Boeing - 707-320C
The Boeing 707-300C is a convertible passenger/freighter aircraft which is essentially a 707-300B with a 2.31 X 30.4m forward cargo door, a strengthened floor and landing gear. In comparison with the 300B the operating empty weight of the aircraft is increased by 3000 kg but this allows the maximum structural payload to be increased by 13,000 kg when operating in the freight role.
In addition the maximum landing weight is increased by 18,000kg which considerably increases operational flexibility. This proved so attractive to operators that the 707-320C became the best selling version of the 707 with a total of 305 being ordered by airline operators. Some operators ordered their aircraft as dedicated freight aircraft, which allowed a further increase in maximum payload of 5,800kg as the empty weight of the aircraft was reduced by the same amount due to non-provision of the passenger/freight conversion capability.
The first aircraft was delivered to Pan American on 2 May 1963 and was the first of 34 707-300Cs for the airline; other operators included American Airlines with 37 aircraft and Northwest Orient Airlines with 26.
Other international carriers such as Qantas (21 aircraft) and Lufthansa (6), ordered the 300C and production of the 707-300C continued until 1979 when the last aircraft was ‘delivered’ to Boeing and converted into the only 707-700. The 707-700 was powered by CFM-56A turbofans, and was primarily intended to prove the engine on the 707 airframe for military applications and to offer a more efficient, economic and environmentally friendly 707.
No orders were forthcoming from commercial operators and the 707-700 was restored to the standard 707-300C configuration and delivered to the Moroccan Government in March 1982. The CFM-56A installation on the 707 airframe however proved successful, and as a result later E-3 airframes and the KE-3 and KC-135 tankers were powered by the CFM-56A.
The 707-300C’s capabilities proved attractive for a number of military missions including in-flight refuelling and electronic surveillance and 31 were ordered from the production line to fulfil military or governmental orders with others being acquired as they were retired from airline service. The 707-320C airframe was also selected as the airframe component of surveillance and communications systems, such as the E-3 AWACS and E-6 Mercury and production of the 707-300C airframe for these systems continued after commercial aircraft production had ended. A total of 92 airframes were produced for these roles comprising of 68 E-3, 16 E-6 and 8 KE-3 tankers with an undisclosed systems capability.
The final 707 airframe produced was an E-3D AWACS for the Royal Air Force which was delivered on 12 May 1992.
The implementation of FAR Part 36 Stage 3 and ICAO noise legislation saw the production of hush-kits for the 707-300C to enable continued operation and a number of aircraft were modified,but only small numbers remain in service.
Lloyd Dunning-Mitchell
