having understood, accepted and adopted Collaborative AFM - and that includes its commitments and consequences, denotes lack of knowledge and has already produced enough operational chaos and financial losses at developing regions.