Spotting a diversion live: turning alternate landings into a spotter opportunity

Dense fog lies over the hub, on the live map three long-haul jets draw their ovals over the surrounding area – and half an hour later an aircraft touches down at your small home airport that is otherwise never seen there. Moments like these are among the most exciting in the hobby. If you can spot a diversion live, you are at the fence in time when the alternate landing happens. This guide shows you the typical warning signs on flight tracker, weather map and arrivals board, explains how to estimate the likely alternate airport, and why consideration matters more than the perfect picture.

What a diversion is – the short answer

A diversion is a landing at an airport other than the planned destination. In technical language, three cases are distinguished: the return to the departure airport shortly after takeoff, the en-route diversion and the alternate landing near the destination when landing there is not possible. The decision rests with the captain, who relies on the airline and air traffic control.

The reasons are varied:

• Weather at the destination: fog below landing minima, thunderstorms over the approach, strong crosswind, snow or a flooded runway.
• Closed runway or airport: a disabled aircraft, construction work, a security incident or the end of operating hours.
• Problems on board: technical faults, a medical emergency, a disruptive passenger or too little fuel after long holding patterns.
• Airspace and clearances: closures or detours that upset the planning.

How alternate airports are selected during flight planning and what the crew weighs up is explained in detail in the article Diversion to an alternate airport. Here it is about practice: how you catch a diversion live and what it brings you as a spotter.

Why alternate airports are no coincidence

Every scheduled flight under instrument flight rules plans alternatives. The ICAO rules know three kinds of alternate airports for this: one for the case that a return to the departure airport is not possible shortly after takeoff, one or more along the route and one at the destination. The destination alternate is in the flight plan, and additional fuel is taken on board for it. It may only be dispensed with under narrowly defined conditions that concern, among other things, the expected weather and the available runways at the destination.

On long routes over water or sparsely populated areas, the EDTO rules come on top – the ICAO term that has replaced the better-known ETOPS and also includes aircraft with more than two engines. They apply when the flight time to a suitable alternate exceeds a set threshold, usually 60 minutes or a value set by the supervisory authority. These en-route alternates must, among other things, offer at least one approach aid and a minimum airport firefighting category. What these categories are about is in the article on Airport firefighting categories.

For you as a spotter, an important insight follows: not every airport can take every aircraft. An Airbus A380 needs a sufficiently long and wide runway, suitable firefighting equipment, stairs or jet bridges and an apron where it can even find room. That is why large long-haul jets on alternate landings typically end up at airports that at least occasionally see similarly large aircraft – not at the smallest field in the region.

A well-known example of an airport with an alternate role is Shannon on the Irish west coast. Thanks to its location at the edge of the Atlantic and with Ireland’s longest runway at about 3.2 kilometers, it has for decades taken stopovers from transatlantic flights, including unplanned ones.

The warning signs: how a diversion announces itself

An alternate landing seldom happens out of the blue. There are usually signals you can read long before the aircraft touches down at the other airport.

1. Holding patterns before the destination

The classic sign on the live map is holds: aircraft circling in ovals over fixed points. On their own they only mean that the approach is not currently possible without delay – for example because of heavy traffic, thunderstorms on the approach or a briefly closed runway. How to reliably recognize holds on the map is shown in the guide Recognizing holding patterns on the flight tracker; the procedures behind them are explained in the article Holding and holding patterns. It gets exciting when the loops stack up over a longer time. Every lap costs fuel, and at some point the moment comes when the crew has to turn away to the alternate to arrive there with sufficient reserve.

2. Course change away from the destination

If a flight turns away from the hold or the approach and heads for another airport, the diversion is usually decided. Watch direction, descent and speed: anyone descending markedly while heading for a neighboring airport wants to land there. The displayed destination, on the other hand, often stays at the original airport for a while on many flight tracking services, because it comes from the flight plan. Why data is sometimes delayed or patchy is explained in the article Why an aircraft doesn’t show up on Flightradar.

3. Status messages and arrivals boards

Many flight tracking services and airport websites mark diverted flights with notes such as “Diverted” or “umgeleitet” (German for diverted), often with the new destination airport. On the arrivals board of the original destination, affected flights disappear or get a corresponding note. How to read arrival and departure schedules for spotting planning is shown in the guide Using departure and arrivals boards.

4. The weather at the destination

Many diversions explain themselves as soon as you look at the current weather report of the destination airport. Fog with very low visibility, thunderstorm cells over the field, strong gusts across the runway or snowfall appear there in compact form. How to decode METAR and TAF is in the article Reading METAR and TAF. If the TAF shows a deterioration for the coming hours, you can foresee alternate landings before the first aircraft goes into the hold.

5. Emergency codes

When a crew sets the transponder code 7700, it is shown highlighted immediately on many flight tracking services. Not every diversion is an emergency and not every emergency ends in a diversion – but medical and technical cases often start this way. What the codes mean exactly is explained in the article Squawk codes 7500, 7600 and 7700.

Signal	Where you see it	What it means	Reliability
Holding patterns	Live map	Approach delayed, fuel getting tighter	Warning sign, no decision yet
Course change and descent toward another airport	Live map, altitude profile	Diversion usually decided	high
“Diverted” or “umgeleitet” (German for diverted)	Flight tracker status, arrivals board	official or derived status change	high, but often delayed
Fog, thunderstorms, crosswind in METAR or TAF	Weather services	Cause of possible waves of diversions	good for forecasting
Squawk 7700	Live map	Emergency on board	Indication of an emergency, not of severity

Estimating the likely alternate airport

As soon as you sense a diversion coming, the decisive question arises: where does the aircraft land? There is no reliable prediction, but you can narrow down the candidates.

• Distance and fuel: After long holding patterns, the crew will rather choose a nearby airport. Anyone who turns away early has more room to maneuver.
• Size of the aircraft: The bigger the type, the fewer airports come into question. A regional jet finds room almost anywhere, a Boeing 777-300ER only at fields with suitable infrastructure.
• Weather at the alternate: A widespread fog situation often affects several neighboring airports at the same time. Flights then divert to fields that are farther away but have better weather.
• Operating hours: Late in the evening, airports with night flight restrictions drop out. A flight that can no longer reach its destination once the delay rules have run out has to divert to an airport where night flying is allowed – such as Cologne/Bonn with its round-the-clock operations. The rules of the individual airports are summarized in the guide Night flight bans at German airports.
• Airline infrastructure: Airlines prefer airports where they have handling, maintenance or their own staff, because it simplifies the passengers’ onward travel.

Diversions become especially noticeable when a hub is affected. If thunderstorms or a runway closure hit Frankfurt Airport or Munich Airport, flights often spread out to other large airports in the area. Which ones in an individual case, you only see live – and that is exactly the appeal.

The spotter opportunity: why alternate landings are so special

For spotters, alternate landings are one of the few occasions when chance shuffles the flight schedules. A few reasons why the trip can be worth it:

• Rare types at your home airport: A widebody jet at an airport that otherwise sees only medium-haul is a real highlight in your collection.
• Foreign airlines: Airlines that never serve your airport on schedule suddenly turn up on the apron.
• Unusual pictures: A long-haul jet next to regional aircraft, a row of guests on a parking stand that is otherwise empty – such subjects don’t exist in normal operations.
• The onward flight: Anyone who misses the landing often gets a second chance at departure, when the aircraft sets off for the original destination after refueling.

How rare a sighting really is can be put in context with the guide How rare is my sighting?. An alternate landing of a type that otherwise never visits your airport almost always belongs in the top category.

How long does the guest stay?

The window for photos depends heavily on the reason for the diversion:

Reason	Typical sequence	Window for spotters
Weather at the destination	refuel, wait for weather to improve, continue	often short, continuation sometimes after just a few hours
Night flight rules at the destination	overnight at the alternate, continuation in the morning	long, departure usually the next morning
Medical emergency	handover to emergency services, refuel, continue	medium, depending on handling and crew
Technical problem	inspection by maintenance, possibly spare parts or a replacement aircraft	unclear, sometimes several days

The figures are tendencies. Crew duty times can quickly turn a short stop into an overnight stay, and some airlines send a replacement aircraft while the diverted one stays put.

Step by step: from tip-off to photo

For step 4, the guide Tracking an aircraft by registration helps. You set up notifications that take the work off your hands with the article Setting up flight tracking alerts. And if you want to receive your own data on the go, you will find the right setup in the article Mobile ADS-B reception at the spot.

Aviation radio as an additional source

Some spotters want to follow aviation radio during diversions too, to catch decisions earlier. The legal situation is not the same in every country, though: in Germany, listening in on aviation radio without authorization is not covered under the eavesdropping ban of the TDDDG (Germany’s telecommunications and digital services data protection act), and passing on what you heard is expressly forbidden. Details are in the article Is listening to aviation radio allowed?. And please: what you hear on the radio about a medical or technical emergency does not belong on social media.

Staying fair: diversions are exceptional situations too

As appealing as an alternate landing is for you – for passengers, crew and airport staff it means stress. In medical emergencies, a person’s health is at stake, and with technical problems the fire service and emergency services are on duty. A few clear rules follow from this.

How to behave properly during an emergency landing or incident is described in the guide Witnessing an emergency landing: how to behave. Which legal limits apply to photos of affected people is explained in the article Photos of aircraft accidents and emergency landings. In general, even with the greatest rarity: stay in public areas – what is allowed is in the article Is plane spotting allowed?.

What to watch out for

• Not every holding pattern ends in a diversion. Many flights land quite normally after a few laps. Only a course change and descent make it certain.
• Don’t blindly accept displayed destinations. The destination on the live map often comes from the flight plan and is only updated later.
• Observation decks have opening hours. Especially in the evening, when night flight rules trigger diversions, many decks are already closed. Check beforehand which public spots you have left.
• Don’t speculate about causes. You learn the official reason – if at all – from the airline, airport or authorities.
• Fast, but safe. No photo is worth rushing in traffic or ignoring parking bans in front of rescue access roads.

Conclusion

Diversions are exceptions in flight operations, but they follow patterns. Holding patterns, bad weather at the destination, course changes and status messages often reveal them early. If you know the suitable alternate airports in your region and keep an eye on the weather situation at the hub, you will be at the fence at the right moment – and see aircraft that otherwise never come by. With emergencies, the rule always applies: consideration first, camera second.