Yan B734 near Kiev on Jun 23rd 2018, loss of cabin pressure
Last Update: September 19, 2019 / 16:34:18 GMT/Zulu time
Incident Facts
Date of incident
Jun 23, 2018
Classification
Incident
Cause
Loss of cabin pressure
Airline
Yanair
Flight number
YE-223
Departure
Kharkov, Ukraine
Destination
Batumi, Georgia
Aircraft Registration
UR-COI
Aircraft Type
Boeing 737-400
ICAO Type Designator
B734
Ukraine's NBAAI rated the occurrence a serious incident and opened an investigation.
On Sep 19th 2019 the NBAAI released their final report in Ukrainian only (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a Ukrainian only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe).
The report states the aircraft was dispatched with the right hand PRSOV (Pressure regulating and Shutoff Valve) inoperative. The aircraft was thus limited to a maximum of FL250.
The report concludes the probable causes of the serious incident were:
complete loss of compressed air supply to the air conditioning systems due to the automatic close of the left hand PRSOV, when the temperature of the incoming compressed air rose beyond 490 degrees F/254 degrees C due to clogging of the precooler of the left hand engine, while the PRSOV of the right hand engine was deactivated.
Related factors were:
- non-standard phraseology used during emergency radio communication in order to descend the aircraft
- insufficient training and qualification of technical personnel regarding elimination of defects in the aircraft pneumatic systems.
The NBAAI reported that following a flight on Jun 20th 2018 the crew had written up, that a big difference between left and right cabin pressure of up to 30PSI occurred and several "Bleed Trip Off" messages occurred. The crew did not state which controller showed higher pressure or which controller tripped off. A B2 maintenance engineer (instead of the B1 maintenance engineer needed for this type of issue) diagnosed the issue and disabled the right hand PRSOV in accordance with the minimum equipment list. The investigation did not find information about the troubleshooting session and why the engineer associated the fault with the right hand engine.
Several further events occurred during flights on Jun 21st and 22nd, however, it was impossible to make any reliable understanding of the Ukrainian text (with the assistance of translation software only) and identify maintenance activities and events with any degree of certainty.
The NBAAI analysed that the crew was aware of the right hand PRSOV being deactivated under minimum equipment list requirements resulting in the limitation to a maximum of FL250.
The NBAAI continued analysis, that during the climb through about 11000 feet the left hand bleed air tripped off, the crew stopped the climb, worked the related checklists and was able to restore the left hand bleed air supply. The aircraft continued the climb requesting FL240. ATC cleared the flight to climb to FL280, the crew denied FL280 stating their maximum FL was 240, ATC cleared the flight to climb to FL240. Climbing through FL160 the left bleed air tripped off again. The crew stopped the climb, worked the checklists and were able to restore the bleed air system again, and continued the climb now requesting and being cleared to FL200. After levelling off at FL200 the left hand bleed air tripped off again and could no longer be restored. The crew released the passenger oxygen masks manually and initiated a descent to FL100 - with ATC reporting the crew never requested nor was cleared to descend to FL100 and ATC claiming the aircraft attempted to divert to Kiev Zhulyani at FL200 again without communicating the diversion to Zhulyani. Ultimately ATC cleared the flight to divert to Zhulyani at FL200. The crew attempted several times to receive clearance to descent, without the use of the usual phrases, the controller did not understand the requests. The use of non-standard phrases suggests the crew was in a stressful condition and high emotional tension. Only about 8 minutes after the left PRSOV failed the last time the controller finally understood the crew request (now: "Descend, request descend flight level one zero zero") and cleared the flight to descend to FL100.
Incident Facts
Date of incident
Jun 23, 2018
Classification
Incident
Cause
Loss of cabin pressure
Airline
Yanair
Flight number
YE-223
Departure
Kharkov, Ukraine
Destination
Batumi, Georgia
Aircraft Registration
UR-COI
Aircraft Type
Boeing 737-400
ICAO Type Designator
B734
This article is published under license from Avherald.com. © of text by Avherald.com.
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