Narrative:Flight 542 departed the ramp at Houston at 22:37, 22 minutes behind schedule. The delayed departure was due to a mechanical discrepancy involving No. 3 generator. This generator was inoperative on arrival of N9705C at Houston. Prior to departure from Houston the Nos. 3 and 4 voltage regulators were interchanged. The estimated time en route to Dallas was 41 minutes.
The flight was given an IFR clearance which was to the Leona omni, via Victor Airway 13 west to the Gulf Coast intersection, direct to Leona, to maintain 2,300 feet altitude to Gulf Coast, then to climb to and maintain 9,000. At approximately 22:40 the flight was cleared for takeoff and at 22:44 the crew reported airborne.
After takeoff Houston departure control advised that it had the flight in radar contact and requested it to report when established outbound on the 345-degree radial of the Houston omni. Flight 542 complied and subsequently was cleared to 9,000 feet and advised to contact San Antonio Center upon passing the Gulf Coast intersection.
At approximately 22:52 Flight 542 reported to San Antonio Center as being over Gulf Coast intersection at 9,000 feet. The flight was then issued its destination clearance to the Dallas Airport and it was cleared to climb to its cruising altitude of 15,000 feet. After the Electra had passed Leona at 23:05, the crew contacted company radio with a message for maintenance, advising that the generators were then OK but that there had been insufficient time for maintenance to insulate the terminal strip on No. 3 propeller at Houston and it would like to have it done in Dallas.
At 23:09 the left wing and the No. 1 gear box propeller separated. The horizontal stabilizer then broke up under the impact of parts coming from the wing; wing planking from the right wing tip came free; the No. 4 powerplant tore loose; and the right wing outboard of No. 4 separated. All of these events happened in a short period of time. Somewhat later, at much lower altitudes, the fuselage broke in two separate portions at a point about halfway back near fuselage station No. 570.
PROBABLE CAUSE: "Structural failure of the left wing resulting from forces generated by undampened propeller whirl mode."
Loss of control
» ICAO Circular 64-AN/58 (51-61)