Alternate Extension
In the event that hydraulic system B fails, an alternate method of extending the LE devices
and extending and retracting the TE flaps is provided.
When using alternate flap extension the LE flaps and slats are driven to the full extended
position using power from the standby hydraulic system. In this case the ALTERNATE
FLAPS master switch energizes the standby pump and the ALTERNATE FLAPS position
switch, held in the down position momentarily, fully extends the LE devices.
Note: The LE devices cannot be retracted by the standby hydraulic system.
Leading Edge Device Improper Position or Skew
The FSEU (Flap/Slat Electronic Unit) monitors the TE flaps for asymmetry and skew
conditions. It also monitors the LE devices for improper position and skew conditions on
slats 2 through 7. If a flap on one wing does not align with the symmetrical flap on the other
wing, there is a flap asymmetry condition. A skew condition occurs when a TE flap or LE
slat panel does not operate at the same rate causing the panel to twist during extension or
retraction.
When the FSEU detects a LE device in an improper position or a LE slat skew condition,
the LE FLAPS TRANSIT light remains illuminated and one of the following indications is
displayed on the LE DEVICES annunciator panel:
- Amber TRANSIT light illuminated.
- Incorrect green EXT or FULL EXT light illuminated.
- No light illuminated.
There is no skew detection of the outboard slats, 1 and 8, or for the LE flaps. Slat skew
detection is inhibited during autoslat operations.
