AD 2020-14-09 GEnx-1B Model Turbofan Engines Experienced Temporary Thrust Anomalies

The FAA is adopting a new airworthiness directive (AD) for certain The Boeing Company Model 737-8 and 737-9 (737 MAX) airplanes.

This AD requires removing Kathon FP 1.5 biocide from the fuel tanks and engines, installing a fuel limitation placard, and revising the existing airplane flight manual (AFM) to prohibit operation of the airplane with Kathon FP 1.5 biocide in a fuel tank or engine. This AD was prompted by a report indicating that Kathon FP 1.5 biocide added to fuel and running through the engines can lead to significant engine anomalies. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective July 15, 2020.

Supplementary Information: The FAA has received a report indicating that a Boeing Model 787 airplane equipped with General Electric Company (GE) GEnx-1B model turbofan engines experienced temporary thrust anomalies on both engines during descent into Kansai, Japan, on March 29, 2019. Specifically, both engines briefly fell below idle thrust, and the flightcrew received failure messages for both engines.

The FAA's review of the data from this incident indicated the thrust anomalies resulted from fuel control instability. The fuel tanks of the event airplane had recently been treated with Kathon FP 1.5 biocide for suspected microbial growth contamination. Salt crystals can form in the fuel under certain conditions after Kathon FP 1.5 biocide is applied. These salt crystals have the potential to cause slow response of engine hydromechanical control features, resulting in compressor stalls or flameouts, potentially on both engines.

Having similar fuel system architecture as the GE GEnx engines, the CFM International S.A. (CFM) LEAP-1B model turbofan engines, which are installed on 737 MAX airplanes, are also considered susceptible to a multi-engine loss-of-thrust-control event. This condition, if not addressed, could result in malfunction of the engine's control system hydromechanical unit due to undispersed Kathon FP 1.5 biocide contaminating and restricting the movement of internal parts. Because the fuel systems for both engines on an affected airplane are likely to be similarly affected, there is the potential for loss of thrust control on both engines. Loss of thrust control on both engines could result in failure to climb on takeoff, a forced off-airport landing, or an unacceptably high flightcrew workload.

However, after this biocide is added to the fuel tanks, adding fuel without biocide diminishes the hazard. Eventually, after the tanks have been refilled a sufficient number of times with untreated fuel, enough of the treated fuel is gone that the unsafe condition has been removed. Specifically, Boeing determined that operating the airplane, or any individual engine, for at least 30 flight cycles, while adding only fuel that has not been treated with this biocide, would flush the biocide from the fuel tank system and the engines. The FAA finds this number of flight cycles to be sufficiently conservative, and therefore has incorporated it the requirements of this AD.
The FAA's analysis of the risks posed by this issue has been ongoing, as has the information available to the agency. On March 10, 2020, the manufacturer of Kathon FP 1.5 withdrew that product from the aviation market, effective immediately. A copy of that letter is in the docket for this rulemaking. On March 25, 2020, the FAA issued a Special Airworthiness Information Bulletin (SAIB), which is in the docket for this rulemaking, regarding the effects of Kathon FP 1.5 and another biocide. Most recently, on June 25, 2020, the Japan Transport Safety Board issued an “Aircraft Serious Incident Investigation Report” regarding the March 29, 2019 incident. That report is in the docket for this rulemaking.

The FAA may consider similar rulemaking to address the unsafe condition on other airplane models, such as the aforementioned Boeing 787, pending findings from further investigation of other engines.

FMI: www.regulations.gov