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| Date: | Wednesday 8 June 2016 |
| Time: | 18:35 UTC |
| Type: |  Boeing 737-8AS (WL) |
| Owner/operator: | MIAT Mongolian Airlines, opf Travel Service |
| Registration: | EI-CSG |
| MSN: | 29922/571 |
| Year of manufacture: | 2000 |
| Engine model: | CFMI CFM56-7B |
| Fatalities: | Fatalities: 0 / Occupants: 194 |
| Other fatalities: | 0 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | Near Toulouse -
 France
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Praha-Václav Havel Airport (PRG/LKPR) |
| Sevilla Airport (SVQ/LEZL) | |
| Investigating agency: | AAIB Mongolia |
| Confidence Rating: |  Information is only available from news, social media or unofficial sources |
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.
Accident investigation:
 |
|
Sources:
https://aaib.gov.mn/uploads/aac0f5fbc84fecea01b7c5d4af74b704.pdf
https://www.jetphotos.com/photo/8326459 (Photo)
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 07-Mar-2025 15:31 | Justanormalperson | Added |
| 07-Mar-2025 15:31 | ASN | Updated [Operator, Accident report, ] |
Corrections or additions? ... Edit this accident description
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