The EEC is mounted on the right top side of the fan duct and exists of two computers (channel 1 & 2), where one is active and the other standby although they’re both operating and cross linked during normal operation. The EEC receives numerous environmental and engine input signals to calculate fuel and control outputs to operate the engine and identifies the engines thrust rating by a pre-selected identification plug. Doing so it heats up and needs to be cooled which is achieved by tapping off, and directing fan air to the EEC.
Normal power source of the EEC is an alternator mounted on front of the engine gearbox but is only valid when the gearbox (N2) reaches 15%. Before 15% N2, the EEC is powered by Transfer Bus 1 or 2 (eng 1 or 2) if available, and becomes energized when the Start Switch is placed to GRD or CONT or, when the Start Lever is moved to IDLE. A de-energized EEC is indicated by blank engine indication boxes on the upper and lower DU’s even when the EEC button illuminates a white ON, just indicating that the EEC is selected to the normal mode. In this case the only indication visible directly from the sensors are N1, N2, Oil quantity and the vibration indicator, all others are blank. So . . . during a battery start (emergency power), indications of EGT, fuel flow, oil pressure and oil temperature remain blank until the alternator reaches 15%.
On the aft overhead engine panel there are the two guarded EEC control buttons to select the EEC to the NORMAL mode of operation (white ON light), or the manual HARD ALTERNATE mode of operation (amber ALT light). An undispatchable failing EEC is indicated also on the engine panel by a ENG CONTROL light and will only illuminate when on the ground and the engine N2 >50%.
A little teaser . . . . the last indication on the engine panel are two REVERSER lights . . . when and how long do they illuminate amber during normal operation?
