Methodology

The various methodologies used to extract flight lists, flight events and measurements from trajectory state vectors.

Flight List

To construct the flight list the trajectory needs to be identified from the state vectors. In addition, one needs to assign the Aerodrome of Departure (ADEP) and Aerodrome of Destination (ADES). Based on the state vector source, the trajectory might already contain an identifier id and an ADEP and ADES. The various subsequent algorithms are considered iterative improvements.

Version Improvements Release date Methodology
v0.0.1 Initial flight, ADEP and ADES identification algorithm. 1 November 2023 Link

Flight List Methodology

Object: Flight list

Version tag: flight_list_v0.0.1

Data source(s): OpenSky Network (OSN)

Flight identification algorithm(s):

Given the OSN state vectors, identifiers or ids are assigned in monthly batches. The statevectors are grouped per icao24 and callsign value. Each group is subsequently split and assigned a splitnumber if it is detected that there is a gap in between subsequent state vectors larger than 30 minutes or if there is a gap of 10 minutes whilst the altitude is below 1km.

The resulting trajectories are given ids which consist of the SHA256 value of the icao24 and callsign followed by the splitnumber and the year and month of the event_time. This is done to ensure uniqueness of the id.

ADEP/ADES identification algorithm(s):

To approximate the ADEP or ADES of a departing or arriving flight, coordinate grids are calculated for each airport with a radius of 10 km and a latitude/longitude step of 0.0001 degrees. For each point in the circular grid surrounding the airport, the distance to the Aerodrome Reference Point (ARP) is calculated.

The trajectories identified in the previous step are filtered to only retain state vectors with an altitude lower than 10,000 ft. Onto the latitude and longitude (rounded to 0.0001 degrees) of the remaining state vectors the airport coordinate grids are superimposed. Each state vector in the resulting data sets now indicates the various aerodromes the coordinates overlap with. If there are multiple aerodromes available, the minimal initial/final distance to the aerodrome indicates the most likely ADEP or ADES.

Flight Events

The flight events are extracted from the identified trajectories using different methods for the different types of flight events.

Version Improvements Release date Methodology
v0.0.1 Initial flight event extraction algorithm. 1 November 2023 Link

Flight Events Methodology

Object: Flight Events

Version tag: flight_events_v0.0.1

Data source(s): OSN

Flight event type(s):

Currently the following flight event types are extracted:

Event type Description
level-start The start of a level segment.
level-end The end of a level segment.
top-of-descent The top-of-descent.
top-of-climb The top-of-climb.
take-off The take-off.
landing The landing.
first-xing-fl50/70/100/245 The first crossing of the flight level (FL) 50/70/100/245 during flight.
last-xing-fl50/70/100/245 The last crossing of the flight level (FL) 50/70/100/245 during flight.

Flight event algorithm(s):

Phase derivations

Using OpenAP - The Open Model for Aircraft Performance and Emissions by Dr. Junzi Sun of the TU Delft, the state vectors of each flight were assessed and classified into various phases (GR = Ground phase, LVL = Level segment phase, CR = Cruise phase, DE = Descent phase, CL = Climb phase). Using this the events are identified in each flight as follows:

  • level-start: The first state vector in each level segment phase (LVL).
  • level-end: The last state vector in each level segment phase (LVL).
  • top-of-climb: The first state vector of the first cruise phase (CR).
  • top-of-descent: The last state vector of the last cruise phase (CR).
  • take-off: The first state vector of the climb phase (CL) after a ground phase (GND).
  • landing: The first state vector of the ground phase (GND) after a descent phase (DE).

Crossings

For each crossing of the respective flight levels (FL50/70/100/245) the algorithm is as follows:

  1. A smooth average flight level is calculated for each state vector.
  2. The flight values are compared between each subsequent state vector.

The first time it crosses a flight level of interest, the crossing state vector is recorded as a first-xing event. The last time it crosses a flight level of interest, the crossing state vector is recorded as a last-xing event.

Measurements

Version Improvements Release date Methodology
v0.0.1 Initial measurement calculation algorithm. 1 November 2023 Link

Measurement Methodology

Object: Measurements

Version tag: measurements_v0.0.1

Data source(s): OpenSky Network (OSN)

Measurement type(s):

Currently the following measurements are determined:

Measurement type Description
Distance Flown (NM) The cumulative distance flown up until this this event since the aircraft started its’ trajectory (at time first_seen).

Measurement algorithm(s):

Distance Flown (NM)

The Distance flown (NM) is calculated between each subsequent state vector using the great circle distance. The unit is nautic miles (NM). This segment distance is then summed cumulatively for each state vector since the first state vector (at time first_seen). This determined flown distance in nautic miles is then taken as measurement when identifying a flight event.

List of Acronyms

ADEP
Aerodrome of Departure
ADES
Aerodrome of Destination
ARP
Aerodrome Reference Point
OSN
OpenSky Network