Ground Speed Mini

Disclaimer: 

▪︎This content is Not an official document and does not represent the views of Airbus or any other aviation authority.

▪︎The information provided may be incorrect or misinterpreted and should not be relied upon for decision-making. 

▪︎Always refer to official documents and consult with a qualified aviation professional before making any decisions based on the information provided in this blog post.

▪︎The information provided in this blog post is based on personal study and review.

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Vapp close to Vmax 

The reported tower wind was 10kts of headwind, which was inserted into FMGC, but the headwind on the ND displays as 30kts of headwind, and the aircraft is quite heavy.

I was on final approach, and the Vapp speed was close to the Vmax flap speed of the final configuration due to the effect of Ground speed mini.

 

 If the actual headwind is much stronger than the tower inserted wind, especially when the aircraft is heavy (close to maximum landing weight), the target Vapp speed on final approach might be close to Vmax.

 

Due to the possibility of reaching Vmax during the approach, I selected speed, but the aircraft handling was quite difficult without managed speed and the help of ground speed mini.

Planning config full or config 3, there is a possibility that the Vapp speed added by ground speed mini might reach the Vmax of that configuration.

 

How can I continue the approach with managed speed without being getting close to Vmax speed? 

 

 

 

 

GROUND SPEED MINI FUNCTION

 

The FMS computes Vapp, taking into account the tower headwind component, as a minimum of VLS + 5 knots. 

The greater the headwind component, the higher the calculated Vapp (up to a maximum of 15 knots)

 

 

 

Based on this calculated Vapp speed, the Flight Guidance (FG) system computes a managed speed target, which is Vapp plus an additional increment. 

This increment varies by aircraft but is essentially the difference between the current headwind component and the manually inserted tower headwind component.

 

MANAGED speed target computation 

 

 

Airbus safety megazine #24 Control your speed during approach..

 

 

VLS + ∆     

 

Based on this calculation, the additional increment added by the Flight Guidance (FG) system can be incorporated into the table, whether it is added by FMS calculation due to the inserted tower wind or by the FG due to the current wind. We can focus on the extra speed added from the VLS.

 

In this table, we observe that with an actual headwind of 30kt, the managed speed target decreases when we input additional tower headwind components into the Flight Management System (FMS).

Therefore, The headwind component inputted into the Flight Management and Guidance Computer (FMGC) affects the target managed speed calculated by the Flight Guidance (FG) system.

 

 

Target managed speed changes to lower speed after inserting more headwind component into FMS

 

 

 

 

 Managed Speed Target Computation: A320 CEO vs. NEO

 

A320 NEO

- Managed Speed Target Computation

  - The Flight Guidance (FG) continuously computes the managed speed target, which is equal to VAPP plus an additional increment.

  - This increment accounts for one-third of the difference between the current headwind component and the tower headwind component.

 

 

 

A320 CEO

-Managed Speed Target Computation

  - The Flight Guidance (FG) continuously computes the managed speed target, which is equal to VAPP plus an additional increment.

  - This increment accounts for the difference between the current headwind component and the tower headwind component.

 

- The managed speed target has the following limits:

    - VAPP, as the minimum value.

    - VFE next, in configurations 0, 1, 2, 3, or VFE minus 5 knots in configuration FULL, as the maximum value.

 

 

 

 

Conclusion 

No matter what the current headwinds are, or even with tailwinds, the managed speed target airspeed will be calculated with VAPP as the minimum, which is VLS plus one-third of the FMGC-inserted tower headwind components.

This means that the more wind we input into the FMGC, one-third of these headwind components will be added to VLS to determine VAPP. This VAPP will be used to calculate the target approach speed, which is part of the ground speed mini function.

During final approach, if we insert less wind into the FMGC than the current headwind components, the managed speed target will increase, potentially up to VFE-5 kt, making it difficult to control in strong headwinds on final.

Although the managed target speed seems to increase with more wind input into the FMGC, during the final approach, if the current headwind is strong, it will actually reduce the targeted VAPP since the managed speed target is VAPP plus the difference between the current and tower headwind components.

When we insert more wind into the FMGC than is actually present, the VAPP is calculated higher than normal. This means that even with strong winds on final, the VAPP speed seems stabilized at the calculated VAPP. However, as the wind reduces near the ground, the managed target airspeed remains as VAPP plus one-third of the headwind components.