Profile – Boeing’s Heavy Jet Heritage

But continued testing of the Dash 80, structural testing of the 707 airframe on the ground and a very strong sales pitch by Boeing were aimed directly at converting the somewhat apprehensive airline community into Boeing 707 buyers. The 367-80 first flew on 15 July 1954 and within three months Boeing had been awarded the USAF jet tanker/transport contract, leading to the KC-135 family, a purchase which in itself helped give the 707 an even firmer standing in the marketing stakes. However it was not until 13 July 1955 that Boeing was given official clearance to build commercial variants of the Dash 80 – the Model 707 – concurrently with KC-135 production. Once this clearance was granted, the Boeing sales pitch was stepped up and the 367-80 entered a new, even more hectic round of flight testing and concept proving, aimed at convincing airlines that the 707 would be a safe, reliable means of transportation.

During 367-80 flight testing, several record breaking and publicity achieving flights were performed, including the famous Lake Washington roll by test pilot Tex Johnston and a record trans-USA flight in 1955. More typical of publicity flights however was the press demonstration of 11 March 1957, when the Dash 80 was flown non stop from Seattle to Baltimore in a time of 3 hours 48 minutes, at an average speed of 531kt (984. 3km/h) over a route typical of that at which the 707 was aimed. However by this time Boeing had already received its first 707 orders, the then industry giant Pan American being the 707 launch customer with an order for 20 aircraft placed on 13 October 1955. However, though the 707 program was therefore well on its way to revolutionising transportation, it did not by any means immediately hold the key position in the jetliner marketing stakes.

Rival manufacturer Douglas officially commenced full scale development of its own jet transport, the DC-8, on 7 June 1955 as a direct challenge to the 707. News of the DC-8 program reached Boeing the following day, giving the 707 team some reason to be concerned. Such was Douglas’ reputation as a commercial aircraft manufacturer (its DC-2, -3, -4, -6 and -7 families were all successful airliners, taking Douglas from the mid 1930s through to the mid 1950s and seemingly cementing its reputation in the commercial airliner market) that even though it had no prototype flying (DC-8 flight testing did not commence until 30 May 1958) airline interest in the proposed new aircraft was immediately high. The mere promise of a successful new airliner from Douglas was enough for Pan American to also become the DC-8 launch customer, with an order for 20 aircraft placed on the very same day that it placed its first order for twenty 707s! Surely the ultimate each way bet.

Douglas continued to attract customer interest by promising higher payloads and more powerful engines, amongst other advantages for both airlines and passengers. Boeing recognized the threat from Douglas and even considered substantially redesigning the 707 to make it bigger and longer ranging, however common sense prevailed and it was decided to press on with the design as was to take full advantage of the healthy lead held by Boeing at that time. But then United Airlines, impressed by the additional range being offered by Douglas, ordered 30 DC-8s two weeks after PanAm (Douglas’ second DC-8 order, Boeing still had only the PanAm order) and Boeing were forced to come up with a new strategy. It announced a new 707 variant, to be called the Intercontinental 707, which would offer greater range and a fuselage stretch to provide greater passenger capacity. Thus even before the first 707 was flown, new variants were actively being developed to enhance the 707’s flight capabilities.

The challenge set by Douglas was not destined to last long. During 1957 and into 1958 the 707 and DC-8 competed head to head for orders, and for a while the DC-8 even appeared to be the more successful. By the time the first 707 was delivered to launch customer Pan American however, the threat posed by the DC-8 had been overcome and more and more airlines were ordering the Boeing product. Initially this was primarily because of the program lead held by Boeing, howeverit was soon recognised that the DC-8 was less flexible in meeting airline requirements than the 707 family, so sales of the Douglas aircraft never met expectations, though sales did reach a relatively healthy 556 (361 less than the commercial 707 variants) before production ended in 1972. The only other US contender for the heavy jet transport market was the Convair 880, which ended production at just 65 (37 improved 990s were also built). The DH Comet 4 could barely be rated as a threat to the Boeing 707 whilst the VickersVC10 came along too late to make any . I impression on the market.

First deliveries

The first Boeing 707, designated 707-120, was rolled out of the Renton factory on 28 October 1957. Appropriately registered N707PA, this first production 707 was soon forced to undergo a demanding series of flight tests to prove to the US Civil Aeronautics Administration (now the Federal Aviation Administration) that the aircraft was safe, reliable and suitable for passenger transportation. This was achieved almost a year later when on 23 September 1958 the FAA granted the 707 its type certificate, clearingthe way for fullscale production and allowing Pan American to plan its first 707 services.

Substantial testing of the first production 707 was necessary because it was indeed the first of a new type. Although, the 367-80 is generally regarded as the 707 prototype, it was really no more than a one-off test aircraft and was never intended to go into commercial production. Though the 707 was based on the Dash 80, it incorporated several new features which separated it from both the 367-80 and the KC-135 family. For instance, to facilitate passenger carriage the 707 fuselage was widened by four inches and lengthened by 1Oft, and of course the row of windows had to be added, which perhaps made the most obvious external difference to the military tanker. The slightly larger fuselage diameter meant that Boeing could not utilise common jigs for construction of the KC-135 and 707.

The KC-135 was constructed with a “safe life” philosophy, using 7178 aluminium alloy in construction and giving a better strength-to-weight ratio. The FAA, however, required that the 707 be constructed under a “fail safe” philosophy for passenger transportation,this being required for the aircraft to meet stricter civil safety regulations.

The span of the KC-135 and 707-120 remained the same, though with the 707-320 series intercontinental airliners wingspan increased considerably, by at least 4. 5m. The 707 also featured air intakes at the root of its engine pylons, these serving the turbo-compressors, which were driven by engine bleed air to pressurise the cabin. The KC-135 on the other hand utilised engine bleed air directly to pressurise the cabin, so the intakes were not necessary.

The historic inaugural 707 airline service occurred on 26 October 1958 when Pan American flew 111 passengers from New York to Paris onboard their recently delivered 707-120, N709PA. By this time the 707 had already attracted healthy sales, from such giants as Pan American, American Airlines, Continental, TWA, Lufthansa, Air France, BOAC (a blow to the UK aviation industry given that BOAC were at the time the principal DH Comet user, and intended as the main operator of British jet transports then under development) and, although not a giant, of interest to the Pacific Rim nations, Qantas, who was in fact the fifth 707 customer and the first non US buyer.

It soon became obvious to airlines and passengers alike just what the new generation of jet transports meant for travel. The earlier DH Comet had been a great step forward in aircraft travel, however it featured a fuselage capacity no bigger than the fleet of turboprop powered airliners then in service, so Comet services were mostly restricted to first class passengers only. On the important transatlantic routes, the Comet did very well carrying first class passengers at higher speeds and in a greater degree of safety, however only until the 707 took over soon after it entered service With its larger fuselage and superior performance the 707 immediately became popular with passengers, though initially, like the Comet, 707 travel was restricted to first class travellers (121 could be carried) for some months until sufficient numbers had entered service. Passengers and crew alike could well appreciate the advantages of flying at heights well above the weather conditions which older propliners would had to have flown through, and PanAm soon developed a healthy lead on the transatlantic network. Flights were smoother, faster, and undoubtedly much safer. And with the capaciousness of the 707 (about twice the passenger capacity of the older Constellations) flying was becoming an option for more and more travellers. Just as the 707 fast killed off competition from propliners on most of its routes, it also proved to be the final death knell for the ocean going passenger liners which up until even the mid 1960s plied the waves with travellers rather than holiday-makers. To say that the 707 revolutionised travel is therefore no exaggeration.

707 described

The first 707 variant to roll off the production line, the 707-120, was available in two distinct sub-variants, the standard fuselage length (see 707-120 Specifications table) and a special shorter fuselage variant, which significantly was ordered only by Qantas. The -120 was intended primarily for domestic routes, however it was very soon adopted for over ocean ops, first by PanAm on its transatlantic routes. Powered by four 13,000lb thrust P&W JT3C-6 turbojets, standard accommodation was typically 121 first class passengers or 179 economy. With the advent of longer ranged intercontinental variants most -120s were relegated to domestic routes and several -120 orders were changed to later model orders, however 63 were constructed for several customers The short fuselage 707-120 version purchased by Qantas was a prime example of Boeing working hard to attract sales by ensuring its aircraft best suited customer requirements. Despite some strong behind-the-scenes political presure to “buy British”, Qantas had narrowed down the contenders for its first jet airliner to the Douglas and Boeing products, and then in September 1957 announced the order of seven 707s valued at £18,800,000. The Boeing aircraft had been chosen because it was considered more flexible and better suited to Qantas’ somewhat unique operating requirements. Boeing went out of its way to design the 10ft shorter fuselage variant so that Qantas could operate the aircraft on its trans-Pacific services. Sydney Airport at that time featured a maximum runway length of only 2,409m (7,898ft), only just adequate to cater for the new jet transports and drastically in need of lengthening, while Qantas’ Pacific stopover destinations similarly had short runways. The shorter fuselage was needed to give Qantas 707-138s additional range and better runway performance, while the longer routes typically flown by Qantas meant that passenger capacity did not have to be as high as many other airlines’ aircraft.

Besides the Qantas 707-138s, another example of Boeing’s efforts to satisfy customer requirements was the -220 variant, of which five were built for US airline Braniff. The aircraft were powered by more powerful 15,800Ib thrust JT4A-3 engines for slightly better takeoff performance, however no fur ther orders for this option were forthcoming.

The 707-138 led directly to the development of the very similar Boeing 720, which entered service with United Airlines on 5 July 1960 and was aimed directly at US domestic operators. The 720 was a new design from weight and structural strength standpoints, however it was so closely related to the 707-120 that it featured the same flightdeck and cabin interiors and systems components, and most parts and spares were interchangeable. Length of the 720 was reduced to 41. 7m (136ft 10in), and the airframe featured several aerodynamic modifications. The most important change was a refinement to the wing leading edge, which increased the angle of sweepback and decreased the thickness/chord ratio, with consequent improvements in takeoff performance and cruise speed. Major weight savings were achieved by lightening the 720’s structure by reducing the standard fuel capacity. The aircraft proved to be a quite successful, mainly domestic airliner, with 65 720s and 89 of the turbofan powered 720Bs sold.

The introduction of turbofan engines were to further boost the 707-120’s performance. Development of the Pratt & Whitney JT3D turbofan engines led to the 707-120B and 720B being offered soon after the program got underway, with the first flight of the -120B sub-variant taking place on 1 March 1961. Some 78 -120Bs were built, while most of the 63 -120s (including all seven Qantas -138s) were returned to Boeing to be modified to B standard. The turbofan was a significantly improved engine and when combined with the 720 type wing refinements and other minor modifications produced substantially improved performance figures: max cruise speed for 707-120 496kt (919km/h), -120B 537kt (995km/h); econ cruise -120 477kt (884km/h), -120B 484kt (897km/h); rate of climb -120 2,400ft/min, -1208 5,050ft/ min; service ceiling -120 37,500ft, -120B 42,000ft; max range -120 4,040nm (7,485km), -120B 5,400nm (10,000km).

Alongside the -120 series aircraft came the longer ranged 707-320 Intercontinental variants, the first of which flew on 11 January 1959 and presented a direct challenge to Douglas’ promise of a longer ranged, higher capacity intercontinental DC-8. The -320 featured a fuselage stretched two metres to 44. 35m (145ft 6in), an increased wingspan of 43. 41m (142ft 5in), as well as a number of aerodynamic refinements. Several engine options were offered, these being the Pratt & Whitney 15,800lb thrust JT4A-3 and -5 turbojets, 16,800Ib thrust JT4A-9 or 17,500Ib thrust JT4A-11 turbojets. These enabled the aircraft to carry up to 189 passengers 5,750nm (10,655km), and proved quite popular, with 69 being sold.

An additional engine option for the aircraft was the RollsRoyce Conway Mk 508 turbojet, rated at 17,500Ib thrust. With these engines the aircraft was designated 707-420, the only real difference to the 707-320 being the engine choice. BOAC were the first to choose this engine choice, mainly because the Conway was a British product and the decision to purchase the 707 rather than a British aircraft was politically sensitive enough as it was, though several other airlines opted for the -420. Thirty seven were built, going to BOAC (19),Air India, Lufthansa, VARIG, EIAI and Cunard-Eagle. As with the -120 series, turbofans were soon offered as an option for the -320. Thus the -320B was offered with P&W JT3D-3 or -3B turbofans, each rated at 18,000lb thrust, fitted with double thrust reversers and offering increased performance figures. Other refinements to the aircraft included new leading and trailing edge flaps, low drag wingtips and other minor modifications such as a wingspan increase of a further one metre. The -320B entered service with Pan American in June 1962, and ultimately 174 rolled off the production line, with further -320sbeing returned to Boeing to be updated to B standard. But by far the most popular and best selling of the 707 family was the -320C Convertible, the final intercontinental variant to be offered. The -320C was developed in response to requests for a 707 freighter. Boeing had initially designed the Model

735-320B, a designated freighter based on the 707-320B and capable of carrying a 36,320kg (80,000lb) payload, however development of this variant did not proceed. Instead the 707-320C was offered with the ability to interchange roles, so the aircraft could be configured to carry all passenger, all cargo or mixed pax/cargo loads. The -320C was powered by P&W 19,000lb thrust JT3D-7 turbofans as well as several minor airframe modifications for improved performance (see 707-320C Specifications). It featured a 2. 31m x 3. 4m forward cargo door and a Boeing developed cargo loading system, using either pallets or containers. Cargo space comprised 228m3 (8,074cu ft) on the full upperdeck and 48m3 (1,700cu ft) in two lower deck holds. Accommodation for 202 passengers could alternatively be provided. As had almost become custom, Pan American introduced the new variant to service in June 1963. Some 337 were ultimately built, and it was the last commercial variant to roll off Boeing’s Renton production line for delivery on 30 January 1978.

Other 707 variants, usually incorporating fuselage stretches and ne’I’. ‘ engine choices, were from time to time proposed, up to the Boeing Model 707-820. However these were not proceeded with, and the 727, 737 and 747 took over the production lines to fulfil airline requirements. When the final -320C was delivered, it was the last of 917 7o7/720s completed, of which 878 were sold to commercial customers and the remainder to various military forces or governments, the US Air Force having for instance purchased four as VC-137s. The airframes delivered were 63 707-120s, 78 -120Bs, five -220s, 69 -320s, 174 -320Bs, 337 -320Cs and 37 -420s, as well as 65 720s and 89 720Bs. Additional sales of specialist military aircraft (most noticeably the E-3 and E-6) have taken total 707 airframe orders to 1,010. The military derivatives will be described next issue.

Update programs

The 707 has been the subject of many update programs, the first of course being that of replacing the original turbojets with turbofans to produce B variants. However in more recent years new modification programs, most involving the replacement of engines and/or the updating of flight systems, have been introduced to enable the aircraft to remain in service worldwide, though few airlines now use the 707 in a passenger configuration.

In 1979 Boeing fitted GE/SNECMA CFM56 turbofans to a test 707, planning to offer an update program known as the 707-700 for commercial and military operators if interest was high. However the program did not proceed, though the CFM56 was adopted by the US Air Force to update a large number of its KC-135 fleet to KC-135R standard.

A number of companies worldwide now offer update programs for the 707, of which one of the most successful is that of Comtran, which offers a fully updated aircraft with hushkitted engines enabling it to meet Stage 2 noise regulations, a modern, EFIS equipped cockpit and various other refinements suited to both freight operators and charter organisations. The 707 is proving to be well suited to such operations, and should remain in service for many years to come. Those aircraft which survived the 1980s purge which resulted in several hundred airframes being scrapped for their engines by the US Air Force for their KC-135E update program remain in demand, though numbers are gradually falling. Of the 917 airframes built, about 300 are estimated to be still in service with various civil and military operators worldwide.

And so, though well past its prime, the 707 continues to ply its trade in the skies above. No doubt it will do so well into the next century, being updated and maintained as freighters and specialist aircraft for as long as life remains in its aging but solid airframe