The lateral-directional dynamic mode of an aircraft characterized by a non-oscillatory, slow divergence or convergence in bank angle and heading with negligible sideslip is known as the:

(A) Spiral mode

(B) Dutch roll mode

(C) Roll subsidence mode

(D) Short-period mode

Answer Key:

A

### 5-Stage Derivation & Analytical Solution: 1. **Stage 1: Modal Decoupling:** Lateral-directional roots consist of one pair of complex conjugates (Dutch roll), one heavily damped real root (roll subsidence), and one slow real root (spiral mode). 2. **Stage 2: Characteristics:** Spiral mode involves coupled yaw-roll divergence over long timescales. 3. **Stage 3: Selection:** Option A is correct.

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