SriLankan A333 near Learmonth on Mar 21st 2021, autopilot disconnected, altitude deviation

Last Update: November 1, 2022 / 14:33:44 GMT/Zulu time

Bookmark this article
Incident Facts

Date of incident
Mar 21, 2021

Classification
Incident

Flight number
UL-606

Aircraft Registration
4R-ALR

Aircraft Type
Airbus A330-300

ICAO Type Designator
A333

A SriLankan Airlines Airbus A330-300, registration 4R-ALR performing flight UL-606 from Colombo (Sri Lanka) to Sydney,NS (Australia) with 9 (nine) passengers and 7 crew, was enroute at FL390 about 500nm east of Learmonth,WA (Australia) when autopilot #1 disconnected. The aircraft climbed about 725 feet before the crew manually returned the aircraft onto FL390. The aircraft continued to Sydney for a safe landing without further incident about 3.5 hours later.

The aircraft departed for the return flight about 2 hours after landing.

Sri Lanka's AIB rated the occurrence an incident and opened an investigation.

On Nov 1st 2022 Sri Lanka's AIB released their final report concluding the probable causes of the incident were:

- The disconnection of the AP on both occasions was caused by a force applied to the F/O’s side stick. A warning was triggered as this was not the recommended procedure to disconnect the AP.

- Poor situational awareness and non-adherence to SOPs in handing over and taking over of controls culminated in the AP disconnection on two occasions and which resulted in loss of altitude.

The AIB summarized the sequence of events:

The first segment was operated by the Captain and the Cruise Pilot. The second segment where the subject incident occurred was operated by the Cruise Pilot and the First Officer. The third segment was operated by the Captain and the Cruise Pilot.

After approximately 3 hrs, the operating crew of the first segment had changed seats for rest purposes. For the second segment of the fight, the F/O (Cruise pilot) took over the left seat as the PM, while the relieving F/O seated on the right hand seat and acted as the PF. The PIC had gone to the cabin to take his rest.

At FL 390, at about 0310 UTC, the aircraft had experienced Autopilot disconnections followed by an altitude loss of about 1540ft at a rate of descent of 5700ft/min over Jakarta FIR.

The flight crew had not reported this incident to the Flight Safety Section of the Airline. The incident was detected by the Flight Safety Section during the routing FDA monitoring. Subsequently MORs were filed by the operating Flight Crew, and submitted to the CAASL through the Airline on 2nd April 2021.

In more detail the AIB described the autopilot disconnects:

The aircraft was in cruise at FL390. Auto Pilot 2 and both FDs were engaged in ALT CRZ/NAV mode. Auto Thrust was in active mode and Mach was managed at M 0.81. At about 03:10 UTC, AP 2 had disconnected with the master warning sounding. The aircraft, started to descend below the selected FCU altitude. A few seconds later AP 1 was engaged by the CP from the left seat. The aircraft was still in a descent. Subsequently, AP 1 also disengaged and the master warning wastriggered. Few seconds later AP 2 engaged by the F/O (PF). The aircraft lost altitude and descended approx. 1540ft at a rate of 5700ft/min on the VSI (Vertical Speed Indicator). Then AP2 was re-engaged by the cruise pilot in open climb mode and the aircraft commenced climb to FL 390.
Incident Facts

Date of incident
Mar 21, 2021

Classification
Incident

Flight number
UL-606

Aircraft Registration
4R-ALR

Aircraft Type
Airbus A330-300

ICAO Type Designator
A333

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

You can read 2 more free articles without a subscription.

Subscribe now and continue reading without any limits!

Are you a subscriber? Login
Subscribe

Read unlimited articles and receive our daily update briefing. Gain better insights into what is happening in commercial aviation safety.

Send tip

Support AeroInside by sending a small tip amount.

Related articles

Newest articles

Subscribe today

Are you researching aviation incidents? Get access to AeroInside Insights, unlimited read access and receive the daily newsletter.

Pick your plan and subscribe

Partner

Blockaviation logo

A new way to document and demonstrate airworthiness compliance and aircraft value. Find out more.

ELITE Logo

ELITE Simulation Solutions is a leading global provider of Flight Simulation Training Devices, IFR training software as well as flight controls and related services. Find out more.

SafetyScan Pro

SafetyScan Pro provides streamlined access to thousands of aviation accident reports. Tailored for your safety management efforts. Book your demo today

AeroInside Blog
Popular aircraft
Airbus A320
Boeing 737-800
Boeing 737-800 MAX
Popular airlines
American Airlines
United
Delta
Air Canada
Lufthansa
British Airways