Non-Engagement of the Go-Around Modes in CLEAN Flaps Configuration

An A319 aircraft was on descent with autopilot and autothrust ON. The flight crew was preparing to perform an ILS interception from above. The aircraft experienced moderate turbulence conditions during the approach phase. ① The aircraft captured the localizer 10 NM from the runway threshold (fig.1). The aircraft was descending in V/S mode at 2 000 ft/min in CLEAN flaps configuration, and with a selected altitude of 2 500 ft QNH. ② The aircraft intercepted the ILS 3° glide path from above at approximately 2 500 ft QNH, which was 7 NM from the runway threshold, at a speed of 225 kt.

③ Crossing 2 300 ft QNH, the aircraft speed was 236 kt increasing. The flight crew decided to extend the landing gear to reduce the speed.

④
Crossing 1 300 ft QNH, the aircraft was still in CLEAN flaps configuration and its speed was 240 kt. The flight crew pushed the thrust levers to TOGA to initiate a go-around. The LOC and G/S guidance modes remained engaged and the aircraft started to accelerate toward the ground, along the 3° glideslope.

⑤ Crossing 1 130 ft QNH, the aircraft speed was 243 kt increasing. The flight crew selected gear up, but the VLO for retraction of 220 kt was already exceeded.

⑥ At approximately 800 ft, the flight crew selected a 3 000 ft target altitude and pulled on the altitude knob-selector. The OP_CLB guidance mode engaged and sent a nose-up command to the autopilot. Aerodynamic forces meant that retraction of the landing gear was difficult. The nose landing gear retracted, but the left and right Main Landing Gear (MLG) remained extended.

⑦ The overspeed warning triggered due to the VLE (280 kt) exceedance. The PF disconnected the autopilot and applied nose-up inputs. The aircraft reached 312 kt at 600 ft before climbing back up to 3 000 ft where the PF reengaged the autopilot in ALT mode. The MLG fully retracted 2 min 30 s later while in level flight, with a speed of 205 kt at 3 000 ft. The flight crew eventually performed a second approach and safely landed the aircraft.

High-energy approach

The aircraft started its glideslope interception from above in CLEAN configuration at high speed. As a result, the flight crew was not able to sufficiently slow down the aircraft to stabilize its speed and they decided to perform a go-around.

Non-engagement of the go-around guidance modes

On A320 family, the SRS go-around mode and GA
_
TRK mode engages if:

• The flight crew sets a thrust lever at the TOGA detent, and
• The aircraft is airborne, or on ground for less than 30 s, and
• The slats or the flaps are extended.

Therefore, when the PF pushed the thrust levers to TOGA, the SRS and GA
_
TRK modes did not engage and the autopilot remained in G/S and LOC final approach modes.

Crew reaction time

It took 30 s for the crew to react and disconnect the autopilot, leading to an overspeed condition (312 kt with main gear extended) near the ground (600 ft).

At the time of publication of this article, on all Airbus aircraft except the A220 and the A350 with PRIM P12 and subsequent standards, the flaps configuration must be selected other than a CLEAN flaps configuration in order to activate the go-around guidance modes. Table 1 summarizes the slats/flaps condition for the activation of the go-around guidance modes applicable for each Airbus aircraft type. Full conditions for activation can be found in the FCOM description chapter for flight guidance on each aircraft type.

A220 and A350 aircraft with PRIM P12 and subsequent standards

A220 aircraft are not concerned by this non-engagement of the go-around modes in CLEAN flaps configuration: the VGA and GA modes are activated when the flight crew presses one of the TOGA switches on the thrust lever regardless of the position of the slats/flaps.

On A350 aircraft with PRIM computer standard P12 and subsequent standards, the go-around modes are also engaged in CLEAN flaps configuration if the aircraft is below the altitude selected on the FCU altitude and below 2 500 ft RA.

Flight crews must be aware of the potential for go-around guidance modes to not engage on some aircraft when the aircraft is in CLEAN flaps configuration.

The FCTM states that if the thrust levers are set to the TOGA detent during approach with the FLAPS lever at 0, the following occurs:

• The AP/FD remains engaged in approach or landing mode (e.g. G/S, LOC, LAND, FLARE on the FMA)
• The FMS does not engage the go-around phase and remains in APPR phase
• LVR CLB flashes on the FMA.

This means that when the thrust levers are set to the TOGA detent, the aircraft energy will rapidly increase, but the aircraft will remain on its approach path. In this situation, the flight crew must take appropriate action without delay.

Correct SOPs application should prevent the aircraft from being in a CLEAN configuration during final approach. The SOPs state that the aircraft should be at least in CONF 1 at the start of the final approach in the case of a decelerated approach, or in landing configuration in the case of an early stabilized approach.

Glideslope interception from above

When intercepting an ILS glideslope from above, the FCTM recommends that the flight crew should select at least CONF 2 to ensure that the aircraft speed does not increase during the interception.

Constant monitoring of the FMA as per SOPs enables a quick detection of the non-engagement of the go-around modes, allowing a quick flight crew reaction.

An update of the flight guidance mode was launched on A320 family, A330, and A380 aircraft to have a similar engagement logic as the A350 fleet fitted with the PRIM P12 or subsequent standards. The updated logic will enable the engagement of the SRS and GA TRK when in CLEAN flaps configuration, if the flight crew sets the thrust lever to TOGA and provided that the aircraft is below 2 500 ft AGL AND is below the FCU altitude (fig.3). The planned availability of the flight guidance modification of each aircraft type is indicated in Table 2.