Russian carrier S7 Airlines has modified its de-icing procedures after a number of recent incidents involving Boeing 737-800s.

The Moscow-based airline states that crews have observed “changes in the operating parameters” of engines on the type, resulting in decisions to return to the parking bay for technical inspection.

“It was revealed that the unstable operation of the engine was caused by contamination of compressor blades, due to the ingestion of de-icing fluid particles,” says the carrier. S7 says this situation has a “cumulative” effect.

Federal air transport regulator Rosaviatsia says it held a meeting with S7 management, after three occurrences in the space of 10 days during January.

“Investigation into the aviation incidents continues,” it states, but adds that it made recommendations to the airline.

S7 737-800-c-Anna Zvereva Creative Commons

Source: Anna Zvereva/Creative Commons

S7 suggests the low-slung engines on 737-800s can ingest de-icing fluid from the apron

Boeing 737-800s are fitted with CFM International CFM56 engines, which hang close to the ground, and the airline believes fluid on the apron during de-icing can be sucked into the powerplant.

The airline stresses that the engines remained fully operational and were “not impaired” during the incidents, and the operating parameters did not exceed limits.

S7 says Moscow and other regions of Russia are experiencing “more difficult” winter weather conditions than normal.

“We are already seeing a record number of cases of aircraft de-icing,” it adds.

Given these circumstances, the airline is adapting its de-icing procedure for the 737-800, carrying out the process only with the engines turned off.

It has also reduced the intervals between engine washes and introduced additional borescope checks for contamination of the compressor blades.

“Flight safety is a key priority for S7 Airlines,” says the carrier, which operates around 20 passenger and cargo 737-800s.