Original Date: 08/07/1995
Revision Date: 01/18/2007
Best Practice : Electrical Power System Integration
Lockheed Martin Tactical Aircraft Systems (LMTAS) addressed a problem of on-board avionics digital computers on the F-16 aircraft improperly handling bus-switching transfers. Although these computers were designed and qualified to the electrical power requirements of MIL-STD-704A and met the requirements when tested separately, anomalies were experienced when integration of the total aircraft electrical system was attempted.
LMTAS determined that although these transfers were within the limits of MIL-STD-704A, qualification testing was done at the model worst-case level for analog electronics (0 volts, 50 msec). This qualification testing did not account for bus transfers that were faster than the worst case scenario. This faster electrical transfer rate would cause multiple power-up, power-down conditions, and would cause corruption of the computer software, creating the integration problems.
Lockheed Martin therefore expanded the test requirement for new equipment specifications to provide more detailed information on test method and parameter selection. This specification requirement now verifies specified operation for total power capacity consumed, steady-state voltage limits, normal and abnormal transients (multiple test points throughout each allowable envelope), and power transfers (multiple test points). Besides expanding the test requirements, LMTAS built a fully instrumented test bench to simulate and duplicate all F-16 aircraft electrical systems. This test bench can duplicate different aircraft power generation systems and vary the performance of each generation system within its design parameters. The use of this test bench is offered to all prime groups and suppliers for electrical system integration testing.
By duplicating the aircraft power system and its variances, specifying test conditions and parameters, and then integrating the complete electrical system, LMTAS has identified MIL-STD-704A non-compliance issues during hardware development and qualification testing. This has allowed the company to eliminate cost and schedule impacts created when non-compliance is identified after hardware delivery. Electrical system integration can be accomplished in a laboratory environment before a production break-in, eliminating corrective actions needed after initial aircraft production and field use.
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