Germania B737 near Malaga on Mar 3rd 2018, cabin pressure problems
Last Update: May 30, 2019 / 20:56:31 GMT/Zulu time
The airline reported that the aircraft lost cabin pressure for unknown reason, the aircraft diverted to Malaga.
On Mar 15th 2018 Spain's CIAIAC reported the flight crew anticipated turbulence and illuminted the fasten seat belt signs. Subsequently cabin crew felt rapid changes of cabin pressure, the cabin pressure rate indicators confirmed there was a problem with the cabin pressure with the cabin altitude increasing. Moments later the cabin altitude warning activated, the flight crew donned their oxygen masks. The pilot monitoring noticed that the "FLT ALT" and "LAND ALT" indicators showed dashes only and conluded that a double failure of the cabin pressure controllers had occurred. The passenger oxygen masks were automatically released when the cabin climbed through 14000 feet, the cabin altitude reaches 15,000 feet. The flight crew declared emergency and initiated an emergency descent. During the descent the crew was able to manually regain control of the cabin pressure after which they cancelled the emergency. The aircraft diverted to Malaga. There were no injuries and no damage as result of the incident, which is being investigated by the CIAIAC.
On Sep 19th 2018 Germany's BFU released their March 2018 bulletin reporting the occurrence was rated a serious incident, the BFU representing the state of operator has joined the investigation led by the CIAIAC. The aircraft lost cabin pressure, the crew initiated an emergency descent and diverted to the nearest suitable airport.
On May 30th 2019 Spain's CIAIAC released their final report concluding the probable causes of the incident were:
The investigation was unable to realiably determine the cause of this incident.
- According to the studies conducted during the investigation into this incident, it may have been caused by two possible faults.
Initially, the #2 cabin pressure controller (CPC2) commanded the outflow valve (OFV) to open completely. The upset that opened the OFV was caused by corrupted data in the CPC. The source of that corrupted data was either a SEU or the result of failing solder joints.
Later, due to the stiffness of the OFV, the #1 cabin pressure controller (CPC1) was unable to return it to its closed position and thus stabilize the cabin pressure. This may have been a factor contributing to the severity of the depressurization. It was possible to identify what caused the stiffness of the OFV.
- After the incident, suspecting that both cabin pressure controllers had failed simultaneously, they were replaced; however, various anomalies continued to occur involving the loss of cabin pressure.
- The aircraft operator did not provide information on what caused the loss of cabin pressure after the cabin pressure controllers were replaced. Moreover, it is not known if these subsequent incidents were analyzed in detail by the operator.
On 3 March 2018, before the incident, two other incidents involving cabin pressure were reported. It is thought that the lack of a detailed analysis of these prior incidents by the operator’s maintenance technicians could have been a contributing factor in this incident.
The CIAIAC described the sequence of events:
During the cruise phase, while at FL380, the cabin crew felt intense and sudden changes in pressure. After looking at the cabin rate of climb indicator, they realized there was a problem with the cabin pressurization. Seconds later, the visual and aural cabin altitude warning was activated, after which the crew donned their oxygen masks.
The pilot monitoring noticed that the flight altitude (FLT ALT) and landing altitude (LAND ALT) readings were displaying dashes, which led the crew to conclude that there must have been a dual failure of the cabin pressure controller (CPC). In the meantime, the cabin altitude had uncontrollably reached 15,000 ft. The passenger oxygen masks deployed automatically once the cabin altitude rose above 14,000 ft.
The crew declared an emergency situation (MAYDAY) to the air traffic control service in Casablanca, Morocco, reporting their intention to make an emergency descent. The ATS did not authorize the emergency descent and instead instructed the crew to contact Spanish ATS.
After contacting Spanish ATS, the crew reported they were making an emergency descent.
During the descent, the crew manually regained control of the cabin pressure, after which they decided to cancel the emergency declaration.
The crew decided to divert and land at the Málaga Airport, which they did without further incident.
Three passengers were minor jured as a result of the event.
The CIAIAC reported the outflow valve was analysed and faults were found with connecting cables, the pins and nuts were corroded, several bearings were worn and several weld points were cracked in the power supply.
Both safety relief valves were checked, one had a loose washer, the other failed the differential response pressure test.
Analysis of both cabin pressure controllers (CPC) concluded that one CPC had suffered a fault which caused the loss of cabin pressure, the other CPC suffered another independent fault which contributed to the severity of the depressurization.
The CIAIAC analysed:
As the operator is no longer operating, a safety recommendation will not be issued to the maintenance technicians to have them correctly use the information provided by the cabin pressure control system and the Fault Isolation Manual so as to properly identify and solve the problem.
Following this incident, the cabin pressure controllers were replaced and a loss of cabin pressure test was done as per the AMM 05-51-91-790-801 rev 64, after which the airplane was returned to service. However, various anomalies continued to occur:
- On 6 March 2018, an entry was made in the aircraft’s maintenance log involving “loss of cabin pressure. Replace cabin pressure control module”, after which the cabin pressure module selector was replaced.
- Subsequently, on 10 March 2018, both safety relief valves were replaced, as was the outflow valve. This change was prompted by a constant change in the cabin altitude climb/descent rate of between +400/500 ft/min and -400/500 ft/min during the cruise phase.
That is, despite the replacement, on 4 March, of the two cabin pressure controllers, problems were reported on 6 and 10 March. The operator did not provide information on what caused these new incidents. Moreover, it also did not indicate if more incidents involving loss of cabin pressure were reported after 10 March.
With respect to not authorizing the emergency descent the CIAIAC analysed:
When the incident began, the aircraft was in the CASABLANCA FIR. The crew, therefore, declared the emergency (MAYDAY) to the CASABLANCA air traffic control service in Morocco, reporting their intention to make an emergency descent. But the control service did not authorize the emergency descent, instead instructing the crew to contact Spanish air traffic control. ICAO Annex 11, Air traffic services, to the Convention on International Civil Aviation, includes a requirement on the services to provide to aircraft in the event of an emergency, which states:
“2.24.1 An aircraft known or believed to be in a state of emergency, including being subjected to unlawful interference, shall be given maximum consideration, assistance and priority over other aircraft as may be necessitated by the circumstances.”
No safety recommendation is issued to Moroccan air traffic control services since the ICAO already considers in its regulation, applicable to signatory States of the Convention on Civil Aviation, the requirement to provide consideration, assistance and priority over other aircraft to an aircraft that has declared an emergency.
This article is published under license from Avherald.com. © of text by Avherald.com.
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