Overview

This tool analyses the “Mayfly” document that is regularly released by Bristol Airport to calculate the probabilities of various levels of conflicting traffic for your arrival.

Conflicting traffic is considered to be traffic that arrives within ±5 minutes of your arrival time.

Input

Enter the flight number of your inbound sector(s) in the text box — use a space to separate multiple flight numbers — then click “Analyse”.

If you are running very behind schedule, your new projected arrival time may fall beyond the range of the calculation. In this case, you can move the range forward in time by adding a + and the number of minutes projected delay to the flight number, e.g. ezy1234+90 for a 90 minute projected delay. This procedure will also be necessary to find your flight if you are running the calculation after your scheduled arrival time; the algorithm finds your flight details by finding the first future arrival with the provided flight number.

Output

Each column of the “Probabilities” table gives the probability of a given quantity of aircraft conflicting with your arrival; for example the “≥2” column gives the probability that you will encounter two or more conflicting aircraft.

The rows of the “Probabilities” table are your own predicted delay, i.e. if you were running 10 minutes behind schedule, you would use the “10” row.

The “Arrivals considered” table shows the list of all arrivals that were considered for the calculation. Each row of the table considers a subset of this list.

Limitations

• The source data is a static document that is generally released a week or two before coming into effect. It is rarely updated after release. Unpublished changes to the schedule and/or unscheduled GA traffic will not be included in the analysis. That said, comparison with the arrivals board shows that the Mayfly is generally correct.
• Delays are assumed to be independent. Events simultaneously causing delays to multiple inbound aircraft render the calculation void.
• No account is taken of what is actually happening on the day: if a flight is cancelled, for example, it will still be considered by the analysis.
• No account is taken of the effect of departures.

Tips

• If running the calculation of your company iPad, you can share the result with the “Books” app by clicking the square icon with the up arrow. This gives you access to the results when not connected to the Internet.
• The same menu also has an “Add to Home Screen“ option if you scroll down. This will allow you to drop a shortcut on to the main iPad screen for quick access if you should so desire.

Methodology

The tool works by applying a cumulative distribution function, derived from an analysis of historic inbound delays, to Bristol arrivals in order to determine the probability that they will arrive within a given 10 minute window. These probabilities are then combined to give the probabilities of various quantities of aircraft arriving within that window. This is essentially a binomial distribution, but with different probabilities for each event.

These probabilities are presented as columns in a table, having first been transformed into the probability of encountering greater than or equal to a given number of arrivals. A series of consecutive 10 minute windows around your own scheduled arrival time are calculated and presented as rows of this table in order to be able to account for your own delay.