MIAT B738 near Toulouse on Jun 8th 2016, loss of cabin pressure
Last Update: December 17, 2018 / 14:51:34 GMT/Zulu time
Incident Facts
Date of incident
Jun 8, 2016
Classification
Incident
Cause
Loss of cabin pressure
Airline
MIAT Mongolian Airlines
Flight number
QS-1160
Departure
Prague, Czech Republic
Destination
Seville, Spain
Aircraft Registration
EI-CSG
Aircraft Type
Boeing 737-800
ICAO Type Designator
B738
The occurrence aircraft remained on the ground for about 5 hours, then positioned back to Prague reaching FL340 enroute, but has not yet resumed service about 28 hours after landing in Toulouse.
On Nov 18th 2017 the US NTSB reported the NTSB had joined the investigation led by the Mongolian AIB as state of Manufacture and Design of the aircraft (editorial note: which usually means the investigation has been finished and the NTSB have received the final report).
The Mongolian Civil Aviation Authority (MCAA) released their final report in Mongolian dated Feb 24th 2017 (updated Aug 17th 2018) concluding the probable causes of the serious incident were:
The Boeing 737-800 registration EI-CSG needed to divert to Toulouse due to the reduced pressure in the cabin during the flight from Prague to Seville.
The main reason for the loss of pressure was that both cabin pressure controllers (CPC) failed again. During the flight Prague-Kos (Greece) earlier the day the crew had already dealt with the failure of both CPCs.
Contributing factors
the following factors may have contributed to insufficient tightness of the pressure vessel and reduced cabin pressure:
- two faults in the pressure vessel
- faults in both CPCs, poor reliability and performance of CPCs
- during the flight Prague-Kos earlier the day the cabin altitude had increased to 10,028 feet, no cabin altitude warning had activated.
- following the flight Prague-Kos maintenance analysis was incomplete and flawed
- the High Pressure Water Separation System (HPWS) mixer muff and HPWS condenser components were defective and the structure drain valve was not closed
The MCAA reported the crew received indication of a cabin pressure fault while climbing through FL110 out of Prague and switched the system to ALTN, after which the indication extinguished. When the aircraft was enroute at FL350 about 45nm from Toulouse the crew received the "AUTO FAIL" indication again. The crew switched the system to manual, however, the cabin pressure continued to decrease, the cabin altitude warning activated. The crew descended the aircraft according to the relevant checklists and diverted the aircraft to Toulouse.
The MCAA reported the aircraft had encountered automatic cabin pressure control failures earlier the day already during the flight from Prague to Kos. The crew had selected ALTN first, then proceeded to MAN control and continued the flight to Kos for a normal landing with manual cabin pressure control. The maintenance engineer, licensed to perform that task, checked the BITE fault code 14, then initiated a BITE test of CPC#2 which resulted in a OK indication.
Following the landing in Toulouse maintenance checked the BITE fault codes on both CPCs and found CPC#1 did not display anything as if the CPC was not powered. CPC#2 again showed fault code 14 (wiring issue). The circuit breaker for CPC#1 was pulled, the CPC#1 was re-racked, then the CPC#1 showed fault code 32. Following ground BITE tests both CPCs showed OK. The aircraft was released under minimum equipment list requirements to position back to Prague, however, encountered AUTO FAIL messages again during the positioning flight. Both CPCs, the HPWS mix muff and HPWS condensor components were replaced, the structure drain valve was found not closed and was replaced, too.
On Jun 10th 2016 the aircraft returned to service however again suffered problems with the #1 cabin pressure controller with cabin altitude climbing at up to 3000-4000 fpm during two flights, BITE tests following those flights showed OK. The CPC was again replaced, in addition the outflow valve assembly was replaced. The integrity of the CPC wiring and the connectors were tested.
Laboratory examination of the removed components confirmed all three removed CPCs were defective. The removed outflow valve was found working normally.
Some time in 2018 the Mongolian Aircraft Accident Investigation Bureau also released their English version of the final report dated Aug 17th 2018 (editorial note: the above summary is based on the Mongolian text dated Feb 24th 2017 as downloaded on Nov 18th 2017).
Incident Facts
Date of incident
Jun 8, 2016
Classification
Incident
Cause
Loss of cabin pressure
Airline
MIAT Mongolian Airlines
Flight number
QS-1160
Departure
Prague, Czech Republic
Destination
Seville, Spain
Aircraft Registration
EI-CSG
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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