Monday, January 13, 2014

The Life and Times of the Boeing 747SP

The Boeing 747 is perhaps the most iconic and famous commercial aircraft to ever take to the skies; recognized the world over by its unique shape and distinctive upper deck hump.  To date Boeing has delivered 1,474 jumbo jets across 16 different models since production began at the Everett factory in 1967. According to Boeing the 747 fleet over the course of its 40+ years in service has traveled 48.3 billion miles and transported 5.6 billion people around the globe.  By all accounts the aircraft has been a runaway financial and commercial success.

The 747-400 during its 20 year production run from 1988-2008 was responsible for 694 orders, making it far and away the most successful of the 19 commercial 747 models offered by Boeing.  To date the 400 series has accounted for roughly 47% of total program deliveries.  But lost amid the 747's long list of accolades, unparalleled sales success and decades of faithful service with the world's airlines is the interesting and obscure story behind the development of the 747SP.

The 747SP is a brief, and largely forgotten page in the 747's proud history.  Not many books or articles have been written about this fascinating aircraft, largely because it never realized the commercial success of its larger siblings.  This stubby 747 model was by many measures a commercial failure, with Boeing only managing to sell 45 during the aircraft's eight year production run from 1976 to 1982, 1987.  The line did reopen again briefly in 1987 so that Boeing could produce one final aircraft.

Yet despite its lackluster sales the aircraft filled a very important niche market for Boeing at the time and pioneered the concept of ultra long range flights, paving the way for the 400 series that followed.  The SP's exceptional performance and long range opened up new routes, making nonstop flights between city pairs like Sydney-Los Angeles, Johannesburg-London and New York-Tokyo a practical reality for the first time. The 747SP over the course of its airline career set many performance benchmarks for its class including the fastest round the world flight from pole to pole.  Unfortunately the airplane never truly found widespread acceptance in the market outside of its ultra long range niche.  So just how did this curious aircraft come to be and what were the market factors that led Boeing to design this unusual aircraft in the first place?

The year was 1971 and McDonnell-Douglas had just successfully delivered the first DC-10 to launch customer American Airlines.  The DC-10 had been conceived largely in response to a specification issued by American Airlines for a wide body jet that was smaller in capacity than the 747 but had equivalent range and could operate from shorter runways where it was not feasible to operate a 747.  The tri-jet design that emerged was enthusiastically embraced by American which launched the aircraft in 1968 with an order for 25 airplanes, United followed closely behind ordering 30 DC-10s.

At the same time Lockheed which had been largely absent from the commercial airline market since launching the Lockheed L-188 Electra turboprop which suffered through a spate of headline grabbing crashes shortly after entering service in the late 1950's.  The negative press and passenger avoidance of the aircraft had greatly affected sales of the troubled airliner and had caused the manufacturer to shy away from the commercial market.  With the American requirement Lockheed was eager to jump back into the game and begin development of its own tri-jet the L-1011.  After failing to win over American, Lockheed launched the aircraft with firm orders from TWA and Eastern.

Technical/Performance Comparison of the L-1011-1 and DC-10-10 © Gregory Maxwell, 2014

McDonnell-Douglas and Lockheed were on a similar trajectory with the DC-10-10 and L-1011-1 both scheduled to enter commercial service in 1971. Unfortunately for Lockheed Rolls-Royce's revolutionary new RB211 engine which made use of composite materials to save weight and reduce operating costs ran into serious development issues.  The issues became so severe that they eventually forced Rolls-Royce to shut down and seek government protection.  Unlike McDonnell-Douglas which offered DC-10 customers the choice of General Electric or Pratt & Whitney engines Lockheed had opted for an exclusive agreement with the British engine manufacturer. Rolls-Royce was eventually bailed out by the British Government after assurances were received from the United States government, over the objections from then California governor Ronald Reagan, that the U.S. would guarantee the loans Lockheed needed to finish the L-1011 project.  After more than a year delay the first L-1011-1 was delivered to launch customer Eastern Airlines in April of 1972.

Meanwhile in Seattle Boeing had been closely following the development of the DC-10 and L-1011 and soon realized that the new tri-jets exposed a large hole in the company's product line between the aging 169 seat 707-300 and the much larger 380 seat 747-200B.  Boeing had no effective product in the long range, mid capacity segment of the market. The DC-10 and L-1011 had carved out a niche that was costing Boeing potential customers.  Not only were new customer flocking to order the new tri-jets but existing 747 operators were placing orders as well.  The initial models of both the L-1011 and DC-10 didn't have intercontinental reach but both manufactures were hard at work developing long range derivatives which would hit the market in a few short years.

Since the late 1960's Boeing had been studying various concepts involving shortened and modified two and three engine 747 designs to match the capacity requirements of the DC-10 and L-1011 proposals.  The major problem with any four engine 747 derivative was overcoming the 33% fuel burn deficit a four engine airplane would have when compared to a three engine jet.  Very simply the more engines an aircraft has the heavier the airplane is, the more fuel it burns and correspondingly the more costly it is for an airline to fly and maintain.

Airplanes are delicately balanced machines and the wing design of an aircraft is largely predicated on the placement and weight of the engines.  While wing mounted engines add weight and increase drag, they also help to dampen wing movement and limit the wing's twisting tendency.  The problem for Boeing engineers was the wing on the 747 like the 707 before it had been designed and balanced for the weight of four engines.  In the 747's case the four engines and their associated components represented 57,000 lbs of weight.  By removing an engine from each of the 747's wings and thus reducing the weight on each wing by 14,250 lbs. the natural dampening effect provided by the weight of the 2nd engine was lost which upset the precise balance of wing bend and twist built into the design; this negatively effected its performance and flight profile.  Boeing realized that any twin or tri-jet design concept that incorporated two wing mounted engines would require significant redesign of the wing structure.

Boeing Tri-Jet Concept Model (Boeing Archives)

On paper a 747 twin-jet concept seemed to have real promise.  It would cut fuel burn and operating costs dramatically over the existing 747 as well as the competing Lockheed and McDonnell-Douglas tri-jets but there were significant regulatory and engineering problems that proved difficult to overcome.  First a twin jet 747 would need bigger more powerful engines.  The problem, they didn't exist and it would take years for General Electric, Pratt & Whitney and Rolls-Royce to develop a new class of engine suitable for a 747 twin-jet.  Some engineers were doubtful that the technology even existed to develop such an engine in the near term.

Secondly and more problematic was the regulatory problem of convincing the FAA and other global aviation agencies to certify a twin-engine aircraft for trans-oceanic flight.  Up to this point largely due to the distant memories of unreliable piston aircraft the FAA limited twin engine commercial aircraft to flying a maximum of 60 minutes from the nearest suitable diversionary airport, while ICAO recognized a 90 minute limit.  The FAA believed at the time that four engine aircraft were most suitable for trans-oceanic flights.  McDonnell-Douglas and Lockheed had convinced the FAA that three engine aircraft could perform this mission just as safely as a four engine jet, but two engines was a leap of faith that the FAA was not ready to embrace in 1971. Without certification for trans-oceanic flight from the FAA any twin-jet would be severely limited in the types of routes that it could be deployed on thus making it very unattractive to airlines.  A reality that would severely blunt early sales of up-start Airbus Industries revolutionary A300 widebody twin jet.

The tri-jet tail mounted engine concepts were also problematic as they added considerable weight in the tail which effected the aircraft's center of gravity and changed the delicate balance of the airplane, not to mention the massive structural modifications required to the tail to accommodate a third engine.  While a tri-jet concept was more desirable from an operating cost standpoint the company was also cognizant of passenger surveys which indicated an overwhelming preference for a four engine airplane for trans-oceanic flights.

No one in Everett was interested in building an all new aircraft.  That would simply take too much time and cost too much money to develop and would place Boeing well behind Lockheed and McDonnell-Douglas in the market. Boeing didn't have six or seven years to launch a competitive answer they need something that could be built cheaply and be brought to market quickly.  Eventually led by Joe Sutter, the father of the 747, it was agreed that the best course of action was to shorten the existing 747 fuselage and retain the aircraft's existing wing and four engine arrangement.  Sutter reasoned that while the shortened 747 might not be able to match the DC-10 or L-1011's fuel burn or operating costs it would retain commonality with existing 747's which would reduce manufacturing and production costs for the company.  The parts and systems commonality with existing 747's would also save current 747 operators considerable money in training and maintenance expenses and this just might be enough to sway them from purchasing the DC-10 or L-1011.

Technical/Performance Comparison of the 747SP and 747-200B © Gregory Maxwell, 2014 

With a concept in place Boeing set about optimizing and tweaking the design of the 747SB or "Short Body" as it was then called.  The existing 747 fuselage was shortened by 48 feet to accommodate around 280 passengers in a two class arrangement which closely matched the competing DC-10 and L-1011's capacity and placed it 100 seats under the existing 747-200B. The new aircraft retained the standard 747 wing, in combination with a 2 ft. taller tail and 10 ft. longer horizontal stabilizer span.  The shortened aircraft, with its reduced structure and components enabled Boeing to lighten the airplanes gross weight by 125,000 lbs when compared to the standard 747 air frame.  A lighter airplane led to a 20% reduction in fuel burn, which in combination with the 747's speed and the projected 4,000-6,000 foot higher cruise altitude gave it the exceptional capability to fly 270 passengers and cargo almost 7,000 miles!  A distance well beyond the reach of the DC-10 or L-1011.  The aircraft's performance if it penciled out would give it the lowest seat mile costs of any aircraft of its size class, besting both its tri-jet competitors.

Despite the aircraft's promise on paper the Boeing board was not entirely convinced of it's commercial potential, giving the project only incremental approval in June, 1973.  Around that same time Pan Am issued a firm requirement for an aircraft to deploy on long range routes with demand too thin to support a full size 747.  Both Lockheed and McDonnell-Douglas pitched long range derivatives of the DC-10 and L-1011.

To highlight the new 747's performance advantage over the competition Boeing re-designated the aircraft as the 747SP for Special Performance.  Two months later in August of 1973 the Boeing board formally approved the aircraft launch, believing that a launch order from Pan Am was inevitable.  The company took a substantial risk by green lighting the SP before receiving a minimum order commitment, but by this time most inside the company had been won over by the SP's impressive economics.  Furthermore Joe Sutter had thrown his full support behind the project and that was enough to convince most skeptics that the aircraft would be embraced by airline customers around the world.

Boeing's marketing department had identified a potential market for 214 SP airplanes with all but 31 frames being for new aircraft.  The remaining orders would likely come from order conversions from the larger 200B model.  This data helped convince Boeing brass that the derivative aircraft would not cannibalize the existing 747 market, but instead enhance the appeal of the existing 747 to both new and current customers. Top sales targets were Pan Am with a requirement for 20 aircraft followed by El Al, Japan Airlines and Qantas which combined Boeing believed would generate demand for another 28 aircraft.  With these potential order the 747SP would quickly surpass the predicted break even point of 45 aircraft.

While the primary market for the aircraft was long range trans-oceanic routes, the company also felt the aircraft had the potential to replace aging 707s and DC-8s on short to medium range routes.  Boeing also envisioned a small market for the aircraft as a VIP transport for heads of state from countries around the world and as a potential replacement for the current VC-137s.  Engineers also studied a combi version which could accommodate 194 passengers and 1,512 cubic feet of cargo on the main deck in a similar arrangement to the popular 747-200M.

Pan Am signed on as the launch customer at the end of September, ordering 10 aircraft and securing options on an additional 15 aircraft.  The order including spares was valued at $280 million, with a per unit cost of approximately $27 million per aircraft, which was $3 million less than the standard 200B model at the time. Boeing established a very aggressive two year development, production, and testing schedule with delivery of the first 747SP to launch customer Pan Am contracted for the first quarter of 1976.  The compressed schedule was necessary to try to make up lost ground to Lockheed and McDonnell-Douglas.  The long range DC-10-30 derivative had already been in service with launch customer Swissair for almost a year and the L-1011-500 was scheduled to enter service by 1977.

Technical/Performance Comparison of the L-1011-500, DC-10-30 and 747SP © Gregory Maxwell, 2014

Well before the project received approval from the board, engineers were hard at work in the wind tunnel refining the SP's design.  Over the course of  19 months from April 1973 to November of 1974 utilizing both high and low speed wind tunnels the team established the aircraft's drag ratio, investigated the airframe's flutter characteristics and validated predictions of aerodynamic loading on the wings and vertical and horizontal stabilizers.  By the close of testing the team determined the low speed drag of the SP was less than anticipated and aerodynamic loads carried by the wing were lower than expected which provided an opportunity for Boeing to shave more weight out of the wing support structure.

The aircraft that emerged form the wind tunnel was much more complex than just a short bodied 747.  The entire fuselage from the wing's trailing edge to the tail of the aircraft was redesigned specifically for the SP. The tail section received particular attention with the entire fuselage section under the vertical stabilizer being re-contoured.  These changes effected the vertical position of the tail fin, making it's base 38 inches lower than the standard 747.  To compensate for the reduced moment arm of the shortened fuselage the vertical stabilizer's height was increased by five feet and a double hinged rudder was added.  Addition of the new rudder required internal stiffing of the tail to withstand the higher aerodynamic loads imposed on it.  In order to counteract changes in the aircraft's pitch characteristics both horizontal stabilizers were lengthened by five feet.  The additional fuselage structure, taller tail and increased span of the horizontal stabilizer combined to make the 747SP fuselage weight 1,500 lbs greater than the standard 747.

While Boeing chose to retain the standard 747 wing on the SP the internal structure was significantly modified to reduce weight.  These changes were possible because the wing loading on the 747SP was about 20 lbs per square foot less than the 747-200B.  To save weight Boeing employed reduced gauge metals in the wing spars, ribs, skin and stringers in the wing box and center fuselage sections.  In an effort to further reduce the weight of the wings engineers designed a single-slotted variable pivot flap system.  The single-slot design was much less complex than the triple-slotted flap system employed on the standard 747 and removed 12,000 lbs in weight from the wing structure.  The final results of the SP's weight savings initiative were impressive as the finished aircraft was 45,000 lbs lighter than a comparable 200B model.

747SP Single-Slotted Flap Design © Gregory Maxwell, 2014

747-200B Triple-Slotted Flap Design © Gregory Maxwell, 2014
The final configuration was frozen in April of 1974 and by that time customer specifications for the Pan Am and Iran Air aircraft had been complete.  To this point no additional customers had formally announced orders for the 747SP although Japan Airlines had signaled an intent to purchase the aircraft.

To ensure the 747SP retained maximum commonality with the rest of the 747 family and thus reduce the hours of training required for a current 747 pilot to transition to the aircraft, Boeing went to great lengths to ensure the SP's flight handling characteristics and aircraft systems closely matched its larger and heavier siblings. To achieve this goal they used an advanced engineering simulator which compared the flight characteristics of the the SP to the standard 747.  A sophisticated computer program analyzed the response of both the SP and the standard 747 in different flight regimes through the entire flight envelope.  Of particular interest was the handling difference of the SP in a low speed, high drag configuration such as approach and landing.  The information collected was then processed and used by the design and engineering team to make adjustments to the control system before the aircraft ever left the ground.

The original 747 static test frame was brought out of storage to serve as the engineering mockup.  The airframe was cut down to the 747SP specifications with sections being removed in front of and behind the wing and a new aft body section was manufactured and installed.  Using the actual airframe allowed engineers to test fit everything from wiring, rigging of flight controls and fitting of insulation and ducting.  The right wing was also attached to test the configuration of the new, lighter single slotted flap system.

Meanwhile in Renton designers were busy working with the interior mockup of the 747.  The original full length 747-100 interior mockup just like the engineering frame was modified to meet the exact specifications of the 747SP.  Cabin mockups even to this day play an important roll as they allow airline customers the opportunity to test fit different interior configurations and see how they work from a practical standpoint and effect crew work flows.  In addition the mockups are used to stage promotional sales photos and develop other marketing materials that are used to sell the aircraft to perspective customers.

In order to maximize the interior space of the 747SP Boeing partnered with customer airlines and the long time Boeing consultant Walter Dorwin Teague Associates.  One product of this collaborative team was the innovative longitudinal (side facing) arrangement of the forward galley.  The design allowed flight attendants from both the first class and forward section of coach to work and serve simultaneously from the same galley space.  The arrangement also provided the crew increased privacy, more working space and caused less interference with passenger boarding.  A self contained lift was built into the galley to allow flight attendants to transfer food and beverage carts easily between the main deck galley and the upper deck service station. A second coach service galley was located just forward of the rear pressure bulkhead at the back of the passenger cabin.  This rear galley retained the standard forward facing arrangement.

Graphic depicting standard cabin layout of the 747SP,  inset photo shows longitudinal galley © Gregory Maxwell, 2014
The main deck passenger cabin was arranged into four service zones, with each zone corresponding to one of the four main fuselage body sections brought together during final aircraft assembly.  Zone A incorporated the first class cabin in fuselage body Section 41 in the nose of the airplane and had space for 18 first class passengers.  Zone B in body Section 42, between the nose and wing join was designed to accommodate 16 additional first class seats or 30 coach seats in a 3-3 layout as well as the galley and four lavatories.  Zone C comprised the main coach cabin in body Section 44 where the wings were joined to the fuselage.  This space contained room for 136 passengers in a traditional 3-4-3 layout with space for three lavatories, with one forward and two aft.  Zone D encapsulated in body Section 46 from behind the wing back to the rear pressure bulkhead, contained the rear coach cabin with seating for 86 passengers again in a 3-4-3 layout and two lavatories were located in the forward section of this cabin.

Assembly of the first 747SP began in earnest at the Everett factory in early November of 1974, when pieces of the aircraft's wings were loaded into the initial position of the 747 line.  A short three months later in February of 1975 the wings were joined to the center wing box.  All the while work continued on the five major body sections that would make up the 747SP fueslage in other parts of the factory.  The sequence of assembly for the 747 required that the center wing box and completed wings be joined to the center fuselage (Section 44) before the nose (Section 41), forward (Section 42) aft fuselage (Section 46) and tail (Section 48) were joined to the center fuselage.  Following the completion of the center fuselage Section 44 the major components including the ailerons, engine pylons, outboard flaps, spoilers and leading edge were installed on the wings.  With all pieces of the fuselage joined and aligned the horizontal stabilizer, tail and landing gear were subsequently installed and the aircraft for the first time began to roll down the line its weight supported by the five landing gear assemblies and 18 tires.

Photo of first 747SP on Everett production line, inset shows major component assemblies (Boeing Archive)

As the aircraft entered the last stages of final assembly the guts of the airplane including flight deck instrumentation, wiring, hydraulic lines and environmental controls along with the APU, inboard flaps, tail cone, landing gear doors and radome were all installed.  One of the last and most delicate steps was the hanging of the rudder on the tail.  Installation of an airplane rudder is a very precise and slow process, as the rudder must be balanced exactly to ensure its proper function and alignment.  Even the added weight of the paint of the customer livery is important to consider when hanging the rudder and for this reason the rudder is painted in an airline's full colors prior to installation.

With assembly complete the first 747SP was rolled out of the factory and into the paint hanger to receive its eye catching red, white and blue scheme specially designed by Boeing for the new 747 model.  Boeing announced the official roll out of the airplane would occur on May 19, 1975 with the first flight anticipated to occur in early July.

As the big day finally arrived thousands of Boeing employees, invited guest, political dignitaries and airline representatives from Pan American, South African Airways and Iran Air all gathered in front of the massive 747 factory doors eagerly awaiting the grand entrance of the newest member of the 747 family.  Vice President and General Manager of the 747 Division Kenneth F. Holtby described the 747SP as "a real winner," and praised the team for delivering the aircraft under budget and ahead of schedule.  He was confident once flight testing began that the aircraft would prove out its performance and easily meet and exceed its performance targets.  Pan Am Senior Vice President of Technical Operations John M. Wolgast added that he believed the 747SP would reign supreme in its class forever.

When the doors finally opened and the first SP entered the daylight carrying Pan Am registration N530PA it was a sight to behold.  Boeing had arranged especially for the roll out ceremony for the first 747-100 test aircraft RA001 to be parked next to the 747SP to provide a since of scale and highlight the size difference of the two aircraft.

Photo of the 747SP's Official Rollout Ceremony on May 19, 1975 (Boeing Archives)

Following the pomp and circumstance of the roll out, engineers went back to work preparing the aircraft for its ambitious test program.  365 hours of flight testing were planned for the three aircraft test program. Because the 747SP was not a new aircraft but rather a derivative the number of test hours required by the FAA in order to receive certification was much lower than the 1,440 required of the original 747.

For the purposes of the test program aircraft number one (N530PA) slated for delivery to launch customer Pan American Airways was re-registered N747SP.  The second test aircraft N247SP was expected to join the test program in August with the third N347SP to follow in October.  A fourth 747SP, N40135 due to be completed in November would serve as a reserve aircraft to help maintain the flight schedule in the event that one of the three primary aircraft experienced a technical fault.  Until the other aircraft came online N747SP would serve as the sole test aircraft and following the ceremonial first flight was scheduled to perform a full battery of tests in its first month, including stability of flight, control response, stall recovery and low speed airplane drag tests.

Over 250 Boeing employees were directly involved in the aircraft's flight test program, including pilots, flight test engineers, instrument specialist, photographers, mechanics and a slew of technicians who recorded and analyze the results of each flight test sorties.  Captain Jack Waddell, Boeing's Chief Test Pilot and 747 project pilot since the program's inception in 1966 was chosen as captain for the 747SP's first flight. Waddell had also been at the controls of the first 747, RA001 on its very first flight in 1969.  The first officer was none other than Lew Wallick, then director of the 747SP Flight Test Program.  Flight Engineer Kenneth R. Storms, Boeing's chief Flight Engineer rounded out the crew.

On July 4, 1975, ten days ahead of schedule the three man crew boarded N747SP and prepared the aircraft for its maiden flight.  By all accounts the flight was routine for a derivative aircraft as the crew worked through the initial handling and control tests, airspeed calibration and fuel burn measurements.  Feeling confident in the aircraft's performance captain Waddell decided to push the aircraft a little, performing a full stall, something that was usually not done on an aircraft's maiden flight.  In addition the crew flew the airplane up to its maximum operating speed of 0.92 mach, reaching 630 mph and over 30,000 feet in altitude.  The aircraft handled so well and experienced so few problems that after a quick check out and data read out it was cleared by engineers for a second test flight later in the day.

N247SP, the second test aircraft made its initial flight on August 14th and was quickly integrated into the test plan.  With FAA test pilots on board to observe the certification process the aircraft demonstrated up to its maximum design speed of 445 knots that it was flutter free.  The stall tests were also completed, with the airframe being subjected to over 80 stalls in various weight and cg positions as required.  The airplane was flown up to 46,000 feet to test the engine performance at high altitude cruise.  To the flight test crew's surprise the aircraft still maintained a 600 foot per minute rate of climb.  46,000 feet was 1,000 feet above the airliner's certified in service maximum cruise altitude of 45,100 feet.

Test Airplane N747SP performing Velocity Minimum Unstick Test at Edwards AFB, CA © Gregory Maxwell, 2014

By October the two 747SP aircraft N747SP and N247SP had accumulated 160 flight hours and the test program was ready to move into the second phase of testing at Edwards AFB.  N747SP was flown to the isolated California base to prove out the aircraft's takeoff and landing performance.  As part of these test the pilots also performed the Velocity Minimum Unstick Test, deliberately over-rotating the airplane onto its tail to determine the minimum flying speed required to achieve takeoff.  During brake testing a lightly loaded 747SP accomplished a full stop landing in only 1,600 feet, without the use of a primary (turbine) reverse thrust system which had been removed during the aircraft's design phase to save an additional 1,100 lbs of weight.

While the three primary aircraft carried out the bulk of the flight test plan aircraft number four, N40135, fresh from its maiden flight on November 3, 1975 embarked on a grand world tour to introduce the 747SP to perspective customers, the media and flying public.  The aircraft outfitted with a finished Pan American interior departed from Boeing Field in the early morning hours of November 11th bound for New York. A day later the airplane with 200 passengers on board departed on the first leg of its trip flying nonstop from New York JFK to Tokyo's Haneda Airport.  13 hours and 33 minutes later N40135 touched down on Japanese soil having flown 7,015 miles without refueling.  The 747SP over the course of the flight reached a cruise altitude of 46,000 feet and a speed of Mach 0.86.  Remarkably upon landing in Tokyo the jet still had 30,000 lbs of fuel in its tanks.

Among the invited guests on the flight was a contingent from Japan Airlines.  JAL had yet to order the 747SP and was currently operating the DC-8-62 on the New York-Tokyo route.  With insufficient range to make the flight nonstop the DC-8-62 required an en-route refueling stop in Anchorage which added several additional hours to the total trip time.  Boeing was quick to point out to JAL the 747SP's 27% fuel burn advantage over the DC-8-62.

Map Generated by Gregory Maxwell using the Great Circle Mapper © Karl L. Swartz

Following the stop in Tokyo the SP flew on across Asia stopping in Taipei, Singapore, Kabul and Bombay before turning east towards Sydney.  After a brief stay in Sydney the jet flew nonstop 7,143 miles to Santiago, Chile.  Further stops on the South American continent included LaPaz, Quito and finally Caracas before heading on to Mexico.  The next leg was the longest of the entire trip with the globe hopping airplane flying 7,205 miles between Mexico City and Belgrade, in the process becoming the first airliner to fly nonstop between Mexico City and the European continent.  A feat which is all that more impressive when you consider the 7,341 foot altitude of Mexico City's airport.  From Belgrade the team flew on to Athens, Lusaka, Nairobi and Abidjan.

The 747SP made the trip home to Seattle with a single stop in Kingston Jamaica.  When it was all said and done N40135 had traveled 72,152 miles and visited 18 cities on six continents and safely transported more than 2,300 passengers on 20 demonstration flights over the course of its 29 days journey.  Not only was the aircraft's remarkable range on display but the aircraft proved to be extremely reliable requiring minor maintenance on the APU only twice during the entire trip, and neither occurrence delayed a scheduled departure.

The 747SP test program officially concluded on December 22nd two weeks ahead of plan, with the three dedicated test aircraft collectively logging 544 hours and 27 minutes of flight time.  A further 140 hours were logged by the number four aircraft N40135 over the course of its world wide demonstration tour.  Despite completing the certification tests, the receipt of the official FAA type certificate was delayed by several months until two deficiencies found during flight test could be corrected.  The first involved a localized shock wave that manifested around the new fuselage fillet, requiring Boeing engineers to redesign the fillet.  A second more serious issue was discovered on a test flight when the lower rudder on N747SP separated from the tail after experiencing greater than expected aerodynamic loads.  Amazingly due to the split rudder design the flight crew didn't even notice the absence of the lower rudder, and were not aware it had departed the aircraft until the chase pilot informed them.  To fix the issue the lower rudder and the attachment points were strengthened to prevent a re-occurrence.

With award of the FAA type certification slipping into early 1976, Boeing was forced to inform launch customer Pan Am that delivery of its first aircraft would be delayed.  Finally after a two month delay the FAA now fully satisfied with the airworthiness of the aircraft officially delivered the 747SP's supplemental type certificate on February 4, 1976, paving the way for delivery to Pan Am and the types introduction into commercial service.  A month later on March 5th Boeing handed over the keys to N533PA "Clipper Freedom" to eager launch customer Pan American Airways.  The airplane formerly, N40135 the globe trotting 747SP was the fourth production airplane built but first to be finished in Pan Am's full customer configuration.

After testing N747SP was returned to Everett to be refitted into Pan Am's configuration, joining N742SP and N743SP which were also being reconfigured prior to customer delivery.  Pan Am received their second SP "Clipper Constitution" N532PA a few weeks later on March 29th and by the end of July Boeing had delivered 12 total aircraft to customers.

Pan Am inaugurated commercial service with the aircraft on April 25, opening the new nonstop Los Angeles-Tokyo route.  A day later the first nonstop New York-Tokyo flight departed for the 13.5 hour flight west.  The 747SP cut more than 3.5 hours off the normal route time, due to the lack of the requisite fuel stop in Anchorage required on the 200B.  Initially the New York-Tokyo flight was offered on a weekly frequency but within 12 months was upgraded to daily frequency due to its overwhelming popularity with passengers. With the first few months of commercial service under its belt, Pan Am was delighted with the stubby 747's performance and its excellent dispatch reliability of 97%.  The Pan Am SP fleet was averaging 10.9 block hours per day and steadily climbing.

Map Generated by Gregory Maxwell using the Great Circle Mapper © Karl L. Swartz

In December Pan Am upped its game again by introducing one stop service between New York and Australia and New Zealand via San Francisco.  Flight PA815 departed San Francisco flying nonstop to Auckland, New Zealand, a distance of 6,516 miles.  The return flight PA816 departed Sydney flying 7,475 miles nonstop to San Francisco and then on to New York.  Flight 816 held the title of the world's longest scheduled nonstop commercial flight for several years.

South African Airway was the second airline to receive delivery of the 747SP and on its delivery flight, ZS-SPA, the airline's first SP, flew from Everett nonstop to Cape Town South Africa covering a unbelievable distance of 10,290 miles in 17 hours and 22 minutes.  When the aircraft landed it still had 38,500 pounds of fuel in its tanks enough for a further 2 hours and 27 minutes of flying.  To make the ultra long flight extra fuel was carried in temporary rubber-nylon bladders secured in the lower deck cargo holds.  At takeoff the aircraft weighed 713,300 lbs a full 50,000 more than it would during normal line service.  The flight easily bested the previous World Record for the longest flight by a commercial aircraft set by a DC-8-53 in 1962 on a flight from Tokyo to Miami which covered 8,792 miles.

Following its record breaking delivery flight South African Airways pressed the 747SP into service on its flagship Johannesburg-London route.  The airplane proved to be ideally suited to the route given Johannesburg Airport's 5,580 foot elevation and warm temperatures. While the airline's 747-200B fleet could make the flight nonstop on cooler days, when the temperature elevated in the summer months a mandatory fuel stop was required.  In addition the 200B's massive capacity routinely outstripped passenger demand on the route.  The 747SP provided the ideal mix of capacity and range that South African needed on its long and circuitous Apartheid restricted routes.  To further demonstrate the airplane's incredible capability South African flew an SP with 224 passengers 8,010 miles nonstop between New York and Johannesburg.

South African Airways Boeing 747SP (ZS-SPC) shown its original 1976 delivery colors © Gregory Maxwell, 2014

Meanwhile the Boeing sales and marketing staff were hard at work trying to sell the airplane to the world's airlines.  The timing of the 747SP's introduction was ideal from the standpoint that many long-range, narrow-body DC-8's and 707's in the world's fleet were aging and their rising operating costs were making them a liability for which the airlines were seeking a replacement.

Boeing offered customers the choice of five gross-weight options for the 747SP.  The basic SP had a 660,000 lb maximum takeoff weight, with a minimum option of 630,00 lbs and a maximum of 700,000 lbs.

Customers had the choice of either the General Electric CF6, Pratt & Whitney's JT9D-7 or Rolls-Royce RB211-524 engines to power their aircraft.  Pratt & Whitney offered a variety of thrust ratings on the JT9D from 46,950 lbs up to 50,000 lbs.  Rolls-Royce's RB211-524 engines were the most powerful engines offered for the 747SP with a maximum thrust rating of 51,600 lbs.  Pratt & Whitney engines were far and away the most popular choice for 747SP operators, being selected for 39 of the 45 total 747SP's built. The remaining six aircraft were powered by Rolls-Royce RB211-524 engines, while General Electric's CF6 gained zero orders over the course of the program.

Despite its shortened size the 747SP had an impressive lower deck cargo capacity with room for 20 LD-1 containers, ten less than the standard 747.  In total the SP's lower hold could accommodate 3,460 cubic feet of cargo with 400 cubic feet of additional space available for bulk cargo.  Both lower deck cargo doors were identical in size to the standard 747 allowing for seamless transfer of cargo between the SP and other 747 variants.  Importantly, this also meant that all existing standard unit loading devices were compatible with the 747SP.

The 747SP was grabbing headlines around the world, and smashing world records everywhere it went. Customers like Pan Am and South African were publicly lauding the aircraft for its performance, efficiency and profitability, but for some reason this wasn't translating into new customer orders.  From Boeing's perspective the SP appeared to have everything an airline could want.  It was cost effective, offered great performance, and had incredibly long range that enabled airlines to fly a sizable number of passengers and cargo nonstop between just about any two points on the globe from almost any jet-capable airport in the world.

For operators who didn't need the capacity of the standard 747 and couldn't afford the price tag the SP offered a foot in the door of the 747 club.  The smaller SP had less seats to fill and had the range to connect major centers in Africa, Asia, Middle East and Oceania to North America and Europe through nonstop service for the first time.

Depictions of the 747SP in Perspective Customer Liveries © Gregory Maxwell, 2014

But for many of these operators the 747SP proved to be too much airplane. Most airlines simply didn't need the SP's globe spanning range for their modest sized route networks where a 707 sized airplane was the ideal fit for the market demand.  There was a very limited niche market where the SP's impressive range and performance were truly needed.  All the while the standard 747-200B's fuel economy and range were steadily improving with refinements to the aircraft and engines allowing the 200B to progressively fly routes of similar length to the SP.  The 200B's incremental improvements made the 747SP less attractive to existing 747 operators who could now exploit the larger 747's capacity to maximum benefit.

The SP's sticker price of $28 million was also prohibitive to many carriers and placed it at the top of its class, $1.5 million above the competing long range McDonnell-Douglas DC-10-30.  Boeing pitched the 747SP to 40 different airlines, among them Air New Zealand, BWIA, British Airways, Cathay Pacific, Delta, El Al, Iberia, JAL, Singapore and Zambia Airways.

The battle for orders between Boeing, McDonnell-Douglas and Lockheed was fierce, with the DC-10-30 proving to be the biggest competitive threat to the 747SP.  In order to counter the sales success of McDonnell-Douglas's tri-jet Boeing armed its sales staff with a handbook that detailed exactly how the SP was superior to the DC-10-30.  Among the points in Boeing's favor the SP had a higher maximum gross takeoff weight, greater fuel capacity, it had a higher seat count across all configurations from a single class all economy layout to a three-class arrangement.  The 747SP could transport its larger payload a much greater distance nonstop than the DC-10-30.  The cabin was wider and provided more room for passengers and their cabin luggage.  The lower deck cargo capacity of the 747SP was comparable to the DC-10's when you took into account the 30 series need for auxiliary fuel tanks in the belly of the aircraft which displaced cargo.  The DC-10 couldn't match the SP's takeoff, landing and climb performance nor its service ceiling. The SP's 6,000 foot higher cruise altitude translated to significantly less turbulence for passengers and an increase in fuel efficiency.  Boeing's short body 747 was also noticeably quieter than the DC-10 on takeoff and approach.  Boeing also claimed the 747SP's seat mile costs were 11% lower than the DC-10 and that the aircraft had a 9-12% higher revenue potential due to its larger seating capacity.

But in both the domestic and international short and medium haul markets the 747SP was overkill and its range and performance advantage over the DC-10 and L-1011 was a moot point.  The fuel efficiency of the tri-jets proved to be a huge advantage and something the 747SP struggled to overcome in sales campaigns.

Despite all of the data and statistics that validated the superiority of Boeing's 747SP the DC-10  proved a tough competitor to best.  Unlike the 747SP which had been specifically designed and optimized for very long range routes with limited demand, the DC-10 platform had been designed from the outset with flexibility in mind.  McDonnell-Douglas was able to optimize the aircraft to a variety of routes and mission requirements. The short range 10 series was an ideal aircraft for U.S. domestic trunk routes for airlines like United and American.  While the longer range 30 series had the endurance to fly trans-oceanic routes as well as intercontinental flights between Africa, Asia and Europe.  In all McDonnell-Douglas produced 446 aircraft across 9 different variants of the DC-10 through out its 18 year production run from 1971 to 1989.

A Comparison of 747SP, A300, DC-10 and L-1011 Deliveries from 1971-1989

Sales of Lockheed's long range L-1011-500 series were hurt tremendously by the airplanes significantly delayed development and entry into service due to engine maker Rolls-Royce's financial problems.  While competitors General Electric and Pratt & Whitney quickly developed uprated versions of their engines to power longer range versions of the DC-10, Rolls-Royce was slow to develop higher thrust variants of the RB211 for the L-1011.  This delay to market cost both Rolls and Lockheed dearly.  The first L-1011-500 aircraft did not enter revenue service with launch customer British Airways until May of 1979 a full three years behind the 747SP and seven years behind the competing DC-10-30 tri-jet.  By the time the L-1011-500 finally entered service the DC-10 had already captured a large portion of the market.  However despite its development problems with the L-1011 program Lockheed still managed to sell 249 airplanes during the course of the program's 13 year production run from 1972 through 1985.

By 1979 Airbus had also begun to make serious headway with the A300-B4, the long range variant of its A300 widebody twin jet.  Enjoying particular sales success in Asia with a landmark order for the airplane coming from Korean Air Lines.  This order served as the catalyst for other airlines in the region with Airbus booking new orders from Thai Airways, Singapore, Malaysia, Garuda Indonesia and China Airlines in short order.

Most countries in Asia had adopted ICAO's less restrictive 90 minute regulation regarding twin jet operations which allowed the A300 to operate unimpeded on routes throughout the region.  The A300's inroads in Asia further hurt the sales prospects of the 747SP, especially as this was one of the key markets targeted by Boeing full of major existing 747 operators.

Of the four widebody aircraft the A300 would eventually enjoy the greatest sales success.  Made possible by the FAA and ICAO relaxing restrictions on twin engine commercial jet transports in the 1980's and the formation of the ETOPS program to allow twin jets to prove their reliability and expand their reach.  Sales of the A300 remained steady while interest in the DC-10 and L-1011's began to flag after 1985.  With Airbus committed to producing new and improved models of the aircraft Airbus went on to sell 561 of the airplanes during the 33 years it was in production.

By this point the writing was on the wall, and Boeing began to realize that the SP just wasn't going to be the great seller they envisioned.  Despite the company's best efforts only forty-five 747SP aircraft were eventually built and delivered over the course of the airplane program's brief eight year production run from 1976-1982 and 1987.  The line was briefly re-opened in 1987 to produce one additional aircraft for the Government of Abu Dhabi.

747SP Customers with (Total Aircraft Ordered and Delivered) © Gregory Maxwell, 2014 
But even with limited success in the airline market the 747SP proved in one small but prestigious segment it was the only aircraft for the job.  The government VIP transport market which Boeing had targeted early in the aircraft's development turned out to be tailor made for the SP's capabilities.  For both small and medium sized countries the 747SP was an outstanding VIP transport, where its exceptional performance and range could be put to full use.  Many governments in The Middle East and Asia purchased the aircraft for use by their respective heads of state.

The 747SP provided the cachet that comes with being a member of the 747 club, but its size and price tag were more manageable for smaller governments than the larger 200B.  Three aircraft were purchased outright as VIP transports including the last aircraft built A6-ZSN in 1987, with a further 9 airplanes to date have been converted after being purchased on the second hand market.

It is easy to say given the 747SP's less than stellar sales that it was a failure, after all both McDonnell-Douglas and Lockheed sold far more trj-jets.  But from a cost perspective the derivative aircraft was relatively cheap for Boeing to design and build and it ended up just about breaking even for the company. The SP also allowed Boeing to retain key 747 customers and thwarted a number of potential sales of the DC-10 and L-1011.

For the small niche market that the aircraft was designed and built for there was no equal. You either had to buy a 747SP or loose high yield customers to your competitor who could get there faster and nonstop. Ultimately neither the DC-10 or L-1011 came close to matching the 747SP's incredible top end range and payload uplift.

At the end of the day, Boeing was probably a little over ambitious in its sales projections but the airplane did exactly what it was designed to do and continues to soldier on today.  Perhaps there is no greater testament to the aircraft's tremendous capability an appeal than the fact that of the 45 aircraft built 18 (almost half) are still in active service today.

Great Airliners Volume 3 - Boeing 747SP by Brian Baum
Airliner Tech Series Volume 6 - Boeing 747-100/200/300/SP by Dennis R. Jenkins
747SP Website
Boeing 747 Website


  1. I really enjoyed you 747sp celebration here. Lots of nice art Nd specs makes for a nice read and future reference.

  2. Outstanding article. Thank you for that.

  3. Great article! The one and only time I've had the opportunity to see the curvature of the earth was from the cockpit of one of Qantas Airlines' two SP's on an SYD/SFO flight back in '85 I think. I was 17 at the time and my uncle Patrick who was a flight route planner of some sort at the time, and working for Qantas in Sydney, had arranged a surprise invitation for me to spend about an hour in the cockpit with the flight crew. We were high over the Pacific Ocean, somewhere between Hawaii and California and I remember the views vividly as the sun was just rising at our 2 o'clock position, and the sky below us was light blue and lavender maybe, and above us it was dark as night. With about a 180° view of the horizon from the flight deck, I was awe struck to see our world from the perspective of an astronaut. We were "cruising at max speed and altitude with a strong tailwind", to paraphrase what the Captain explained to me. What an amazing experience that was for me. That one hour trumped anything else I did during the four weeks I spent in Sydney and New Zealand with my family. This airplane absolutely was, and still is, one of a kind. Thank you for this informative and detailed article!

  4. I was one of the volunteers to do the evacuation test at Paine Field. Even though it was a test, the stewardesses didn't treat it like that. I learned what happens during an evacuation. The cabin crew is trained and trained and trained. They snap to. Those friendly hostesses who welcome you aboard have their vocabulary reduced to two words: GET OUT!And jumping out the door into a pitch dark factory, I mean straight out and thunk! I hit the slide and got rug burn on my leg. But if I'm ever in a real evac I won't be in shock.

  5. Fantastic and highly informative article ! ! ! I was lucky enough to fly in an SP near the end of July 1977 from LAX to Tokyo. Though a long flight (10.5 hrs.), it was smooth and comfortable. After all these years, is it possible to find out exactly which SP I flew in? I mean, as to when it was built.

  6. I worked for the Saudi Arabian oil company Aramco in the late 70's and early 80's. Twice a week they would fly a Pan Am charter 747SP nonstop from Houston to Dhahran, Saudi Arabia, to transport their new employees and their families, along with business travelers. Returns would include business travelers, and employees on vacation or leaving the company. The plane was configured into all first class seating, holding about 100. The plane may have been a combo, as they would even ship entire households of furniture back for returning employees (a 4000 lb shipment was billed at $20K in 1982!). Flights took about 12 hours to SA, about 13- 14 return to Houston. Return flights would leave at midnight, and arrive in Houston about 8 am, ready for the day! My friends were on one that had an engine fire on takeoff from Saudi, with flaming pieces of engine falling off the plane. They circled the Gulf for an hour or more, dropping fuel so they would be light enough to land. They were told that this was the most fuel that had ever been jettisoned on a flight. They could smell it in the cabin. It was a very neat looking plane. I think Pan Am also flew them Riyadh to NYC.

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  9. Amazing article. Thank you. I learn more about why and how the airline industry has evolved into what we see today than anywhere else. Just starting ATP training. Sad that it’s so unlikely I’ll ever have a chance to operate any of the queen’s variants.

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The author is an independent aviaion consultant with 7 years of industry experience and holds a Masters Degree in Aviation Safety from Embry-Riddle Aeronautical University

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