Guide

Will my flight be delayed?

Airlines usually announce a delay once they know the new departure time. You can often see it coming earlier by looking at the same things the airline is looking at, starting with the plane that is flying in to operate your flight.

Why the board still says on time

A departures board shows the airline's official status for that airport. It changes when the airline sets a new time, not when a problem first appears. So a flight can show as on time while the plane that will operate it is still in the air somewhere else, running late.

That doesn't mean anyone is hiding anything. The airline may still hope to make up the time, swap planes or shorten the turnaround. But for you, it means the board is a record of decisions already made, not a forecast.

Sign 1: where the incoming plane is

Most flights are operated by a plane that first has to fly in to your airport. If that incoming flight is late, or is due to land shortly before your departure, your flight is likely to leave late as well. This is the single most useful thing to check, and you can often see it before the airline announces anything. Our guide on where your plane is coming from explains how to find it.

Sign 2: how long the plane needs on the ground

Once it lands, a plane needs time to taxi to the gate, unload, be cleaned and refuelled, and board again. This turnaround varies by airline, aircraft and airport. A tight turnaround leaves no room for a late arrival; a generous one can absorb it. Knowing what is normal on your route tells you how much a late incoming plane really matters.

Sign 3: the flight's recent track record

Some flights are late day after day, often because they sit late in a plane's daily schedule, after several earlier legs. Looking at how the same flight did over the last few days gives useful context. It isn't a forecast for your day, but a flight that is usually late deserves a closer look.

Other things that cause delays

Many delays have causes you can't see from the plane's position:

• Weather at your airport, at the destination or along the way.
• Air traffic control restrictions, such as limits on how many flights can take off or land in an hour, which lead to departure slots.
• Busy airports, with queues for gates, stands or runways.
• Crew availability and working time limits.
• Technical checks or repairs on the aircraft.

Some of these show up indirectly, because they make the incoming plane late. Others only appear when the airline announces them.

What DelayAhead checks

• The flight's schedule, route and the airline's current status and times.
• Which plane is operating the flight, where we can identify it, and how sure we are.
• The plane's earlier flight into your departure airport and when it is expected to land.
• How long the plane usually needs on the ground on that route, from recent turnarounds where available.
• The flight's recent departure and arrival record, where verified times are available.

From these, we show a risk level (low, medium or high), the likely delay and the expected new departure and landing times, in local time at each airport.

What it can't know

We don't see the airline's operational decisions. We can't know about a crew problem, a technical fault or an air traffic control slot until it shows up in the flight data or the airline announces it. The airline may swap planes, and sometimes the aircraft isn't assigned until close to departure, in which case we tell you we haven't found the plane yet.

Official delay or our prediction?

Every result says which one you are looking at. An official airline delay means the airline has announced it. Our prediction, not announced yet means we expect a delay from the incoming plane, but the airline hasn't confirmed one. Plan around the airline's official times, and use our prediction as an early heads-up. Always check with your airline before you travel.