Swiss RJ1H near Zurich on Jun 3rd 2015, hydraulic problems
Last Update: July 8, 2016 / 16:47:57 GMT/Zulu time
The occurrence became known through notification by Swiss Sicherheitsuntersuchungstelle (SUST) of Mar 16th 2016 indicating the occurrence was rated a serious incident, an investigation has been opened.
On Jul 8th 2016 the SUST released their final factual report in German concluding the probable cause of the serious incident were:
The "HI TEMP" indication for the green hydraulic system was most likely caused by a defect in the related engine driven pump.
The "HI TEMP" indication for the yellow hydraulic system was most likely caused by the failure of the heat exchanger cooling fan.
The SUST reported, that shortly after reaching cruise FL310 the crew received an overheat indication for the green hydraulic system and in accordance with FCOM shut the green hydraulic system down. The crew declared PAN and decided to return to Zurich with runway 28 in use (winds from 280 at 9 knots). The crew requested runway 34, this was declined however as the approach sector for runway 34 had not been blocked and lot of VFR traffic was in the sector. ATC offered an approach to runway 16, this was declined by the crew reasoning they would need to land with around 10 knots of tail wind. The crew decided to accept runway 28.
While on downwind for runway 28 the crew also received an overheat indication for the yellow hydraulic system. In order to avoid an emergency situation the crew decided to keep the yellow system operating, lowered the gear using alternate gear extension and continued for a safe landing in visual meteorological conditions. Due to the nose wheel steering not being available the aircraft needed to be towed to the apron.
The SUST reported that preliminary inspection did not reveal any obvious cause that could have explained the two overheat indications, however, both hydraulic fluid reservoirs felt warmer than normal. When maintenance tested the hydraulic systems with engines running, it became obvious that the engine driven pump supplying the green hydraulic system produced a pressre of 3300psi instead of 3100psi and produced abnormally high noise. Further checks also revealed the heat exchanger cooling fan of the yellow hydraulic system was defective. The engine driven pump of the green and the cooling fan of the yellow hydraulic system were replaced, the hydraulic fluids were checked for contamination with none found.
Inspection by the manufacturer of the engine driven pump revealed the drive shaft was strongly deteriorated. The stator and electrical wiring of the fan were found in poor condition.
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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