What happens to Flight Testing Aircraft after Testing is over?

Question

Are aircraft used for flight testing typically sold to Airline customers after their use for flight testing is over?

e.g. The aircraft shown in this SE Aviation Question:

Why are these windows on some airplanes red?

Sounds like a lot of money to waste so I expect they would be sold for some revenue but to what end use is the question.

Answer 1

It depends. In most of the cases, the aircraft have been instrumented and pushed so much that it not possible to modify them for commercial flight. In these cases, they are either preserved or continued to be used as test aircraft. In other cases, the aircraft are modified and delivered.

• Boeing 747- The first ever Boeing 747 was used exclusively as a test aircraft and was later handed over to museum. On the other hand all the 747-8s were converted back after test flights and delivered to customers.

• Boeing 777- The first 777s were considered production models, not prototypes and were delivered to customers after testing.

• Boeing 787- It is kind of a mixed bag here- The first three 787s are in museums across the world (two in the US, one in Japan). Boeing is still using one as a testbed, while one more is in storage. Another aircraft used for testing was later modified and sold to the Mexican Air Force.

• Airbus A350XWB- Right now, Airbus is holding all the five testing aircraft and using them for testing or demonstration flights.

• Airbus A380- Airbus has all the test aircraft.

You can check out the production lists of various aircraft here

Answer 2

Prototype aircraft are generally of less value than the production counterparts, since they are heavier and may not have the normal design configuration.

• Boeing 737: The original -100 ended up going to NASA as a research aircraft as NASA 515.
• Boeing 747: At the Museum of Flight.
• Boeing 757: Nicknamed "Catfish", it is an experimental avionics testbed registered N757A.
• Airbus A320: One retained and continued to be used for the type's winglet/engine testing.

Particularly new aircraft (and derivatives thereof) tend to go to customers as testing becomes more refined and the cause of less design changes:

• Boeing 737-800 prototype went to commercial service, now operating as TC-SNY.
• Boeing 737-900 prototype went to Alaska Airlines as N302AS
• Boeing 777-200 prototype went to Cathay Pacific as B-HNL.
• Boeing 777-200LR prototype went to Pakistan International Airlines as AP-BGY

However, not every aircraft can be sold if the aircraft is too unattractive and end up in a museum so many have been scrapped.

Answer 3

Like many of these answers mentioned, it depends. For instance, the 787 program did write off the airframes for the first 6 aircraft due to the extensive number of modifications that were required to those airframes. They do go to museums of strategic importance to either the manufacturer or the kick-off customer and their country. Some of these aircraft end up going into lifecycle fatigue testing or are maintained in the ownership of the manufacturer for follow-on testing that would be for upgrades or newer subsequent models. If the program is a brand new model or significant technological change to an existing model, it has to go through stability and control testing and flutter testing. That literally beats the airframe to hell. It will most likely experience an over-G loading in these tests, and therefore, cannot and should not be used to carry passengers. There would be a potential for cargo in these cases, but then there would be added maintenance costs and operating costs from being structurally modded and heavy. There aren't many that would want to purchase a 'new' aircraft that had gone through the beatings these aircraft take.

Answer 4

In order to reduce the certification time needed, manufacturers usually manufacture more than one testing aircraft, this way several flight tests can be done in parallel.

Once the airplane is finished, keeping those airplanes is a cost and there is no business case to keep all them. However, an airplane model is a living design and during its lifetime (could be more than 50 years, as B737 for example) the airplane design will be updated.

Things as simple as obsolescence of equipments, small improvements, new technologies... not just re-engining the airplane. Those modifications must be certified as well, and some of the means of compliance require a flight test.

So, in this context:

• Manufacturer usually keeps always one of each airplane model, and likely more than one during a period of time.
• Those having less damages and usable for commercial flights (like long haul testing) are usually sold with a discount (and actually very early...)
• Finally, those that are too expensive to keep and not usable for commercial flight are scrapped or sold/donated to institutions.

Anyhow, is a significant amount of money what is lost, but is part of the development cost. Finally is a business case... you can extend the certification period by 1 year and save 2 testing airplanes? Having 1 year more the manufacturing line stopped waiting for the certification? Finally using several testing airplane is a possitive business case.