Preventing FSII Contamination with DEF

Fuel System Icing Inhibitor (FSII) contamination with Diesel Exhaust Fluid (DEF) is a very serious threat to the safety of flight. There have been at least four known incidents where FSII was mistaken for DEF, leading to inflight emergencies, including both partial and complete engine failures, nine emergency landings, and at least one aircraft deadstick landing – narrowly avoiding a tragic outcome.

These contamination events are 100% preventable with the proper training and procedures in place. NATA urges its members and all refueling operators that utilize FSII and DEF to to adopt OBP-36-Preventing FSII Contamination with DEF and any Other Product.

NATA also offers training on FSII Contamination Prevention through our Safety 1st Training Center.

For questions regarding FSII Contamination with DEF, please contact


OBP-36-Preventing FSII Contamination with DEF and any Other Product
EI Video: Control of FSII and DEF at Airports
NATA Safety 1st Alert
EI 1538 Handling of Fuel System Icing Inhibitor and Aviation Fuel Containing Fuel System Icing Inhibitor at Airports
NTSB Alert
Aircraft Diesel Exhaust Fluid Contamination Working Group Report & Recommendations
Safety Risk Management DEF Report - August 30, 2019
DEFKit - DEF in FSII Test Kit