What happened
On February 12, 2006, an Air France Airbus A320-200, registration F-GKXJ, was performing flight AF1983 from Prague-Ruzyně (LKPR) to Paris Roissy-Charles de Gaulle (LFPG). Shortly after departing from runway 24, at an altitude of approximately 1,500 ft, the crew noticed a significant discrepancy in engine performance. The N1 speed of the left engine was at 80%, while the right engine (engine No. 2) had dropped to 66%.
This reduction in power occurred without any prior warning from the Electronic Centralised Aircraft Monitoring (ECAM) system. The pilot attempted to restore power by moving the thrust levers to the TOGA (Takeoff/Go-Around) position, but the right engine'N1 speed only reached 71%. Following these unsuccessful attempts, the commander declared an urgency and requested an immediate return to Prague-Ruzyně, along with the presence of airport emergency services. The aircraft landed safely at 15:29 local time. There were no injuries among the 7 crew members or 140 passengers.
The investigation
The ÚZPLN investigation focused on determining why the engine power dropped without warning and why the thrust levers failed to restore the required N1 speed. Technical inspections of engine No. 2 were conducted on the ground by the operator's maintenance personnel. The investigation examined the engine's maintenance history, noting that recent work in the vicinity of the engine sensors had been performed, including the removal of the starter.
Findings
Technical analysis revealed that the PS3 sensor hose had been worn through due to physical contact with the starter air supply pipe. The investigation established that the hose was positioned in a way that allowed it to touch the air supply piping during operation. This contact caused a leak in the hose, which was difficult to detect visually. The investigation concluded that the insufficient clearance between the PS3 sensor hose and the air supply pipe during installation was the primary cause of the failure.
Safety action
Following the incident, the operator performed inspections on several other aircraft equipped with CFM56 engines to check for similar wear on PS3 sensor hoses. It is recommended that aviation authorities verify that maintenance procedures for CFM56-B4 engines include adequate checks to ensure no contact exists between the PS3 sensor hose and the starter air supply piping.