Maintenance Tips | 737NG MCP Window Black Screen

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Applicable to the 737NG aircraft with Collins MCP panel installed:

When switching power on the ground, the Mode Control Panel (MCP) display window shows a black screen with no display, and the button indicator lights are off, but all switches and knobs function normally. After resetting the circuit breaker or turning off the entire aircraft, it returns to normal.

Incident Background

On a certain 737-800 aircraft, after boarding, the crew reported that the MCP display window was black with no display, the button indicator lights were off, but all switches and knobs functioned normally:

After turning off the entire aircraft, it returned to normal, and subsequent flight segments were normal.

Problem Analysis

Refer to 737NG-FTD-22-20001:

Collins Mode Control Panel (MCP-730) Display Blanking and Inoperative Push Button Annunciator Lighting During Airplane Power Transfers

The manufacturer studied this issue and found:

The condition is the result of the MCP internal power supply going into an under voltage/over current condition and is caused by abnormal airplane power transfers. More specifically, when an airplane power transfer event occurs on the ground, airplane power transients may occur. These transients momentarily cause a decrease in 28V DC power applied to the MCP, which may cause the MCP internal power supply circuitry to draw excessive current, tripping the MCP over-current circuitry hardware monitors and resulting in blank display windows and/or inoperative push button annunciator lights.

Should this condition occur, the MCP can likely be recovered when a power cycle is performed through the AFCS MCP DC 1 (C1044) and AFCS MCP DC 2 (C1047) circuit breakers.

The fault occurred due to abnormal power transfer of the aircraft, leading to an under voltage/over current condition in the MCP internal power supply. More specifically, when switching power on the ground, transient power changes in the aircraft may occur.

These transients cause a temporary decrease in the 28V DC power supplied to the MCP, which may result in excessive current draw by the MCP internal power circuitry, tripping the MCP over-current circuit hardware monitors, resulting in blank display windows and/or inoperative push button lights.

If this condition occurs, the MCP may return to normal operation after performing a power cycle through the AFCS MCP DC 1 (C1044) and AFCS MCP DC 2 (C1047) circuit breakers.

The manufacturer has released Collins SB MCP-730-22-6 Rev. 1 to implement internal hardware modifications to the MCP to help reduce the occurrence of this issue. Affected MCP part numbers:

Maintenance Tips

If you encounter a black screen on the MCP window during flight, and meet these conditions:

1. The aircraft has previously undergone a power transfer

2. All MCP window indicators are black

3. All MCP buttons have no light indication

4. All MCP knobs and switches are functioning normally (confirmed on PFD and ND)

You can try resetting the following two circuit breakers to restore the MCP to normal:

• P18-1 D5 = AFCS MCP DC 1 (C1044)

• P6-2 C3 = AFCS MCP DC 2 (C1047)

Recommended Reading:

• Maintenance Tips | Explanation of the Auto Throttle Pre-Position Light on MCP

• Common Fault Handling Cards for 737NG | Chapter 22 Auto Flight

• Operational Tips | Cockpit Window Clamping the Drain Pipe Causing Air Leakage Whistle

The End