Overview
All primary flight controls on the 747-400 are hydraulically powered with no direct mechanical reversion. Surfaces are powered by combinations of the four hydraulic systems (1, 2, 3, 4) to ensure no single hydraulic loss disables a primary control.
Architecture
<FlightControlsSchematic /> — surface diagram with hydraulic system color coding.Surfaces
| Ailerons | Inboard (low/high speed) + Outboard (low speed only) |
| Outboard Aileron Lockout | Locked at flap retraction (high speed) |
| Spoilers | 12 total — 4 ground-only + 8 flight (roll/speedbrake) |
| Elevators | Inboard + Outboard, both sides |
| Stabilizer Trim | 2 electric motors, primary (column wheel) + alternate switches |
| Rudder | Upper + Lower, independent power |
| Flaps | Triple-slotted trailing edge — 1, 5, 10, 20, 25, 30 |
| Slats | Leading edge variable camber + Krueger flaps |
Hydraulic Power Distribution
| Surface | Powered By | |---|---| | Inboard ailerons | Sys 1 + Sys 3 | | Outboard ailerons | Sys 2 + Sys 4 (locked above flap 1) | | Upper rudder | Sys 4 | | Lower rudder | Sys 1 + Sys 3 | | Inboard elevators | Sys 1 + Sys 3 | | Outboard elevators | Sys 2 + Sys 4 | | Stabilizer | Electric, alt = sys 2 + 3 | | Flaps | Hydraulic primary (Sys 1) + Electric alternate | | Slats | Hydraulic (Sys 4) primary + pneumatic alternate |
Flap Schedule
| Flap | Max IAS | Phase | |---|---|---| | 1 | 290 | Climb/Descent maneuver | | 5 | 270 | Takeoff | | 10 | 240 | Takeoff | | 20 | 230 | Approach | | 25 | 205 | Approach | | 30 | 180 | Landing |
Failures & Abnormals
If primary trim is jammed, attempt alternate trim switches. If both jammed, hold trim against forces; expect significant control forces.