Aircraft Electrical Systems: A320/A321 Briefing

 

The Hidden A320 Go-Around Logic That Could Save Your Life (Or Catch You Out)

A go-around is a startle event. By definition, it happens when things are not going to plan. You are tired, low on energy, likely in bad weather, and in a chaotic split second, your workload spikes as you transition from a stabilized descent to a high-energy climb. Standard callouts are made: "TOGA, Flaps." You monitor pitch, check thrust, confirm a positive climb, and retract the gear. But in that critical moment, a fundamental question arises: Who is navigating?

For years, the answer was 'you are, by manually pushing a knob.' But a critical logic update in the A320's software—the "NAV in Go-Around" modification—provides a new, automated answer. Understanding this system has profound implications for flight safety, but it also contains a critical exception that every pilot must know.

1. The Automation That Fixes a Critical Safety Gap

The "legacy logic" on older A320s defaulted the aircraft's lateral mode to GA TRK (Go-Around Track) the moment the thrust levers were advanced to the TOGA detent. In simple terms, GA TRK means the aircraft stops navigating and simply continues flying the track it was on when the go-around was initiated.

This posed a significant danger, particularly during complex RNP-AR (Required Navigation Performance - Authorization Required) approaches. The development of this modification was largely driven by RNP-AR requirements to ensure the aircraft doesn't roll wings level while navigating a curved missed approach in a valley. With the legacy logic, the only way to follow a procedure's required turn was for a pilot to manually push the HDG/TRK knob on the Flight Control Unit (FCU) to arm NAV mode. Forgetting this single step could be catastrophic.

If you forget to push that HDG/TRK knob to arm NAV, you might just follow GA TRK straight into terrain.

The "NAV in Go-Around" modification solves this by automating that critical action. However, its behavior differs based on the type of approach being flown—a crucial distinction for a pilot’s mental model.

• Scenario A: Managed Non-Precision Approach (e.g., RNP-AR) When a go-around is initiated from an approach like FINAL APP, the NAV mode stays engaged. The aircraft never stops navigating laterally and will not interrupt a required turn. This provides seamless guidance through the most challenging missed approaches.
• Scenario B: ILS (Precision Approach) When a go-around is initiated from an ILS, GA TRK engages initially, but NAV is automatically armed (in blue on the Flight Mode Annunciator), provided a valid missed approach is in the flight plan. NAV will engage automatically once capture conditions are met, commanding the aircraft to follow the published procedure without the pilot needing to touch the FCU.

This automation reduces workload and mitigates a critical human-factors trap during one of the most demanding phases of flight.

2. The 'Gotcha' That Can Disable the Safety Net

Even smart automation has exceptions. A specific manual action by the pilot can inhibit this safety feature: the Heading Preset.

Consider a common ATC instruction on final approach: "In the event of a missed approach, fly runway heading." As a proficient pilot, you would preset that heading on the FCU. This direct, manual input is where the logic changes. If a heading is preset on the FCU, the automatic NAV engagement logic is inhibited.

Herein lies the trap that can catch even experienced crews: If you preset a heading in response to ATC, but then circumstances change and you decide to fly the published missed approach, the auto-NAV feature will not activate if you forget to clear the preset. The system sees the preset heading and assumes the pilot’s intention is to fly that manually selected heading, not the FMS flight plan.

This reveals a core philosophy of Airbus autoflight: a direct pilot input on the FCU is always interpreted as the most immediate and authoritative command, overriding pre-planned FMS guidance.

3. It's a Feature, Not a Universal Standard

The "NAV in Go-Around" logic is a modification dependent on specific FMGEC software standards; it is not present on all A320 aircraft. This creates a significant risk for pilots who fly a "mixed fleet," where they might move between an aircraft with this modern automation and an older one without it on the same day.

Relying on an automation feature that may not exist on your particular airframe is a recipe for error. This reality reinforces the most crucial takeaway for any A320 pilot operating in the modern environment: Never assume the automation is there—verify it on the FMA (Flight Mode Annunciator).

This practice is the fundamental discipline of maintaining mode awareness—knowing what the automation is doing, what it is about to do, and why. A glance at the FMA is the only way to confirm the aircraft’s guidance and ensure you are the final authority on its flight path.

Final Thoughts: Trust, But Verify

The "NAV in Go-Around" modification is a powerful safety enhancement. It directly protects against a known human-factors vulnerability, especially in complex RNP-AR environments where a missed approach demands immediate and precise navigation.

But this system is an exceptional safety net, and it is the pilot's understanding of its logic—including its designed inhibitions—that gives it true power. True expertise is not just knowing what the automation does, but understanding the conditions under which it will not do it. The system is designed to assist, not replace, a vigilant and knowledgeable pilot.

The next time you are in the simulator doing a Go-Around, take a split second to glance at column 2 and 3 of your FMA. Did NAV arm? Or are you drifting on a track?