Arrival time on flight trackers: how accurate is the ETA for spotting?

The long-haul jet in the special livery lands at 2:52 p.m. according to the flight tracker. You plan calmly, arrive at the fence at 2:45 p.m. – and just see it disappearing behind the terminal. Or the other way around: you stand in the cold for an hour because the forecast keeps slipping back by five minutes. Both have the same cause: the arrival time on the flight tracker is an estimate, and its accuracy depends heavily on where the aircraft is right now and what exactly the time actually means. This guide explains how ETA forecasts come about, where their typical errors lie and how to factor them into your spotting day so that you don’t miss the target aircraft.

How accurate is the ETA? The short answer

As accurate as the phase of flight allows. Before departure the displayed arrival time is often little more than the flight plan. In cruise it becomes stable because position, speed and remaining distance are known. In the approach phase there is movement once more: air traffic control puts the arriving aircraft into a sequence, lengthens routes, slows aircraft down or sends them into a holding pattern. Only on final approach is the landing time practically fixed.

Add to that a misunderstanding that regularly costs spotters pictures: many times don’t refer to the landing at all but to arrival at the gate. Between touchdown and the parking position lie taxi routes that can be considerable at big airports. If you take a gate time for the landing time, you will systematically arrive too late.

Where the arrival time on the flight tracker comes from

An ETA (estimated time of arrival) is the result of a calculation, and every service calculates a little differently. The ingredients are similar everywhere, though:

• Flight plan and airline data: The scheduled arrival time comes from the airlines’ flight schedules, which tracking services receive long in advance. Before departure it is often the only basis.
• Live positions: As soon as the aircraft is flying, ADS-B receivers, multilateration and, depending on the region, satellite reception supply position, altitude and speed. How this works technically is explained in the guides on flight tracking with ADS-B and MLAT.
• Data from authorities and airports: Some services additionally obtain data from air traffic control, airports and airlines – such as actual takeoff and landing times or updated gate times.
• Models and historical data: Simple forecasts calculate from remaining distance and speed. More advanced methods include weather, airport conditions and historical patterns. FlightAware, for example, describes its forecasting system Foresight as a deep learning model that combines live positions, weather, airport conditions and schedule data and predicts a landing time and an arrival time at the gate separately.

For you that means: two services can show different times for the same flight without either being “wrong”. They use different sources and different models. Which apps are worthwhile for spotters is compared in the article flight tracker apps compared.

Landing or gate? The most important distinction

In air traffic there are several arrival times, and they are constantly mixed up:

Time	What happens	Where you see it	Relevance for spotters
Scheduled arrival	time per the flight plan, usually at the gate	booking, arrival board, flight tracker	only rough guidance
Estimated landing time	touchdown on the runway, forecast	some flight tracker services as a separate value	decisive for approach and landing photos
Actual landing	touchdown on the runway, measured	flight history, live map	for matching your photos
Estimated arrival at the gate	aircraft is at the parking position, forecast	arrival board, airline app	important for apron and terrace photos
Actual arrival at the gate	chocks in, “on-block”	arrival board, flight history	more for statistics

In its help pages FlightAware explicitly points out that airlines generally publish gate times and that gate and runway times can differ significantly at big airports because of taxi times and waiting on the ground. The airport’s arrival board also usually shows the expected arrival at the parking position. How to read these boards for your spotting day is covered in the guide using arrival and departure boards for spotting.

Where the forecast is off: the typical sources of error

The accuracy of an ETA depends less on the service than on what happens in the airspace. These factors most often shift the arrival:

Before departure: delayed takeoff

As long as the aircraft is on the ground, no service can know when it will actually take off. Delays from previous rotations, slot restrictions or problems during boarding feed straight through into the arrival time. The reasons are explained in the article why flights are delayed, and the logic behind takeoff and landing rights in the piece airport slots. For you that means: never plan based on a forecast for a flight that hasn’t departed yet.

In cruise: wind and routing

Headwinds and tailwinds at cruising altitude change ground speed, sometimes considerably, and on long-haul routes the flight duration as well. Detours around thunderstorm cells or closed airspace lengthen the route. Good models factor that in, while simple forecasts only notice when the speed changes in the live signal. In addition there are stretches without ground coverage, such as over the Atlantic: there the service sometimes only estimates the position when no satellite reception is available. More on this in the guide space-based ADS-B.

On approach: sequencing and holdings

This is where the most surprising jumps arise. When more aircraft arrive than the runways can handle, air traffic control spaces them out: it assigns speeds, lengthens the approach path with vectors or sends aircraft into a holding pattern. Each of these measures pushes the landing time back – often only after the forecast already looked “done”. How holding patterns work and how to spot them on the map is explained in holding: the holding pattern explained and spotting holdings on the flight tracker.

At the end: runway change and diversion

If the wind turns, the runway direction in use changes – and with it the approach path. An aircraft that now lands from the east instead of from the west needs a different, sometimes longer route. For you this is doubly relevant: not just the time, your spot can suddenly be wrong too. The basics are in the guide understanding runway direction in use at an airport. In the extreme case the aircraft doesn’t land at its destination at all; how to spot a diversion live is covered in a separate article.

Reliability by phase of flight

The following overview summarizes how you should rate the ETA depending on the phase of flight. The assessments are rules of thumb, not measurements from any particular service.

Phase of flight	Basis of the forecast	Reliability	What you should do
Before departure	flight plan, possibly airline updates	low	plan only roughly, wait for departure
Shortly after takeoff	takeoff time plus planned flight duration	medium	set your travel roughly
Cruise	position, speed, remaining distance	good, as long as wind and route are stable	set your departure time
Descent and approach	live data plus sequencing	fluctuating	watch the map, watch for holdings
Final approach	position on the approach baseline	very good	camera ready, check settings

The time delay of the data itself is also important. FlightAware states that the displayed data is typically about 30 seconds behind real time and that the position on the map can lag by up to one to two minutes. Other services work with their own delays, which differ by region and data source. On final approach, where a jet covers several kilometers in a minute, that is noticeable: the symbol on the map is already a bit of “the past”. What the individual symbols and data fields mean is explained in the guide flight tracker symbols and colors.

Big airports: where the forecast gets better

At many big European airports, airport operators, airlines, ground handlers and air traffic control work together under the Airport Collaborative Decision Making (A-CDM) procedure. According to EUROCONTROL it is fully implemented at around 35 European airports, including Frankfurt and Munich. The aim is for all parties to share the same up-to-date times – such as when an aircraft is ready for handling and when it can depart. This makes departures in particular more predictable, and the arrival forecast at the destination airport indirectly benefits from that too.

For spotters this doesn’t mean you see every time from these systems. But flights between big airports tend to have cleaner data than connections from small airfields with little coverage.

How to plan the arrival for your spot

With this knowledge, the ETA becomes a usable tool. The routine is always the same:

You can roughly estimate how much lead time you need:

Strategies for different spotting goals

Not every spotting day revolves around a single aircraft. How strictly you have to take the ETA depends on your goal.

For long-haul flights it is worth looking at the typical arrival waves: many connections from North America or Asia land in Europe in certain time windows. When the big waves come is described in the article when long-haul flights land in Europe, and how hubs bundle their arrivals in the guide on hub waves at hubs. At the Zeppelinheim viewing platform or the Munich Airport visitors’ hill you can catch a whole wave this way instead of betting on a single aircraft.

What to keep in mind

• Flight number is not aircraft. The same flight number can be flown by different aircraft on different days. The difference between callsign and flight number is explained in the guide callsign and flight number.
• Earlier is always possible. An ETA can also jump forward at the last moment, for example when air traffic control clears a shorter approach. Never arrive “to the minute”.
• Check time zones. Some services show times in the airport’s local time, others in UTC or in your device’s time zone. A wrong setting costs you an hour or two.
• Compare several sources. Flight tracker, arrival board and airline app often show slightly different values. If all three are close together, the forecast is reliable.
• Factor in the weather. Thunderstorms, fog or strong crosswinds slow down traffic and make forecasts jumpy. You can check wind and clouds in advance with Windy and other weather maps.
• Stay safe. If you rush to the spot at the last minute, you park wrongly or walk over paths that are off limits. What is allowed at the fence is covered in the article Is plane spotting allowed?.

Conclusion

The arrival time on the flight tracker is a tool with built-in fuzziness. Before departure it is little more than the flight plan, in cruise it becomes stable, on approach it wobbles once more, and only on final approach is it truly certain. Add to that the question of whether a time means the landing or arrival at the gate – for spotters a difference of decisive minutes. If you know this logic, you plan with the estimated landing time, factor in a fixed buffer and follow the last half hour live. Then the forecast becomes a reliable timetable for your spotting day. And if you note after every visit how far forecast and actual landing were apart, you will soon know your home airports better than any model. How to match your sightings with flight data after the fact is shown in the guide matching sightings with ADS-B logs.