747-100SP

The 747SP is the 747 that went the wrong way on purpose. Every other variant grew; this one had nearly 48 feet cut out of it. Special Performance meant range and speed rather than capacity, and for a decade it was the longest-legged airliner in the world.

Only 45 were built against an expectation of around 200 — but the aircraft is remembered out of all proportion to its sales.

Why it exists

The SP came from a joint request by Pan American World Airways and Iran Air. Pan Am wanted to fly New York to the Middle East nonstop; Iran Air wanted Tehran to New York, which on launch was the longest nonstop commercial flight in the world.

Nothing then flying could do it. A standard 747 had the range only if it carried very little; a smaller aircraft did not have the legs at all. Boeing’s answer was to keep the 747’s wing, engines and fuel, and remove the weight of the passengers instead.

What was changed

• Fuselage sections removed both fore and aft of the wing; the centre section was redesigned. Length fell from 231 ft 10 in to 184 ft 9 in (56.31 m).
• The complex triple-slotted Fowler flaps of the -100 were replaced with single-slotted flaps — simpler and lighter, and acceptable because the aircraft was so much lighter overall.
• The under-wing “canoes” housing the flap mechanisms on full-size 747s were deleted entirely.
• Larger vertical and horizontal stabilisers, and a double-hinged rudder, to keep control authority with a much shorter moment arm.
• The rear upper fuselage tapers into the empennage rather than running straight back.

That last point is why an SP looks subtly wrong to anyone used to 747s: the tail is oversized, the body is stubby, and the wing looks enormous — because relative to the fuselage, it is.

What it achieved

First flight	4 July 1975
Entered service	25 April 1976, Pan Am, New York–Tokyo
Length	184 ft 9 in (56.31 m)
Range	5,830 nmi (10,800 km) with 276 passengers in three classes
Built	45

In May 1976 a Pan Am 747SP named Liberty Bell Express flew round the world in 46 hours 26 minutes, covering 23,137 miles — a record that made the aircraft famous well beyond the industry.

Why it did not sell

The SP was extremely good at one thing and expensive at everything else. It carried far fewer passengers than a full 747 while costing nearly as much to buy and burning four engines’ worth of fuel. It only made money on routes where nothing else could fly at all — and there were not many of those.

Then the routes stopped being special. Twin-engined aircraft with ETOPS approval, and later the 747-400 itself, could fly the same sectors with better economics, and the SP’s reason to exist evaporated.

Production had effectively finished with the 44th aircraft on 30 August 1982. Boeing reopened the line once, five years later in 1987, to build a single final SP for the United Arab Emirates government.

Where they went

A handful survived far longer than the airlines that ordered them, largely as government and VIP transports — the aircraft’s combination of range and modest size suited heads of state well.

The most remarkable afterlife belonged to a former Pan Am and United SP, which NASA and the German Aerospace Center converted into SOFIA, an airborne observatory carrying a 2.5-metre infrared telescope behind a door that opened in flight at altitude. It flew in that role until 2022.

Aside from the 747-8, the SP is the only 747 whose fuselage length was ever changed from the original.