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Direct Law
This is the lowest form of law, requiring multiple failures. There is a direct relationship between side stick deflection and surface deflection. Control sensitivity depends on airspeed. Changes in thrust and speedbrake deflection cause pitching moments. Auto trim and autopilot are not available and USE MANUAL PITCH TRIM is indicated on the PFD. There is no auto turn coordination or dutch roll damping. The α floor function is inoperative.
Causes
Most cases of triple failures.
- Loss of all 3 PRIMs.
- Loss of all 3 ADRs.
- Loss of 2 elevators (leaving only pitch mechanical backup, MAN PITCH TRIM ONLY on PFD).
- Loss of both engines and PRIM 1 inop.
- When reaching 100' on the approach in normal law or alternate law, the pitch law is modified to be a full authority direct law with no auto-trim.
- When ferrying an aircraft with the gear down, a failure leading to alternate law will actually trigger direct law.
Protections
None are available, although stall and overspeed warnings still work.