Flying a Go-Around Managing Energy

Between 2010 and 2012, Airbus per-formed a survey on go-arounds that required a close examination of the approach phase of nearly 500,000 flights. The confidential survey gathered data from 12 airlines from all areas around the world. Amongst many facts that were established was the general go-around rate which was one go-around in 340 approaches for the A320 family fleet and one go-around in 240 approaches for the A330/A340 fleet.

The main outcome of this survey was that, above 1,200 ft AAL, over half of the go-arounds were performed without selecting the thrust levers to the TOGA detent (fig.1).

Perhaps the most obvious result of this research was that with go-arounds at heights above 1,200 ft the adherence to the Airbus standard go-around procedure was only about 50%.

The reason is that crews are reluctant to use TOGA power, even briefly, if they only have a short climb to their FCU Altitude.

In addition to the figure above, several other discreet areas of go-around management were analysed. These included configuration management, speed control, pitch control and the use of automation versus manual flight.

To initiate a go-around, Airbus has al-ways recommended the application of the standard go-around procedure with the selection of TOGA detent. With an air-craft that is flown according to the SOP there is no particular difficulty with such a procedure. But if the pitch target is not achieved and a go-around with maximum thrust is applied to a light weight aircraft, this may give rise to an excess energy situation. So the questions being asked were: is there a solution to limit the excess aircraft energy, and is there an alternative to the standard go-around procedure for these “high altitude” go-arounds?

(fig.1) Airbus survey on the use of TOGA during go-around 

To initiate a go-around, flight crews set the thrust levers to the TOGA detent. The engine thrust then increases to the maximum available thrust. Setting the thrust levers to the TOGA detent is important because the lever movement to TOGA engages the correct FMA modes and then, the FMS sequences the Missed Approach guidance that is pre-coded in the FMS Navigation Database.

However, in some cases, maximum thrust is often not required to perform a safe go-around and at some airfields the Missed Approach Altitude is quite low.

The SOP already mentioned that after having set the thrust levers to TOGA detent, if TOGA thrust was not required, the flight crew might retard the thrust levers as required. However, there was no additional recommendation for the flight crew on which position the thrust levers had to be set. 

Airbus now specifies in the procedure:

If TOGA thrust is not required, the flight crew should set the thrust levers to the CL detent, after having selected them to TOGA position just at the go-around initiation point.

This action aims at limiting the aircraft energy during the go-around phase.

Some operators have developed their own customized go-around procedures. These procedures have resulted in unexpected aircraft trajectory and energy situations. Therefore, Airbus developed a technique, based on the knowledge of all associated aircraft systems, to achieve the objective of performing a go-around without applying TOGA thrust. The technique, called “Discontinued Approach”, enables the flight crew to abort an approach without setting the thrust levers to the TOGA detent.

The main actions that flight crew have to perform are:

• De-selection of the approach mode
• Management of aircraft trajectory
• Selection of a new destination in the FMS, if required.

(fig.2) Depending on the altitude selected on the FCU, the flight crew may discontinue the approach.

The FCU altitude during a descent and approach is normally reduced in steps, with ATC clearance, until the initial approach altitude (typically 3,000 ft) is reached. At glide slope capture (G/S) or final approach commencement (FINAL APP) the FCU altitude is set to the missed approach altitude.

The flight crew uses this selected FCU altitude for the decision-making:

• At or above the FCU selected altitude: use either the go-around SOP for the Discontinued Approach Technique (fig.2)
• When below the FCU selected altitude: use the go-around SOP.

If the flight crew wants to apply the discontinued approach technique, they must go through the five following steps:

1. Call “CANCEL APPROACH”

2. Leave the thrust levers in the CL detent

3. De-selects APPR mode(s)

To de-select the approach modes, the flight crew can use the applicable pushbutton: APPR or LOC (if a LOC only approach is being executed). In the case of an ILS approach, for example, both these actions disarm or disengage the LOC and G/S approach modes on the FMA. This action ensures that possible spurious LOC and/or G/S capture (fig.3) are avoided. 

(fig.3) Spurious LOC and/or G/S capture

4. Manage the aircraft trajectory in vertical and lateral axis.

• Depending on the ATC orders, select a heading (HDG), or re-engage NAV if the intention is to fly the missed approach in the FMS Flight Plan (F-PLN).
• Select the appropriate vertical mode to descend or to level-off according to the altitude assigned by the ATC.
• Select a new speed according to the situation.

5. Enter a new DEST in the FMS, if required (fig.4)

If the flight crew intends to fly the missed approach and overflies the last waypoint of the approach, the FMS considers that the “destination” in the F-PLN has been achieved. The flight crew will have to enter a new destination, which could be the same airport or a diversion airport.

(fig.4) The missed approach remains available when disconti-nuing the approach. However, the FMS may have “lost” the destination