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:
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.
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.
