This paper develops guidance algorithms suitable for 4D-trajectory-based airspace operations. A previous paper by the same authors proposed a 4D-trajectory-based operational concept for terminal area operations. The concept consists of ground-side automation for synthesis of 4D trajectories and flight-deck-side automation for tracking the 4D-trajectory clearances. Whereas the previous paper dealt with the ground-side automation, the current paper deals with the flight-deck-side automation. The guidance algorithms are part of the flight automation necessary to realize the 4D-trajectory-based operations. The guidance algorithm design is based on the principles of feedback linearization and pole-placement techniques from feedback control theory. 4D trajectories are assumed to be designed using lower-fidelity models such as Base of Aircraft DAtabase (BADA) by ground-side automation. The guidance algorithms in the flight-deck automation on the other hand use higher-fidelity models to track the 4D trajectories. The guidance algorithm computes pitch attitude and throttle commands necessary to continually track a 4D trajectory. Closed-loop simulations using the high-fidelity TSRV aircraft model obtained from NASA Langley indicate very good tracking performance with time-tracking errors less than 1 second. Simulations demonstrate robustness to wind and temperature uncertainties. The guidance implemented on a pair of aircraft also demonstrate the capability to maintain along-trail separation.