New approaches to the old ways of applying de-icing and anti-icing fluids to aircraft on the ground could soon yield cost savings to airlines struggling with record high fuel prices. The action is part of a broader push within the industry to optimise or reinvent existing protective fluid practices in return for fuel, safety and environmental gains.
Early adopters of potentially game-changing technologies include Calgary-based WestJet Airlines, which has since 2003 been using an automated de-ice and anti-icing fluid holdover time determination tool built by Danish company D-Ice - holdover time is the length in minutes that the aircraft's wing and tail surfaces will shed contaminants before take-off.
Others are increasingly taking advantage of specialised trucks that dilute glycol-based de-icing fluids based on the ambient temperature, saving money while maintaining flight safety. Later this year, three Canadian airlines will test a new steam-based de-icing technology at the gate for defrosting operations at three Canadian airports.
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© Brian McNair |
Consultant Michael Chaput, manager of projects and business development for Montreal-based APS Aviation, which provides research services to regulators and manufacturers, says defrosting operations on the first flight of the day account for around one-third of all de-icing operations worldwide. Chaput says queue times for the traditional application of de-icing or anti-icing fluids to aircraft for defrosting at the growing number of airports with centralised de-icing facilities average 25-30min - time that can upset schedules and waste fuel.
Airlines typically use so-called Type 1 de-icing fluids, a mixture of glycol and water, to remove frost or ice from aircraft. If precipitation exceeding a certain intensity is expected to fall for taxi and take-off, pilots generally call for a second protective layer, a Type 4 anti-icing fluid, typically glycol mixed with thickening agents and chemicals, to provide continued ice protection. In either case, the fluids will have a specified holdover time. For safety reasons, the pilot must be confident the aircraft will be airborne before the holdover time expires, and ice can again stick to the airframe.
STANDARD PROCEDURE
Standard procedure for pilots upon pushback from the gate is to choose the type of protection based on a series of approved paper tables that consider temperature and precipitation type and intensity, gathered through hourly weather reports and view from the cockpit. The result of the relatively ad hoc process, which provides a fairly broad holdover time estimate, is less than uniform.
APS monitored 1,459 departures by a large variety of airlines at Montreal's Pierre Trudeau International airport in the 2004-5 and 2005-6 winter seasons, finding that 61% of flightcrews made the most optimal fluid selection. However, 27% of the time, crews decided to have the aircraft sprayed with the more expensive Type 4 fluid when Type 1 would have sufficed. Another 8% did not de-ice, which could be problematic if contamination is difficult to see. Possibly most problematic were the 4% of flights that departed after the holdover time limit of the fluid had expired.
Chaput, whose employer, APS, creates the look-up tables that pilots use, says the methodology used to obtain the holdover time data is substantiated by "hard scientific data", but that flightcrews can not extract proper data from the tables as the information is on paper, requiring interpretation and extrapolation, and methods of estimating the intensity of precipitation by visibility are "archaic", he says.
Although safety is paramount - even a thin layer of frost can drastically affect the aerodynamic characteristics of high-performance aircraft wings - cost and environmental issues with the petroleum-based de-icing and anti-icing fluids are increasingly driving airlines to look again at standard procedures.
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Later this year, Canada is likely to implement a pilot programme to test a tempered steam system built by Ontario-based Chinook. The system provides a combination of water vapour and hot air to the aircraft surfaces using the booms and special heads on modified de-icing trucks. "We're never going to replace Type 1 fluids in the two-step [Type 1 followed by Type 4] process, but we could do a sizeable amount at the gate," says Chaput.
After three years of testing on aircraft like the Airbus A320 and Embraer 170/190 regional jets, Transport Canada this winter is to introduce limited operations of the technology at three Canadian airports with three participating airlines. "I would think full-blown operation and limited commercialisation could take place in 2009 or 2010," says Chaput.
Tempered steam may also be a solution for de-icing engine inlets before engine start to remove ice on or behind fan blades, preventing damage to the blades during engine start. Chaput says airlines typically use heated air from ground power units for this since glycol-based fluids are unsafe for use with engines.
FLUID COSTS
Reducing the amount of glycol-based fluid used is becoming crucial as the cost of the fluid and its environmental impact increase. Peter Graversen, chief executive of D-Ice, says an aircraft requires 250-300 litres (65-80USgal) of Type 1 and/or Type 4 fluid at around $1 a litre for Type 1 and $5 a litre for Type 4. Chaput says prices are likely to be double this year due to the rising costs of fuel.
One way to cut costs is to optimise the concentration of glycol in Type 1 sprays. Chaput says Type 1 blending has historically been 50% glycol and 50% water. The actual needed concentration of glycol is a function of temperature, and can often be lowered. So-called proportional blending is more common in Canada, but is increasingly becoming available using special spray truck in the USA, he adds.
Another cost and environmental savings can come from smarter use of protection, especially Type 4 fluids. While airports and de-icing facilities generally have processes in place to catch Type 1 run-off and Type 4 overspray (as much as 50% of the fluid misses the aircraft), Type 4 fluids are designed to remain on the aircraft until power-up on the runway, making clean-up more difficult or impossible. The highest profile environmental issue with glycol-based fluids is the depletion of oxygen from waterways downstream of the run-off.
With its D-Ice system, WestJet pilots leaving the gate at Montreal and Toronto's Pearson International airport now receive via datalink in the cockpit a precise holdover time for Type 1 and Type 4 fluids, simplifying the decision process for what protection is needed based on the estimated time until take-off.
Certificated by Transport Canada, the D-Ice system at both airports uses a variety of off-the-shelf meteorological sensors plus a D-Ice-developed titanium turbine that collects the precipitation, providing holdover time updates every 10min. Weather reports used to estimate holdover time with paper tables are generally updated every 60min. Graversen says as many as four stations are needed to cover a large airport. He says the US Federal Aviation Administration and the European Aviation Safety Agency are interested in the technology, but issues to be resolved include the liability that airports must assume to become the provider of holdover time information to airlines, as is the case in Canada.
WestJet says its only complaint about the system is that it is not at more airports.
Source: Flight International
