Seaboard 747F with P&W JT9D-70A Engines

jt9d-70a.jpg Photos courtesy of Capt. David O. Hill 

by Capt. Ken Kahn

Seaboard was the first airline to order the Boeing 747F. At that time, all 747s, except for those with Rolls‑Royce engines operated by a handful of foreign airlines, had Pratt & Whitney (P&W) engines. With a maximum takeoff weight (MTOW) of 820,000 pounds, the 747F was designed for engines capable of 53,000 pounds of thrust. The engine proposed by P&W for the 747F was the JT9D‑70A. Its nacelle, designed by Rohr Inc., was designed to fit DC‑10s and Airbus A300s, as well as 747s. It was thought that the common nacelle concept would have wide appeal to airlines which operated to or three of these types of aircraft. In addition, some of the engine accessories were relocated in the nacelle to facilitate maintenance.

The problem with the P&W JT9D-70A engine was that it would not be available until approximately one year after the first airplane, N701SW, would be otherwise available. General Electric (GE), however, had a 53,000‑lb‑thrust engine (CF6‑50) that would be available in time. Seaboard was interested but concerned that having unique engines would make it impossible to borrow parts or spare engines in case of a failure. GE was very eager to break into the market for 747 engines and made a tempting offer to Seaboard. They would arrange to deliver parts and/or engines to wherever Seaboard needed them and reimburse Seaboard for lost revenue due to down time. Seaboard was only stopped from selecting GE engines by another tempting offer from P&W. They proposed providing smaller engines at their expense for the first aircraft, paying for maintenance on those engines until the larger engines were available, and reimbursing Seaboard for lost revenue due to the reduced payload, approximately 20,000 pounds, resulting from the smaller engines. Seaboard accepted P&W's offer. For more than a year, Seaboard collected payments for 20,000 pounds of freight, even on flights when the load was not limited by the smaller engines.

N703SW is seen here with the Pratt & Whitney JT9D-70A engines. With 53,000 lbs. of thrust, it was the most powerful jet engine in the world at the time of its introduction into commercial service. It first appeared on 703's sister-ship, N702SW, in May 1976. N702SW was the test-bed aircraft used for certification of these engines. The nacelle's sleek profile and elliptical cowling sometimes caused it to mistaken for a GE engine. Click here for another view of this engine. This photo, showing Capt. Ed Foster standing in the inlet, gives an indication of the size of the engine.

The JT9D-70A was very reliable in service. In the end, however, the common nacelle and the JT9D‑70A failed in the marketplace. The airlines that operated 747s wanted the bigger engines in the sort of nacelle they already had. P&W repackaged the accessories and designated that version the JT9D‑7Q. It had slightly less drag, resulting in lower fuel consumption. It also had more ground clearance, decreasing the possibility of striking the runway with an inboard nacelle during crosswind landings. When the Seaboard aircraft passed to FedEx and FedEx tried to sell them, they found few customers due to the unusual engines. GE eventually did capture a significant share of the market for 747 engines.

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