Delivered to KLM throughout the 1970s, 10 747-200 ‘Combis’ were systematically converted to SUDs by Boeing in the mid-80s. We look at how the change was made, and why.
The Stretched Upper Deck (SUD) configuration was a Boeing penchant in the second half of the Me-First decade. The significantly expensive alteration was made to a number of B747-100s and -200s, primarily those owned by JAL and KLM respectively.
But KLM was the airline that took the optional extra and ran with it. 10 747-200s in total were converted for the airline at Boeing’s Seattle FAL.
— Andreas Spaeth (@SpaethFlies) October 13, 2019
The SUD was a straightforward concept: stretch the upper deck to increase capacity. Of the two types, the -200, which entered service in 1971, had more powerful engines and a higher take-off weight. It was thus the first target of the stretch.
KLM no longer flies the -200 in any guise. In the late 1990s the carrier converted most of its variants to carry freight. By 2003 all of its remaining -200SUD variants had been retired or sold to other airlines.
In 2017 one of the last airworthy -200s touched down at Seattle-Tacoma International Airport. Cargo carrier Kalitta Air retired its freighter in April of that year.
What were the benefits of the stretch?
The B747-200 Combi carried cargo as well as passengers. It was fitted with an aft main deck cargo hold separated from the main cabin by a removable partition.
KLM’s 10 aircraft of the type were duly converted to SUDs, adding 280 inches of structure to the upper deck cabin. The hump of the SUD now extended to the rear of the wing rather than finishing at the leading edge.
Writes Airline Reporter, Boeing claimed the new design allowed, “A 10 percent increase in capacity with only a 2 percent change in operating empty weight.
“This means added profit potential, lower seat-mile costs and 5 percent lower fuel consumption per available seat-mile.”
Which other airlines took the option?
In 1982 UTA – since absorbed into Air France – took delivery of one of two converted SUDs (registration F-BTDG/H).
Four years later Boeing stretched two -100BSRs, which mirrored the capacity of the -300, for JAL. JA8170 was fitted with 563 seats and flew until its retirement in 2006. The second SUD was damaged during floods at Don Mueang International Airport in 2011 and scrapped, according to Airliners.net.
In 1997 KLM ordered a handful of its variants to be converted from passenger-cargo combi airliners to dedicated freighters.
The first of the stretched variants arrived at Boeing’s Wichita modifications plant at the end of 1997 and was returned to KLM cargo early in 1998. The interior of the fuselage was configured to enable the SUD to carry as much as a dedicated cargo 747-200: 243,000 pounds of cargo, according to Boeing’s own calculations.
Despite offering some commercial benefits to KLM, et al., the B747-200SUD was not deemed an overriding success. In the end, some were modified to freighters but most were scrapped, and the retro-stretch seems not to have been repeated since.
The configuration, as well-meaning as it was, had a short expiry date. Yet the decision to stretch the top deck undoubtedly influenced the design of the extended hump of future 747 models.