With winter approaching fast, there will be changes in how airlines and airports run their operations in the Northern Hemisphere. The main difference will be the deicing of aircraft before departure, ensuring that crucial flight control surfaces are free from ice that could impact their performance. At the same time, engine performance is also affected during cold weather operations, including, surprisingly, some improvements when the temperature outside is less comfortable for those who walk the earth on their two feet.
1Stringent pre-flight checks
To ensure optimal performance of the aircraft’s engines, they must be checked before departure for any ice buildup
Much like with an aircraft’s control surfaces, engines are also susceptible to ice buildup on the nacelles and in the core. According to SKYbrary, a project initiated by EUROCONTROL, ice contamination of an engine can happen before or even during a flight. If ice is spotted during a pre-flight check, it must be removed from the nacelles. The site pointed out that “blowing snow, precipitation, freezing fog, slush, and other ground contaminants or airport snow removal operations can all result in the contamination of jet engine intakes and components.” As such, it must be removed.
However, the situation is more complicated because, unlike the fluids used to de-ice control surfaces, “engines cannot be de-iced with glycol-based fluids” due to potential contamination of the bleed air system. Usually, any loose ice is removed with a brush or a broom, while any ice within the engine should be melted with external heat sources, such as a Herman Nelson unit. Another option is to accelerate the engine to a specific engine fan speed (N1) for a brief period.
2More thrust is delivered to the engines
Since colder air is denser, the engines perform better, allowing pilots to use less runway during takeoff
During cold air operations, the outside air is denser since air molecules move slower. As a result, more air molecules enter an aircraft’s engine, requiring less fuel to maintain a proper air-fuel ratio. As a result, runway takeoff distances are shorter when the temperature is colder. According to a document by the United Nations Conference on Trade and Development (UNCTAD), the runway length requirements for a Boeing 737-800 during a standard day (15 °C, 59 °F) is 2,377 meters (7,800 feet). At 30 °C (86 °F), the runway length requirements increase to 2,469 m (8,100 ft), going up to 3,078 m (10,100 ft) at 40 °C (104 °F).
Notably, denser air also means that the wings can generate more lift compared to operations at high and hot airports, where the atmosphere is sparser, contributing to the shortened runway length requirements. According to a EUROCONTROL paper, “thrust and lift are proportional to air density, which is determined by the atmospheric pressure, OAT [outside air temperature – ed. note], and humidity at the considered elevation.”
3Affecting engine performance is affected when anti-ice systems are used
De-icing an engine or wing slats with its anti-ice system also negatively affects its performance since it requires more bleed air
Aircraft have onboard anti-icing systems that direct bleed air from the engines to wing surfaces and engine intake areas to prevent ice formation. According to a study by several Egyptian scholars, while the “anti-icing system in aircraft applications is considered a very important system to avoid the accumulation of ice especially on wing surfaces aircraft and engine intake,” it has a “drawback effect in the engine performance parameters according to the amount of bleed air extracted.” The study’s conclusion continued that increased bleed air ratio decreased the propulsive, thermal, and overall efficiencies.
However, some aircraft, like the Boeing 787, have increased fuel efficiency by using the bleed air system only to de-ice the engine. According to the manufacturer, “bleed air is only used for engine cowl ice protection and pressurization of hydraulic reservoirs.”
“The electrified functions are wing deicing protection, engine starting, driving the high-capacity hydraulic pumps, and powering the cabin environmental control system.”
As a result, eliminating a pneumatic bleed system “results in a more efficient engine operation due to reduced overall airplane level power requirements,” which, in turn, requires less fuel when the Boeing 787 is cruising. “The corresponding predicted improvement in fuel consumption, at cruise conditions, is in the range of 1 to 2 percent,” Boeing noted.
4Increased risk of damage
With ice buildup, there is an increased risk of the aircraft’s engine being damaged by the buildup
SKYbrary pointed out at least three engine-related damage risks regarding icy conditions. For one, the fan blades could be damaged if frozen deposits or ice are not removed before starting the engine. Secondly, an excessive ice buildup at low thrust settings could damage the engine’s blade tips when applying a higher thrust setting. In the worst-case scenario, even the engine core could ingest ice, potentially resulting in “partial loss of thrust or even flameout,” which, in turn, would result in an incident.
In 2004, a MyTravel Airways Airbus A320, registered as G-CRPH, was departing Harstad/Narvik Airport (EVE), Norway, when it veered off the runway during icy conditions. According to the final incident report by the Norwegian Safety Investigation Authority (NSIA) noted that while damage was limited “to a punctured left nose wheel tire, a separated and deformed left nose wheel hubcap and a broken nose leg taxi light,” the incident was caused by asymmetrical thrust from “by icing on the fan blades during the taxiing and holding before take off.”
5Worsening lubrication performance
While aircraft use special oil and other lubricants, they are not immune to extreme temperatures
According to the United States (US) Army’s Preventative Maintenance Magazine, “as the mercury dips, oil gets thicker and grease gels.” The magazine also advised that maintenance technicians should never fill an aircraft to the brim when servicing a plane in a cold environment. Oil will expand when it heats up, leading to potential leaks within the systems.
At the same time, the Aircraft Owners and Pilots Association (AOPA) pointed out that modern oils used in today’s general aviation (GA) engines “flow extremely well even at 0 °F (-18 degrees C),” the danger is that different metals within engines expand and contract. The latter is true when it is cold outside, meaning that there is a risk of parts not meeting the manufacturer’s minimal clearance specifications, which could result in a significant maintenance bill.
Source: simpleflying.com