Russian federal air transport regulator Rosaviatsia is urging aviation organisations to pay closer attention to the risk of aircraft fuel system contamination, after assessing a number of incidents over the past two years.

Rosaviatsia states in a June bulletin that the presence of contaminants – such as resin, impurities or micro-organisms – has a “detrimental effect” on the functioning of the fuel system, causing blockage of filters and other serious issues.

It cites two separate incidents involving Red Wings Yakovlev Superjet 100s, the first of which occurred during the take-off run from Istanbul on 25 April last year.

As the aircraft reached 142kt, a clogged filter alarm for the right-hand PowerJet SaM146 engine was activated, followed by a corresponding alarm for the left-hand engine after the jet lifted off. The crew of the twinjet (RA-89156) opted to return to the airport and conducted an overweight landing.

Examination of fuel samples revealed various impurities, some with an unusually-high sulphur content, possibly from fuel which came into contact with low-quality rubber within the ground-refuelling system. Other impurities included particles similar to paint chips, and phosphorus compounds used in hydraulic fluids.

Each of the identified contaminants “could have led to blocking of the fuel filters of both engines”, Rosaviatsia says.

It says a similar incident took place six months later, on 17 October, when filter alarms on both engines of another Superjet 100 (RA-89138) were sequentially triggered during initial climb.

Fuel samples revealed a “significant amount” of cotton and cellulose fibres. Inspection of the filters showed some elements had gaps in their epoxy resin joints.

Rosaviatsia also lists a Ural Airlines Airbus A320 incident, less than a week earlier, during which the left-hand CFM International CFM56 engine’s speed declined after take-off on 12 October. The crew shut down the powerplant and returned to the airport.

Analysis of the fuel-flow regulation system found organic deposits from heavy hydrocarbons which had passed through the filters.

The bulletin refers to organic contamination of an Antonov An-24RV which activated fuel-filter alarms for both engines during the take-off roll on 5 July 2023, prompting the crew to abort at nearly 100kt.

Rosaviatsia also highlights incidents affecting helicopters.

Its bulletin stresses the need to “analyse constantly and evaluate potentially dangerous factors” when providing aviation fuel supply services, tightening control over fuel quality, and carrying out unscheduled inspections of filter elements in refuelling facilities.