To measure operational inefficiencies, the ICAO GANP proposes a set of indicators:
These indicators compare the observed (actual) movement duration, e.g. from off-block to take-off, with an associated reference time. Reference times are calculated for flights with similar characteristics. From each sub-population the 20th percentile of the observed movement durations is calculated as the reference time.
Note: provide details to the algorithms.
From an environmental perspective, fuel burn is directly linked to engine time. Accordingly, inefficiencies, i.e. additional times, represent excessive engine time (and associated fuel burn). Green-house gas emissions are a product of fuel burn. Thus estimating the fuel burn per flight phase or measured inefficiency allows to quantify the environmental impact.
Fuel burn estimation requires a mapping of engine and airframe. This mapping is further complicated by the fact that various aircraft of the same family may be fitted with different engines. Accordingly, this work is not - yet - aiming to establish a “perfect” aircraft/engine mapping. The associated mapping is based on representative engines (and based on open data / resources).
taxi at uniform thrust setting / velocity - associated fuel consumption of aircraft \(F_i\) is as follows: \(F_i = T_i × f_i × N_i\) Ti is the taxiing time of aircraft i, fi is the fuel flow of one aircraft i, and Ni is the number of engines in aircraft i
The calculation formula of pollutant k is as follows: \(E_{ik} = T_i × f_i × N_i × EI_{ik}\) where Eik is the emissions of pollutant k of aircraft i during surface taxiing and EIik is the emission index of pollutant k from one engine of aircraft i.
The following builds on the formulation of Zhang et al., 2019 (zhangAssessmentMethodFuel2019a?).
where j represents the engine states, namely, idling, uniform velocity, breakaway, and turning; T E ij is the taxiing time of aircraft i under full-engine taxiing when the engine is at state j; Ni refers to the number of engines in aircraft i; fij is the fuel flow of aircraft i when the engine is at state j; and α refers to the influencing coefficient of low-visibility weather on taxiing time. Pollutant gas emissions of aircrafts are related to fuel consumption and states of the dynamic device. The emissions of pollutant k (E E ik) of aircraft i under full-engine taxiing can be expressed as follows: E E ik = X j T E ij × Ni × fij × α × EIijk, (9) where EIijk is the emission index of pollutant k of the aircraft i when the engine is at state j. (2) Single-engine taxiing. If frictional force and airport surface slope are allowed, then the aircraft can reserve one engine during taxiing. Under single-engine taxiing, the engine can only consume fuel and produce pollutants during its operation. If single-engine taxiing is adopted, then the main engine, which is closed, must be preheated before entering into the runway. The main engine can provide take-off power to the aircraft only after preheating. The engine start-up time (ESUT) is related to the aircraft mode, engine mode, and closed time of the engines. The duration is generally 2–5 min. Under taxiing, the aircraft needs time to cool the engines, which are closed during taxiing, after it lands. The engine cool-down time is similar to ESUT. The fuel consumption (F s i ) of any aircraft i under single taxiing can be expressed as follows: F s i = X j T s ij × Ni 2 × fij × α + Ni 2 × f 0 i × min T s i × α, 5 , (10) where T s ij is the taxiing time of aircraft i under single-engine taxiing when the engine is at state j; Ni 2 indicates aircraft taxiing when only half of the engines are started to produce thrust; fij is the fuel flow of aircraft i when the engine is at state j; f 0 i is the fuel flow under idling when preheating or cooling of engines is not needed during taxiing; min T s i × α, 5 indicates that if the taxiing time of the aircraft is longer than 5 min, then the preheating or cooling time of engines is set to 5 min. If the taxiing time is less than 5 min, then the preheating or cooling time of engines is used as the taxiing time. Under single-engine taxiing, emissions of pollutant k (E s ik) can be expressed as follows: E s ik = X j T s ij × Ni 2 × fij × α × EIijk + Ni 2 × f 0 i × min T s i × α, 5 × EIik, (11) where EIijk is the emission index of pollutant k of aircraft i when the engine is at state j and EIik is the emission index of pollutant k when the engine is at idling state. (3) External AGPS External AGPS is a taxiing mode driven by a motor tractor while the main engine of the aircraft is unused. When the tractor drags the aircraft to initiate surface taxiing, engines remain at the idling state and are only started 5 min before take-off. Later, the aircraft accomplishes taxiing in the last taxiway section, and the tractor automatically returns. The traction taxiing velocity of the aircraft is far smaller than that driven by engines. The tractor can be divided into diesel- and electric-driven types [36]. The latter is more economical and environmentally friendly than the former. However, comparing the electricity with fuel consumption under other taxiing modes is difficult. Therefore, the diesel-driven tractor was applied as an external AGPS in the present study. The fuel consumption (F t i ) of any aircraft i during external AGPS in an airport can be expressed as follows: F t i = Ti × BHP × LF × f t ij × α + Ni × f 0 i × min(Ti × α, 5) (12) where Ti is the surface taxiing time of aircraft i under external AGPS. Brake horsepower (BHP) refers to the average rated BHP of an engine equipment type
introduce LTO and modelling assumptions –> “aircraft engine exhaust emissions … (Masiol and Harrison)”.
ICAO defined a default LTO cycle consisting of distinct phases: takeoff, climb, approach, and taxi/ground idle. These phases are characterised with specified thrust levels and times-in-mode.
For our study we developed a lookup table for aircraft/representative engines and linked this to the ICAO Engine Databank (ICAO (n.d.)).
For taxi-in, we only apply the assumed 7% thrust setting of the Engine Databank. Note: this does not take into account reverse thrust operations to decelerate the aircraft during its landing roll.
For operational performance benchmarking the taxi-out measure is determined by deriving the taxi time as the difference between the actual off-block time (AOBT) and the actual take-off time (ATOT). This includes the take-off roll. The ICAO LTO time-in-mode assume a 0.7min (=42 sec) take-off roll. From an operational perspective this is a reasonable assumption for the majority of commercial aircraft.
Note: The take-off roll assumption needs to be adapted for piston and private aircraft operations (e.g. C172).