Boeing 747 Electronic Engine Control (EEC) boeing 747 pilot training course

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Electronic Engine Control (EEC)

Each EEC has full authority over engine operation. The EEC uses Thrust lever

inputs to control forward and reverse thrust. The EEC has two control modes:

normal and alternate. In both normal and alternate modes, the EEC uses N1 RPM

as the controlling parameter for setting thrust.

The EEC calculates an N1 value between idle and maximum N1. Maximum N1 is

the maximum allowable thrust available from the engine. The calculated N1 is

compared to actual N1 RPM. The EEC commands the fuel metering unit to adjust fuel flow until actual N1 equals calculated N1.

EEC Normal Mode

In normal mode, EEC sets thrust by controlling N1 based on Thrust lever position.

N1 is commanded by positioning the Thrust levers either with the autothrottles, or by the flight crew.

When the engine is stabilized, EEC keeps thrust constant independent of outside

air temperature and pressure. The EEC adjusts thrust for changes in nacelle and

wing anti-ice and airplane pressurization bleed requirements. This allows a fixed

Thrust lever position throughout a climb.

Maximum N1 represents the maximum rated thrust available from the engine. The EEC continuously computes maximum N1. Thrust is limited to maximum N1 at the full forward Thrust lever position. Maximum thrust is available during any phase of flight by moving the Thrust lever to the full forward position.

EEC Alternate Mode

The EEC uses alternate mode as a backup to normal mode. If EEC detects a fault

and can no longer control the engine using the normal mode, it transfers control to alternate mode. Alternate mode can also be selected manually using the EEC Mode switch.

Alternate mode does not provide thrust limiting at maximum N1. Maximum N1 is

reached at a Thrust lever position less than full forward. Thrust levers must be

adjusted to maintain desired thrust as environmental conditions and bleed

requirements change.

Alternate mode provides equal or greater thrust than normal mode for the same

Thrust lever position. Thrust does not change when EEC transfers control from

normal mode to alternate mode. Thrust increases when alternate mode is selected

manually. When thrust is greater than idle, the Thrust lever should be moved aft

prior to manually selecting alternate mode so thrust does not exceed maximum N1.

If control for any EEC transfers from normal to alternate, the autothrottle

disconnects. The autothrottle can be activated after all EECs are manually

transferred to alternate mode.

EEC Idle Selection

The EEC selects minimum idle or approach idle. Minimum idle is a lower thrust than approach idle. Approach idle is selected in flight when:

• nacelle anti–ice is ON

• flaps are in landing position

• Continuous Ignition switch is ON

• during thrust reverser operation

Approach idle decreases acceleration time for go–around. Approach idle is

maintained until five seconds after touchdown, when minimum idle is selected.

EEC Overspeed Protection

At thrust settings above idle, the EEC monitors N1 and N2 RPM to prevent rotor

overspeed. If a rotor approaches overspeed, the EEC commands the fuel metering unit to reduce fuel flow to keep rotor speed from exceeding the operating limit even though the Thrust lever is commanding more thrust.

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