To prevent excessive structural loads from increased Mach at higher altitude, flap extension above 20,000 feet should not be attempted.

Flap and Slat Sequencing

LE devices and TE flaps are normally extended and retracted by hydraulic power from System B. When the FLAP Lever is in the UP detent, all flaps and LE devices are commanded to the retracted or up position. Moving the FLAP Lever aft allows selection of flap detent positions 1, 2, 5, 10, 15, 25, 30 or 40. The LE devices deployment is sequenced as a function of TE flaps deployment.

When the FLAP Lever is moved from the UP position to the 1, 2, or 5 position, the TE flaps extend to the commanded position and the LE:

• Flaps extend to the full extended position and
• Slats extend to the extend position.

When the FLAP Lever is moved beyond the 5 position the TE flaps extend to the commanded position and the LE:

• Flaps remain at the full extended position and
• Slats extend to the full extended position.

The LE devices sequence is reversed upon retraction. Mechanical gates hinder inadvertent FLAP Lever movement beyond flaps 1 for one engine inoperative go-around and flaps 15 for normal go-around.

Indicator lights on the center instrument panel provide overall LE devices position status. The LE DEVICES annunciator panel on the aft overhead panel indicates the positions of the individual flaps and slats.

The Flaps / Slat Electronics Unit (FSEU) provides a TE flap load relief function which protects the flaps from excessive air loads. This function is operative at the flaps 30 and flaps 40 positions only. The FLAP Lever does not move, but the Flap Position Indicator displays flap retraction and re-extension.

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 40, the TE flaps:

• Retract to 30 if airspeed exceeds 163 knots
• Re-extend when airspeed is reduced beiow 158 knots.