Page:NTSB Report, 1967 Lear Jet crash.pdf/18

- 15 - contact resulted from the aircraft's descent below the minimum radar reception altitude of 2,100 feet. The severe degree of aircraft disintegration precluded a determination of the exact source of the electrical difficulty However, the AC electrical system is essentially a single bus concept, Since the primary and secondary busses are wired together in series through the bus the breaker. This permits a short in any AC component to fail both the main inverter and then the standby inverter as it in turn is selected. Such an electrical problem and subsequent attempt to rectify the problem is indicated in the 360-degree heading displayed on the BMI. The heading conforms to neither the 260-degree heading of the other instruments nor the 335-degree heading at impact, and is probably the result of some combination of bus and circuit breaker isolation during trouble-shooting, or a partial restoration of power prior to the final AC power failure in the final maneuver.

2.2 Conclusions

(a) Findings  The crew was properly certificated. The aircraft was properly certificated, and had been released for test flight only. There were inadequacies in quality control, inspection, and flight testing during the major modufucatuons of the aircraft. The gross weight and center of gravity were within allowable limits. There was turbulence at the flight's cruising altitude. 