Covering form of preliminary or final report

Date of event : 2017-05-29
Incident number :
Report : Final report
Place of event : In the area of Kyiv and Bratislava FIR
Registration mark : Serious incident
Weight category MTOM: : >5700 kg
Type of operation : Commercial and Air Transport
Plane / SFM : Airplanes
Type of plane / SFM : Boing B737-800
Health effects of event : Without injury
PDF document : pdf


On 30 May 2017, the operator informed the Air Accidents Investigation Institute of a serious incident of the B737- 800 aircraft, reg. mark OK-TSF, which occurred in Kyiv UIR and Bratislava FIR.

During a commercial flight from EPBC to LLBG at FL390 when flying in KYIV UIR, cockpit air over-pressure suddenly changed several times. The crew completed an emergency descent to FL100 and informed ATC. They interrupted flight on the planned route and landed at LZKZ without further complications. There were no crew or passenger injuries.

A check at LZKZ detected organic and inorganic pollutants in sensors and static/dynamic pressure piping. The following defects were then identified:
- Temperature sensor of engine No. 1 (damage caused by high temperature).
- Precooler control valve of engine No. 1 (failed to meet test check requirements).
- High stage valve of engine No. 2 (failed to meet test check requirements).
- Cabin altitude and differential pressure indicator oscillated between 8 and 1 psi at least five times.

The serious incident was caused by the reduced passability of the static/dynamic pressure system which together with the defects on aircraft pressure system components initiated the indication and fluctuating in indication of “Cabin Differential Pressure”.