Lockheed L-188 Electra L-188A

The Electra grew out of a run of discarded projects. In 1951 Capital Airlines approached Lockheed for a turboprop airliner, designated YC-130, but no other carrier was interested and the design was dropped; Capital went on to order sixty British Vickers Viscounts. In 1954, with American Airlines interested in a twin, the idea resurfaced as the CL-303, a high-wing type for sixty to seventy passengers that was also shelved.

The following year American revised its requirement to a four-engine design for seventy-five passengers with 3,200 km range. Lockheed proposed the CL-310, low-wing with Rolls-Royce Darts or Napier Elands. The design met American's requirements but not those of Eastern Air Lines, which wanted longer range, a minimum cruising speed of 560 km/h and eighty-five to ninety seats. Lockheed redesigned the CL-310 around the Allison 501-D13 turboprop — the civil version of the C-130 Hercules' T56 — and stretched the airframe. That design, led by chief design engineer Lou Storey, was launched as the Model 188 with an order for thirty-five from American Airlines on 8 June 1955, followed by forty from Eastern Air Lines on 27 September.

The first aircraft took twenty-six months to complete, by which time Lockheed held orders for 129. The prototype, a Model 188A, first flew on 6 December 1957, two months ahead of schedule. The Civil Aeronautics Administration awarded the type certificate on 22 August 1958. The first delivery, to Eastern Air Lines, came on 8 October 1958, though the aircraft did not enter service until 12 January 1959.

Passengers on early aircraft complained of cabin noise forward of the wings, caused by propeller resonance. Lockheed redesigned the engine nacelles, tilting the engines up three degrees; the change went into the production line by mid-1959 and was offered as a modification kit for aircraft already delivered.

What followed was far worse: three aircraft were lost in fatal accidents between February 1959 and March 1960. After the third crash the FAA limited the Electra's speed pending investigation. Two of the crashes were traced to an engine-mount problem: the gearbox mounting cracked and the resulting loss of rigidity allowed whirl mode flutter — a gyroscopic precession phenomenon — in the outboard nacelles. When the oscillation was transmitted to the wing and its frequency became resonant with the outer wing panel, the motion grew until the wing tore off.

Lockheed funded the LEAP programme at its own expense, strengthening the engine mounts and the wing structure supporting them and replacing some wing skins with thicker material. Each aircraft spent twenty days in the shop. The reputational damage, however, was already done.

The documented Model 188A order split covers forty for Eastern Air Lines — the last five delivered as 188Cs — thirty-five for American Airlines, fourteen for National Airlines, twelve for Western Airlines, nine for Braniff, three for Ansett-ANA, three for Trans Australia Airlines, two for Cathay Pacific and one for General Motors.