737 Flight Crew Operations Manual
Flight Controls -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 9.20.19
Flap Load Relief
The Flap Slat Electronic Unit (FSEU) provides a TE flap load relief function
which protects the flaps from excessive air loads. This function is operative at the
flaps 10, 15, 25, 30 and flaps 40 positions. The FLAP lever does not move, but the
flap position indicator displays flap retraction and re–extension.
When the flaps are set at 40, the TE flaps:
• retract to 30 if airspeed exceeds 163 knots
• re–extend when airspeed is reduced below 158 knots.
When the flaps are set at 30, the TE flaps:
• retract to 25 if the airspeed exceeds 176 knots
• re–extend when airspeed is reduced below 171 knots.
When the flaps are set at 25, the TE flaps:
• retract to 15 if the airspeed exceeds 191 knots
• re–extend when airspeed is reduced below 186 knots.
When the flaps are set at 15, the TE flaps:
• retract to 10 if the airspeed exceeds 201 knots
• re–extend when airspeed is reduced below 196 knots.
When the flaps are set at 10, the TE flaps:
• retract to 5 if the airspeed exceeds 211 knots
• re–extend when airspeed is reduced below 206 knots.
Autoslats
Autoslat operation is normally powered by hydraulic system B. An alternate
source of power is provided by system A through a Power Transfer Unit (PTU) if
a loss of pressure is sensed from the higher volume system B engine driven pump.
The PTU uses system A pressure to power a hydraulic motorized pump,
pressurizing system B fluid to provide power for the autoslat operation. (Refer to
Chapter 13, Hydraulics, Power Transfer Unit)
At flap positions 1, 2, 5, 10, 15, and 25 an autoslat function is available that moves
the LE slats to full extended if the airplane approaches a stall condition.
The autoslat system is designed to enhance airplane stall characteristics at high
angles of attack during takeoff or approach to landing. When TE flaps 1 through
25 are selected, the LE slats are in the extend position. As the airplane approaches
the stall angle, the slats automatically begin driving to the full extended position
prior to stick shaker activation. The slats return to the extend position when the
pitch angle is sufficiently reduced below the stall critical attitude.
September 26, 2013
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