“I n case anyone is wondering why Brian is referring to the aircraft as a 747-451 instead of a 747-400: the aircraft is a 747-400, the “51” refers to the customer it was originally built and delivered to, in this case, Northwest Airlines. Delta inherited the aircraft when merging with NWA in 2009.”
…but according to this article — which for some reason no longer exists at Puget Sound – Boeing Test Flights — and the “tweet” from Chris Edwards shown above, the Boeing Corporation has abandoned the use of the two-digit customer airline code from its 737, 747, 767 and 777 model lines as of September of 2016, which brings the numbering convention designations in alignment with the 737 MAX and 787 model lines, for which the new designations were initially adopted.
The 737 MAX model line will be referred as 737-7, 737-8 and 737-9.
These changes — which have already been implemented on the certificates issued by the Federal Aviation Administration of the United States — became effective with the following model line numbers for each respective Production Line.
B737 As of line number 6082 — with one exception as of line number 6020 — forward, this model line is now known as either:
B747 As of line number 1534 forward, this model line is now known as either:
747-8I for the Intercontinental series; or
747-8F for the Freighter series
B767 As of line number 1102 forward, this model line is now known as:
767-300F, as only the Freighter series is currently in production
B777 As of line number 1422 forward, this model line is now known as either:
777-F for the Freighter series
This Boeing 777-328ER aircraft operated by Air France is now referred as a Boeing 777-300/ER.
This Boeing 737-790 aircraft operated by Alaska Airlines is now referred as a Boeing 737-900WL.
This Boeing 737-3H4 aircraft operated by Southwest Airlines would now be referred as a Boeing 737-800WL — if it were still currently in service.
I first started writing about this months ago and due to a number of factors — including travel, of course — I never got around to finishing this article; so please accept my apologies if this is old news to you.