Etihad A320 near Karachi on Mar 5th 2018, loss of cabin pressure

Last Update: May 3, 2019 / 18:03:29 GMT/Zulu time

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Incident Facts

Date of incident
Mar 5, 2018


Flight number

Aircraft Registration

Aircraft Type
Airbus A320

ICAO Type Designator

An Etihad Airbus A320-200, registration A6-EIF performing flight EY-200 from Abu Dhabi (United Arab Emirates) to Karachi (Pakistan) with 76 passengers and 6 crew, was descending through FL270 towards Karachi when the crew observed the cabin altitude climb through 8000 feet and increased their descent, the cabin altitude however continued to climb and reached 10,000 feet. The passenger oxygen masks deployed. The aircraft continued for a safe landing on Karachi's runway 25L about 30 minutes later.

The United Arab Emirates GCAA reported the aircraft received minor damage. The occurrence was rated a serious incident and is being investigated.

The occurrence aircraft had conducted a test flight EY-9104 from Abu Dhabi to Abu Dhabi just prior to departure for flight EY-200.

On May 3rd 2019 the GCAA released their final report concluding the probable causes of the incident were:

The Air Accident Investigation Sector determines that the cause of the Incident was the slow depressurization of the cabin during descent due to the number one cabin pressure controller (CPC1) processing corrupt landing field elevation data.

The corrupt value for the landing field elevation was, most probably, caused by a bit corruption in the memory cell of the digital electronic system of the CPC1, which led the flight crew to carry out an emergency descent and to manually deploy the passenger oxygen masks.

Contributing Factors to the Incident

The Air Accident Investigation Sector identifies the following contributing factors to the Incident:

- CPC1 as the system that was controlling the cabin pressure control system did not trigger an excessive cabin pressure warning while controlling the cabin towards higher altitude of the landing field elevation, with a cabin altitude rate of 300 to 400 feet per minute. However, the CPC2 triggered the excessive cabin altitude warning when the cabin altitude reached the warning threshold. The landing field elevation used by CPC2 was 96 feet, which was approximately the OPKC airport elevation.
- The corrupted memory was, most probably, caused either by a single event upset (SEU) in one memory cell of CPC1, or by erroneous data caused by fatigued solder joints on the ICs of the main board of the CPC1.

The GCAA detailed the sequence of events:

After takeoff and climb, the Aircraft cruised at FL370 and the flight proceeded normally.

At 1327:27, the Aircraft commenced its descent, and as it passed 28,300 feet pressure altitude, the flight crew noticed that the cabin altitude was increasing at a rate of about 300 feet per minute.

The flight crew decided to level off at FL270 in order to check if there was any improvement in the cabin altitude. However, no improvement was evident and the cabin altitude continued to increase. The Commander decided to continue the descent.

At 1335:11, the Commander decided to don the flight crew oxygen masks as the cabin pressure was increasing and had almost reached 9,000 feet. At this time, the Aircraft was descending, passing 25,700 feet.

The Commander then commenced an emergency descent by gradually increasing
the vertical speed as the Aircraft passed FL250. The Co-pilot informed Karachi area control center (ACC) that EY200 was performing an emergency descent due to cabin pressure failure, and he declared a PAN-PAN.

As the Aircraft passed through 19,200 feet pressure altitude at 1337:05, an excessive cabin pressure altitude (‘EXCESS CAB ALT’) warning triggered on the electronic centralized aircraft monitoring (ECAM). At this time, the Aircraft position was about 45 nautical miles west-south west of OPKC.

During the emergency descent, the cabin altitude rose above 10,000 feet, and as the Aircraft was passing approximately 16,400 feet pressure altitude the flight crew decided to deploy the passenger oxygen masks manually. After the deployment of the passenger oxygen masks, the Commander instructed the passengers to use the masks and the cabin crewmembers ensured that all passengers used the masks.

Once the Aircraft was below 10,000 feet pressure altitude, the flight crew removed their oxygen masks.

When the Aircraft was passing 9,580 feet pressure altitude at 1339:38, the Co-pilot informed the ACC controller that EY200 had completed the emergency descent, and he cancelled the PAN-PAN.

At 1340:37, the excessive cabin pressure altitude warning ceased. At this time, the Aircraft had reached 8,000 feet pressure altitude and maintained level at that altitude. The cabin manager was then called and requested by the Commander to check the condition of the passengers and she reported that all the passengers were fine. The Commander then briefed the cabin manager and he advised that the passengers could remove their oxygen masks.

The GCAA reported the aircraft had suffered eight additional occurrences with the cabin pressurization and cabin pressure controllers between Jan 16th and Mar 4th 2018.

Still in the factual section, point 1.16.4, the GCAA stated as root cause: "From the evidence stated above, the CPC in control (CPC1) performed correctly. The given indications inferred that CPC1 performed the ‘normal’ operations of cabin pressure control for a high elevation landing field. The cabin altitude rate of 300 to 400 feet per minute was well within the defined rate limits for the descent internal (DI) mode for high altitude operation. These limits were +250 to +750 feet per minute. As indicated by the data, CPC1 was in control and the cabin altitude rate and the outflow valve position were quite stable and appropriate for the controlled decompression rate. However, the landing field elevation of 96 feet did not fit the ‘normal’ value for a high elevation landing field. This means that although the landing field elevation was adjusted correctly, CPC1 did not use the correct value to regulate the cabin altitude towards the scheduled landing field elevation of 96 feet. CPC1 must have used a corrupt value, which led it to regulate the cabin altitude towards a high landing field. Therefore, it is likely that the root cause of this event was within the control mechanism of CPC1."

The investigation thus focussed on a corrupted memory mechanism causing the corruption of the landing pressure. The investigation however was not able to reproduce the fault. The consideration whether the investigation was dealing with a single event upset or a single event latch up as well as recognition that "Some cases of cabin pressurization events in the past were traced back to erroneous data caused by fatigue in soldered joints, due to aging effects." prompted the investigation to conclude that re-soldering RAM chips IC702 and IC703, used for calculating the scheduled landing pressure, could solve the issue.
Incident Facts

Date of incident
Mar 5, 2018


Flight number

Aircraft Registration

Aircraft Type
Airbus A320

ICAO Type Designator

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