Smartwings B738 near Kosice on May 29th 2017, loss of cabin pressure

Last Update: December 15, 2018 / 22:29:05 GMT/Zulu time

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Incident Facts

Date of incident
May 29, 2017

Classification
Incident

Cause
Loss of cabin pressure

Airline
Smartwings

Flight number
6H-734

Departure
Warsaw, Poland

Destination
Tel Aviv, Israel

Aircraft Registration
OK-TSF

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Smartwings Boeing 737-800 on behalf of Israir, registration OK-TSF performing flight 6H-734 from Warsaw (Poland) to Tel Aviv (Israel) with 99 passengers and 6 crew, was enroute at FL390 about 120nm northeast of Kosice (Slovakia) when the crew initiated an emergency descent due to the loss of cabin pressure, the passenger oxygen masks were deployed. The aircraft levelled off at FL100 and diverted to Kosice for a safe landing on runway 01 about 45 minutes after leaving FL390.

A replacement Boeing 737-800 registration OK-TVO positioned to Kosice and is estimated to reach Tel Aviv with a delay of about 6 hours.

On Jul 20th 2017 Czechia's UZPLN reported the cabin pressure experienced sudden changes multiple times prompting the crew to perform an emergency descent to FL100, the passenger oxygen masks were released. Maintenance determined that the pitot tubes were blocked by a mixture of dust and flowers and supplied from the vertical stabilizer. The pitot tubes were replaced and the system blown clean.

On Nov 13th 2018 Czechia's UZPLN released their final report in Czech 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 Czech 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 concludes:

The cause of the serious incident was reduced throughput through static and dynamic ports which together with defective cabin pressure systems produced the indications and fluctuations of Cabin Differential Pressure.

The UZPLN reported the aircraft was enroute at FL390 when the crew received a master caution and observed fluctuating cabin pressure between 8 and 1 psi at least 5 times. Both captain (36, ATPL, 3,761 hours total, 3,486 hours on type) and first officer (27, CPL, 1,117 hours total, 951 hours on type) became dizzy and felt breathing became impossible, both flight crew donned their oxygen masks, initiated an emergency descent and annnounced to the cabin "rapid descent". The purser informed the flight crew that the passenger oxygen masks had not been deployed, the flight crew thus released the oxygen masks manually. The crew was unable to execute the non-normal checklists due to the abnormal breathing conditions, the situation stabilized during the descent and the crew worked the related checklists later on. After levelling off at FL100 the crew cancelled the emergency and diverted to Kosice.

The UZPLN analysed that both flight and cabin crew carried out the relevant procedures in accordance with the checklists and manuals.

There were "impurities" in the static and dynamic ports of the pressure measurement system. The concealment of the probes would only be possible if the aircraft was not in flight. The probes were blocked by non-organic substances, sand and dust, as well as by organic substances like pollen of flowers, fluff and insects, the impurities were "baked" inside the system. In addition the engine #1's (CFM56, left engine) temperature sensor was found damage by overtemperature, the precooler valve of the left engine was replaced due to not passing the required tests, the "high stage valve" was replaced due to not passing the required tests as well as the cabin altitude and cabin differential pressure indicators were replaced.

Some time in December 2018 the UZPLN also released an English version of the report.