Convair 990 Coronado 990

American Airlines asked Convair for an aircraft able to fly coast to coast non-stop — New York to Los Angeles against the wind — after Boeing had flatly refused. The airline wanted more capacity than the Convair 880 and 880M, the smallest of the first-generation US jet airliners. The design was known internally as the Convair 600 and was redesignated Convair 990 in the month of its first flight. Flight testing began on 24 January 1961.

The most visible change from the 880 was the set of large anti-shock bodies on the upper trailing edge of the wing, intended to raise the critical Mach number by reducing transonic drag. The larger inboard pods doubled as additional fuel tankage. Late in the design period Convair decided to carry fuel in the outboard pods too, but during the initial test flights the extra weight made the outboard engines oscillate under certain conditions. The pods were redesigned and shortened, which increased drag.

The engines changed as well: the CJ-805-23 carried its fan stage at the rear of the engine, unlike the Pratt & Whitney JT3D of its competitors, which had it at the front. It was a simplified, non-afterburning civil version of the J79 turbojet. Like most J79 derivatives, the CJ805 and CJ805-23 were smoky; secondary operator Spantax eventually refitted its engines with low-smoke combustion chambers in the 1970s.

Like the 880, the 990 incorporated a dorsal raceway on top of the fuselage housing the two ADF antennas and one VHF antenna.

The 990 did not meet the specifications promised and American Airlines cut its order accordingly. In level flight the maximum speed settled at Mach 0.84, short of the 0.89 guaranteed to the airline, because drag levels with the anti-shock bodies were far higher than predicted. Out of that came the drag reduction programme that produced the 990A.