Neos B738 at Bristol on Jun 1st 2019, descended below safe height on approach and again on go around

Last Update: April 23, 2020 / 20:27:24 GMT/Zulu time

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Incident Facts

Date of incident
Jun 1, 2019

Classification
Report

Airline
Neos

Flight number
NO-830

Departure
Verona, Italy

Aircraft Registration
I-NEOT

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Neos Boeing 737-800, registration I-NEOT performing flight NO-830 from Verona (Italy) to Bristol,EN (UK) with 167 passengers and 6 crew, was descending towards Bristol for a RNAV (GNSS) approach to runway 27, approach told them they had 33nm to touchdown and offered a shorter routing of 23nm. The crew accepted the shorter routing. At that point the aircraft was at FL100 at 280 KIAS, the crew deployed speed brakes and increased the selected airspeed to 300 KIAS. When the aircraft descended through 4715 feet at 3000 fpm the airspeed increased to 303 KIAS. The aircraft was routed directly to waypoint ELROV 9.8nm before the threshold of runway 27, which was expected to be passed at 2500 feet or above and maximum 210 KIAS according to the approach procedure. The aircraft crossed ELROV at 271 KIAS and 3276 feet MSL. The crew attempted to engage the autopilot in VNAV, the mode however did not remain engaged and changed to LVL CHG. The target altitude in the MCP was set to 1000 feet, the approach minima. The aircraft descende along the approach path with thrust at idle and a speed significantly above the required speed, already below the glide path. When the aircraft descended towards 1000 feet the autopilot engaged in Altitude Acquire mode, the rate of descent began to decrease. The tower controller was engaged with a push back, his assistant became concerned about the altitude of I-NEOT and drew the attention of the tower controller to the flight, the controller instinctively instructed a go around because not seeing the aircraft in a position he would expect. The crew pressed TOGA, the autopilot disconnected as per design, the pilot flying commanded the flaps into go around position, the flight director commanded a pitch up and the pilot flying followed the flight director indications. The aircraft began to climb. However, the target altitude at the MCP was still set at 1000 feet rather than go around altitude of 3000 feet. The aircraft climbed to 1302 feet and began to descend again. The crew reset the target altitude to 3000 feet, which dropped the autopilot out of Altitude Acquire and into Vertical Speed maintaining the current vertical speed which was a descent. The pilot flying continued to follow the flight director for 32 seconds. When the aircraft reached 1047 feet MSL, 457 feet AGL, the crew realized the aircraft was not climbing and pitched up. At almost the same time tower recognized the aircraft was not climbing and repeated the instruction to climb to 3000 feet. The aircraft was vectored for another approach and landed on runway 27 without further incident about 15 minutes later.

The AAIB released their bulletin releasing following conclusion:

Flying a shortened routing led to a rushed and unstable approach which did not follow the correct vertical flightpath. This was observed by ATC who instructed the aircraft to go around. The crew found themselves performing a go-around unexpectedly but did not know why they had been required to do so. The go-around was conducted with a mis-set altitude on the MCP, and neither crew member noticed for a significant period that the aircraft was descending during the manoeuvre.

Crews should always be ready to perform a go-around because there can be many reasons why they might have to, either internal or external to the aircraft, such as on instruction from ATC.

The AAIB reported at the time of the incident approach control to Bristol was staffed by a trainee under supervision by an experienced controller. The ILS for runway 27 was not available due to works in progress, NOTAMs hat been issued informing the crew to expect the RNAV (GNSS) approach to runway 27.

The AAIB analysed:

The incident began when the crew accepted a shortened routing offered by Bristol Approach. This meant the aircraft was above FL100 with less than 25 nm to run to touchdown. Whilst the trainee controller clearly had good intentions in offering the crew the routing, a more experienced controller might not have considered it appropriate given the speed and height of I-NEOT. However, it is the responsibility of the crew to accept or decline any shortcut offered having assessed whether it is suitable. It remains the prerogative of the crew to ask for extra track miles to touchdown any time they consider the current distance to be too short.

As a result of the shorter routing, I-NEOT had too little distance to descend and reduce speed ready for the approach. The speed of the aircraft over ELROV was 61 kt above the procedure limiting speed. As a result, the crew were unable to make use of the VNAV mode of the AFDS and the approach was begun in LVL CHG. Descending down the approach in LVL CHG meant the crew were unable to reset to go-around altitude as directed in the operator’s procedures. Had they done so the aircraft would have climbed straight away because the autopilot was engaged.

I-NEOT did not meet the stable approach criteria laid out in the operator’s Operations Manual and, in these circumstances, the operator’s procedures required the crew to go around. However, the passing of the stable approach barrier went unmentioned by the crew and was followed shortly afterwards by ATC instructing them to go-around.

The instruction to I-NEOT to go-around was based on an instinctive reaction from the tower controller who considered that the aircraft was dangerously positioned in accordance with MATS Part 1. Whilst the crew were not expecting it and could not understand the reason for it, all crews must be prepared to perform a go-around at any time during an approach. In this event, the fact that the MCP altitude remained set at the approach minima rather than the missed approach altitude caused a significant deviation from a normal go-around with the aircraft descending, unnoticed by either crew member, for a significant period. The controller and the crew members realised almost simultaneously that there was a problem and the aircraft began to climb. During the initial go-around the aircraft descended below 500 ft agl.

The crew experienced a technical issue with VNAV after the go-around which meant they were unable to fly the second approach using this mode. However, this issue was not the cause of VNAV disconnecting at the start of the first approach. That was caused by the significant excess speed that the aircraft had at the start of the approach. Regardless of the reason for the disengagement, all crews should be aware that automatic modes will not always be operational and alternatives or reversions, should they be available, should be discussed before the approach begins.
Incident Facts

Date of incident
Jun 1, 2019

Classification
Report

Airline
Neos

Flight number
NO-830

Departure
Verona, Italy

Aircraft Registration
I-NEOT

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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