“Can you explain the Approach Ban philosophy?” or “when can you conduct a Discontinued approach?” are interview questions I have faced multiple times. It is important to have a clear understanding for when you can, and cannot continue an approach and what options you have for the missed approach.
Commencement of the Approach
Before commencing an approach to land, the Commander shall be satisfied that, according to the information available, the weather at the aerodrome and the condition of the runway intended to be used should not prevent a safe approach, landing or missed approach, with regard to performance information. If this is not the case, the advice would be to position the aircraft to take up a hold until a diversion plan is made or weather conditions improve.
- The Commander may commence an instrument approach regardless of the reported RVR/VIS.
- If the reported RVR/VIS is less than the applicable minimum, the approach shall not be continued:
- Below 1000ft AAL, or
- Into the final approach segment in the case where the DA/H or MDA/H is more than 1000ft AAL
- If, after passing 1000ft AAL, the reported RVR/VIS falls below the applicable minimum, the approach may be continued to DA/H or MDA/H.
- The approach may be continued below DA/H or MDA/H and the landing may be completed provided that the required visual reference is established at DA/H or MDA/H and is maintained.
The decision-making at 1000 ft AAL, whether or not to continue the approach, is referred to as the Approach Ban.
This is designed to give flight crew the opportunity to commence approaches where conditions are marginal but there is still a reasonable probability of a successful outcome. However, if the probability of a successful outcome was low, for example, if weather significantly below minimums, this may not be advisable. It also gives a clear and objective decision point for where the approach can be continued if visibility permits or where a missed approach must be executed if not.
Point 3. allows the pilots to continue the approach down to DA/H or MDA/H with RVR/VIS below minimums after passing the Approach Ban point. The reason being that of workload management combined with the fact the RVR/VIS is clearly dynamic and very close to the minimum required. It gives the crew the opportunity to fly to DA/H or MDA/H to assess the visual reference achieved. However, it should be noted that clearly the probability of a missed approach is increased in this scenario.
Missed Approach Techniques
Commencing an approach with Visibility close to minimums will naturally increase the probability of having to execute a missed approach. Here there are two different strategies that could be used:
- Go-around Procedure
- Discontinued Approach
- Go-Around Procedure
This involves advancing the thrust levers/throttles to TOGA position and ordinarily retracting some flaps and raising the landing gear. This can be a fairly aggressive maneuver as it is designed to quickly recover the flight path away from terrain by maximising climb performance.
- Discontinued Approach
The discontinued approach is an alternative technique to the go around procedure. In essence, it is a controlled interruption of an approach. It can only be performed when the aircraft is above the altitude selected on the FCU/MCP/Glareshield. Contrary to the go around procedure, the discontinued approach technique does not require the flight crew to set the thrust levers/throttles to the TOGA position. It would ordinarily come with a different SOP call, on Airbus, the PF must announce “Cancel Approach”. PF would then disarm any approach mode, causing the Autopilot/Flight Director system to return to basic modes such as heading and vertical speed.
The PF would then select appropriate modes to achieve the desired flight path. This is a much smoother and less dramatic manoeuvre but comes with limitations and considerations to execute it successfully. This manoeuvre cannot be used below 1000ft AAL (link to Approach Ban) and a full Go-Around Procedure must be executed.
As mentioned, it can only be performed when the aircraft is above the altitude selected on the FCU/MCP/Glareshield. This acts as a safety barrier as the Autopilot/Flight Director System would capture this altitude rather than allowing the aircraft to continue its descent once the approach mode has been disarmed.
Furthermore, the flight management system may also require updating with a relevant to-waypoint and destination. This is because TOGA has not been used and therefore the FMS remains in approach mode, rather than go-around mode. Therefore, it did not automatically sequence another approach.
In conclusion, it is important to have a clear understanding of the Approach Ban and its application on marginal weather days.
If you are initiating a Missed Approach while the aircraft is above the altitude selected, you may have a choice whether to fly the Go-around Procedure or the Discontinued Approach. With the aircraft below the selected altitude or below 1000ft AAL, there is no choice and it is mandated to execute the Go-around Procedure.
In both scenarios, an appreciation of the requirements and handling differences is important to ensure a well-handled manoeuvre. Briefing is key and having discussed the techniques in advance, you are far more likely to successfully execute the maneuver. The Discontinued Approach is generally less practiced and it is therefore advantageous to practice one in the simulator from time to time to keep the techniques current.