Alliance E190 at Alice Springs on Aug 24th 2023, high rate of descent on approach as result of man and machine out of sync
Last Update: August 2, 2024 / 09:13:28 GMT/Zulu time
Incident Facts
Date of incident
Aug 24, 2023
Classification
Report
Airline
Alliance Airways
Flight number
QF-1960
Departure
Darwin, Australia
Destination
Alice Springs, Australia
Aircraft Registration
VH-UYN
Aircraft Type
Embraer ERJ-190
ICAO Type Designator
E190
Australia's ATSB released their final report concluding the probable causes of the incident were:
- After accepting an ATC request at short notice to conduct a straight-in approach, the flight crew unnecessarily configured the aircraft with high drag in flight level change to expedite the descent. As the aircraft pitched down to maintain airspeed, the pilot flying made an inadvertent mode selection in the automatic flight system that went undetected by the flight crew.
- Due possibly in part to their workload, the pilot flying did not identify that the aircraft was starting to automatically capture the selected altitude, and selected a higher altitude, which disarmed the altitude select mode. This resulted in the flight director resuming the high rate of descent close to terrain. These changes were not promptly identified by the pilot monitoring due in part to their focus to visually assessing the terrain clearance.
Key finding
- The air traffic controller on the job training instructor detected the unusual descent and immediately alerted the flight crew.
The ATSB analysed:
When ATC asked the flight crew if they could alter their flight path to conduct a straight-in approach (instead of overflying the airport), the aircraft was approximately 12 NM from the airport and passing 6,600 ft AMSL on descent. The crew accepted and, on request, were cleared to track as required to ALDIM, which was about 10 NM from the aircraft.
With the intention of crossing ALDIM between 3,600 and 4,000 ft, the crew elected to increase the rate of descent by extending slats, flaps and speedbrakes, and then selected flight level change mode (FLCH) in the flight management system to ensure the aircraft did not exceed the 210 kt speed requirement set by ATC.
When the aircraft was 5.4 NM from ALDIM and passing 4,692 ft AMSL (around 800 ft higher than the intended crossing altitude at ALDIM), the crew further increased their descent rate by extending the landing gear despite the aircraft having sufficient track miles remaining to comfortably intercept a normal descent profile.
As the aircraft was in FLCH, there were no automated thrust changes. Consequently, when the landing gear was extending and the aircraft entered a turn, the increase in drag was not offset by an increase in thrust. As a result, the aircraft pitched nose down to maintain the selected speed of 200 kt, which increased the rate of descent significantly.
Shortly thereafter, and possibly influenced by their workload, the PF inadvertently changed the selected vertical control mode to flight path angle (either by selecting FPA or deselecting FLCH). At this time, the captain’s attention was outside the cockpit, monitoring terrain clearance, and they did not detect the mode change.
As the aircraft continued to descend, the flight director entered altitude select mode to level off at 3,300 ft. The crew did not detect the mode change or that the aircraft was levelling off. Rather, in an attempt to arrest the rate of descent, the PF selected a higher altitude. In doing so, the altitude select mode was deselected, the flight director automatically reverted to FPA mode and selected the current flight path angle, which at that time was -13°. Subsequently, the PF momentarily overrode the autothrottle by manually increasing the thrust and then selected a higher altitude. The aircraft descended to 1,498 ft (AGL) during this period at a 2,973 ft/min rate of descent.
In response to the excessively high rate of descent, the flight crew turned off the autopilot and raised the nose, leaving autothrottle engaged and the selected speed unchanged. Given the aircraft’s speed was above the selected value, the autothrottle did not immediately increase thrust and the aircraft continued descending (to 1,381 ft AAL) until the speed decreased towards the selected speed. The crew then selected a lower speed and the autothrottle increased to climb power.
When the OJTI detected that the aircraft was not where they expected, they immediately instructed the trainee controller to make a terrain safety alert. However, in this case the crew had already taken action to correct the descent.
Aircraft Registration Data
Incident Facts
Date of incident
Aug 24, 2023
Classification
Report
Airline
Alliance Airways
Flight number
QF-1960
Departure
Darwin, Australia
Destination
Alice Springs, Australia
Aircraft Registration
VH-UYN
Aircraft Type
Embraer ERJ-190
ICAO Type Designator
E190
This article is published under license from Avherald.com. © of text by Avherald.com.
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