How to spot test flights, factory flights and first flights on the radar

On the live map, an A321neo has been circling over the North Sea for two hours, departure airport Finkenwerder, destination Finkenwerder, registration D-AV-something. Not a leisure flight gone astray, but a factory flight: a brand-new aircraft completing its production test before it goes to the airline. If you can spot test flights, factory flights and first flights on the radar, you find aircraft that exist in this form for only a few days – in customer colors without an airline registration, in green primer or as the prototype of a new type. This guide shows you the telltale signs, the most important factory airfields and how to plan your day at the fence.

Spotting a test flight: the short answer

You recognize a test flight by four features that usually occur together: a manufacturer callsign such as AIB (Airbus) or BOE (Boeing), a test registration instead of the later airline registration, the same departure and arrival airport and a flight track that looks more like a practice area than a route. Each feature alone can be misleading. If you see three or four of them at once, it is pretty clear.

What kinds of factory flights there are

“Test flight” is a catch-all term. As a spotter it pays to tell the variants apart, because they behave differently on the radar.

Type of flight	What it is about	Typical picture on the radar
First flight of a new-build aircraft	first flight of a freshly assembled production aircraft	round trip from the plant, manufacturer callsign, test registration
Production test	systems, engines and avionics are checked in flight	loops, climb and descent phases, return to the plant
Acceptance flight	customer pilots fly together with manufacturer pilots	similar to the production test, often with an extra letter in the callsign
Transfer within the manufacturer’s network	flight between two sites, for example for painting or outfitting	normal route flight with a manufacturer callsign
Delivery flight	handover flight to the airline	airline callsign, often already the final registration
First flight of a new type	start of a certification campaign	announced, prototype with test equipment, many onlookers

Delivery and ferry flights have an article of their own: Tracking delivery and ferry flights. This one is mainly about the flights before an aircraft belongs to the airline.

Clue 1: the callsign

Scheduled flights transmit a callsign made up of an airline code and a flight number. Factory flights use the manufacturer’s code. For Airbus, the data usually shows the prefix AIB followed by digits. On acceptance flights a letter is sometimes appended – in spotter reports you read, for example, of “AIB560C” for a customer flight of an A321neo. For Boeing the prefix is BOE. The first flight of the Boeing 737 MAX 10 on June 18, 2021, for example, ran as BOE101.

The numbers are not flight numbers in the usual sense and appear in no public flight plan. How callsign and flight number are related in general is explained in the article Callsign vs. flight number: what’s the difference.

Clue 2: the test registration

Airbus first flies brand-new aircraft with test registrations. In Toulouse these are registrations from the French F-WW.. series, in Hamburg-Finkenwerder German series such as D-AV.. or D-AZ… The catch: these registrations are traveling trophies. The same registration is attached to many different new aircraft in turn. At Boeing, by contrast, new aircraft are often already flying with the customer’s registration or a US registration.

For your collection this means: a photo with “D-AVZK” alone doesn’t tell you which aircraft you saw. Only the serial number (MSN) makes the sighting unambiguous. How factory registrations are built exactly is covered in the article Manufacturers’ test registrations, and the basics in the guide Understanding aircraft registrations.

One side effect concerns the technology: an aircraft’s Mode S address (the hex code) is tied to the country of registration. A new aircraft with a French test registration therefore transmits a different hex code than after handover to an airline from another country. Anyone searching specifically by hex code, as described in the article Tracking an aircraft by registration or hex code, has to keep this in mind. More on the technology behind it is explained in Mode S transponders explained.

Clue 3: departure equals destination

A flight from Toulouse to Toulouse or from Finkenwerder to Finkenwerder is hardly anything other than a factory or test flight. Many flight radar services show no destination at all for such flights or enter the departure airport again. Also watch for intermediate landings and go-arounds at other airfields: even first flights don’t always end at the plant. The 737 MAX 10 took off in Renton in June 2021 and, after its first flight, landed at Grant County International Airport in Moses Lake in the US state of Washington.

Clue 4: the flight track

Test flights give themselves away by their geometry. Typical are:

• loops and figure eights over sparsely traveled areas or over the sea,
• long climbs to high altitude followed by descent phases,
• turns and circles at one point, sometimes at several altitudes in succession,
• low passes and go-arounds at the home airport to finish.

How to read symbols, altitude readouts and colors on the map is explained in the article Symbols and colors on flight radar maps. Don’t confuse test loops with ordinary holding patterns: holds have a clear racetrack shape near an approach fix, while test flights are usually more irregular. The difference is shown in the guide Spotting holding patterns on flight radar.

The most important factory airfields

Hamburg-Finkenwerder

The Airbus factory airfield on the Elbe (ICAO EDHI, IATA XFW) has no scheduled traffic. New aircraft of the A320 family dominate here, above all the A320neo and A321neo, plus Beluga transporters. The first flight of the A321XLR also started here: on June 15, 2022, the first aircraft (MSN 11000) took off and stayed in the air for about four and a half hours. Locations, light and directions are in the guide Spotting at Airbus Finkenwerder. The commercial airport is very close by – if you combine both, the Affenfelsen in Hamburg is the classic spot for scheduled traffic.

Toulouse-Blagnac

At Airbus headquarters, factory traffic and scheduled flights share the runways of Toulouse-Blagnac Airport. The A350, A330 and aircraft of the A320 family are built here, among others, and many first flights of new types start here. The first A350-1000 (MSN 59), for example, took off in Toulouse on November 24, 2016 and landed back at its starting point after a good four hours over southwestern France. On the radar the F-WW registrations stand out immediately. The best locations are described in the guide Plane spotting at Toulouse-Blagnac, and next to the Aeroscopia museum you have aviation history and factory traffic in one place.

Seattle: Renton, Boeing Field and Paine Field

Around Seattle, Boeing production is spread over several sites:

• Renton is home to 737 final assembly. The runway is short; the new aircraft take off for their first flight and do not land there again afterward.
• Boeing Field (King County International Airport, BFI) is the destination of these flights. The 737 delivery center is here, where the aircraft are prepared, accepted by the customer and handed over. The Museum of Flight is also on the field.
• Paine Field in Everett is home to the large Boeing plant for widebody jets. From here the first Boeing 777-9 took off on January 25, 2020 for its first flight and landed at Boeing Field after just under four hours. The Future of Flight visitor center is located on the field.

A typical pattern for new 737s: departure from Renton, a test program over Washington State, sometimes with approaches to other airfields, landing at Boeing Field. If you spot in Seattle, you therefore constantly see new aircraft at Boeing Field, often still in greenish protective paint or already in customer colors.

First flights of new types: a special case

The first flight of a completely new type or a new variant is a highlight for spotters – and the opposite of an ordinary factory flight. It is usually announced beforehand, media and fans wait at the fence, and many people follow the track on flight radar services at the same time. There are three things you should know:

• Dates are provisional. Manufacturers only go once weather, technology and test plan line up. Delays of hours or days are normal.
• The prototype looks different. First-flight aircraft often carry test equipment, sometimes striking special liveries and extra antennas. They stay in the test campaign for months and show up again and again.
• The track is predictably unpredictable. The first flight usually stays near the plant or a test area, with lots of maneuvers at medium altitudes.

If you collect prototypes, you will find more ideas in the article Spotting rare aircraft.

Finding factory flights on purpose: step by step

When the test flight stays invisible

Sometimes a factory flight is missing from the map even though you can hear it. There can be several reasons: individual flight radar services hide certain flights, positions are calculated only via multilateration, or an aircraft transmits unusual data during a test. Unfiltered community networks such as ADS-B Exchange often show more in such cases. How MLAT positions come about is explained in MLAT and multilateration, and with a receiver of your own from the guide Build your own ADS-B receiver you get your own raw data around the plant.

What to keep in mind

• Factory grounds are off limits. Photograph only from publicly accessible areas. Plant security at manufacturer sites is often stricter than at commercial airports. The general legal situation is summarized in Is plane spotting allowed?.
• Don’t spread live data from the plant that isn’t public. What a flight radar service shows publicly is one thing – tips from employees or from the factory grounds don’t belong in group chats.
• Don’t treat the registration as an identity. With test registrations the MSN is decisive. Check your match before you share a sighting.
• Plan for patience. Factory flights follow production progress, not your schedule.

Conclusion

Test flights are the rough diamonds of flight tracking. They appear in no flight plan but give themselves away through manufacturer callsigns such as AIB and BOE, through wandering test registrations, through round trips with the same departure and arrival point and through flight tracks full of loops. Finkenwerder, Toulouse and the Boeing airfields around Seattle are the most important stages for them. With filters, alerts and an eye on the serial number, you turn chance finds into planned sightings.