E

	E-4B Project

The E-4B serves as the National Airborne Operations Center for the National Command Authorities. In case of national emergency or destruction of ground command control centers, the aircraft provides a modern, highly survivable, command, control and communications center to direct U.S. forces, execute emergency war orders and coordinate actions by civil authorities. The E-4B, a militarized version of the Boeing 747-200, is a four-engine, swept-wing, long-range, high-altitude airplane capable of being refueled in flight.

E-4B Airborne Command Post


	The E-4B secure internal communications system, controlled by an embedded processor coded in Ada, was excessively slow upon initialization. Jay Swindle was given the task to solve the problem. He found no explanation in the code function so he researched the solid state crossbar switch used in the hardware design. He discovered that the crossbar switch was several orders of magnitude slower than the circuitry controlling it but still several times faster than the embedded control code could execute. Delay statements, put in the initialization code in the belief that the hardware required it, were the root cause of the problem. He removed the delay code and optimized the timing of audio circuit connection tests. This resulted in test completion time of 80 seconds from a high of about 17 minutes.

	Another problem of the communication system was dropped and corrupted messages. This had been occurring for over 30 months and no explanation could be found in the software although it had been rewritten three times. Jay Swindle and Terry Henry (an expert from another company) decided to examine the hardware. In less than an hour's time after starting the examination of the embedded processor's schematic diagrams, Swindle and Henry independently discovered the root cause: improper dual ported memory administration. It was possible for the embedded processor CPU and the system communications processor (a MIL-1553 device) to write shared memory at the same time. When the hardware problem was corrected, messages were no longer corrupted or lost.