Incident Overview
On June 12, 2017, an incident occurred involving a Boeing 738 (B738) aircraft at airport LFPG. The event was classified as an incident by the State Commission for Investigation of Aviation Accidents (PKBWL), with the investigation concluded on August 8, 2017. No fatalities or injuries were reported among the 26 individuals on board.
Operational Sequence
During a flight from Reina Sofia (GCTS) to Poznań (EPPO), the crew received a MASTER CAUTION warning indicating low pressure in Flight Controls Hydraulic System B. Following the execution of non-normal procedures, the crew observed a gradual loss of hydraulic fluid in System B, decreasing from 84% to 81% over approximately 30 minutes. The crew performed checklists related to potential landing issues due to hydraulic fluid loss.
During descent, after extending flaps, the STB RUDDER system activated automatically. Configuration for landing proceeded without mechanical issues. However, when instructed by Approach Control (APP) to contact Tower (TWR), the crew entered an incorrect frequency of 119.775 MHz instead of the correct 119.975 MHz. Consequently, the crew executed a landing while mistakenly believing they had received clearance from Air Traffic Control (ATC).
Investigation Findings
The investigation determined that the primary cause of the incident was crew error, specifically the execution of a landing without obtaining valid clearance from ATC. The State Commission did not issue specific safety recommendations, noting that the operator had already implemented internal corrective measures, including technical maintenance and crew briefing.