Aircraft need power when on the ground – and increasing amounts of it, given the technical sophistication of today’s aircraft. Chris Lewis reports
Aircraft’s need today for more power while on the ground comes down to developments such as the increases in aircraft size over the years, not to mention the greater demand for passenger comforts such as air-conditioning and increasingly elaborate on-board electrical systems.
There is also pressure on airlines and airports to make their operations as ‘green’ as possible by minimising unnecessary emissions, as well as noise.
There are traditionally three ways in which these power requirements have been satisfied. First, aircraft systems can run off an aircraft’s own auxiliary power unit (APU). While this may be the case at the smaller and more basic airports, excessive use of APUs is increasingly being avoided on both environmental and noise grounds; many airports now ban unnecessary APU use for noise abatement reasons and instead encourage airlines to use portable ground power units (GPUs) or, where available, fixed electrical power.
ITW GSE describes APUs as “one of the great sinners, when it comes to both environmental and noise emission in the airports”, and airports often have strict rules about APU use, only allowing them to be turned on for a few minutes after aircraft arrival or before departure. Some, such as Hong Kong and a number in Spain, have imposed mandatory bans on turning on aircraft APUs except immediately before departure.
Mobile GPUs are the first alternative to APUs. These provide DC and/or AC power to keep an aircraft powered up on the ground while its engines are switched off, as well as to start the machine’s engines and APU. They are most usually diesel-powered, but can be run off batteries.
The second alternative to GPUs is fixed (installed), solid-state electrical power. This drastically reduces noise and emissions, which can have a significant impact on local air quality. Large-scale generators of electricity are more efficient at producing energy, and if they use water or wind power they can potentially produce no CO2 or other emissions at all.
Fixed electrical power systems feed electricity to an aircraft straight from the local grid – though it is typically converted to 115V at 400Hz – and it is also possible to use pre-conditioned air (PCA) from the airport’s own air system as an alternative to powering air-conditioning from an APU.
The power itself can be delivered either via an aircraft bridge through cable reel devices that can be wound out and wound back as required, or by systems buried in the concrete of the airport apron. ‘Pop-up’ pit systems are increasingly use,d which are simpler to use and ease access to more remote stands.
Fixed power can be as environmentally friendly as the local electricity supply allows, and airports and airlines have also been paying increasing attention to emissions from diesel, portable GPUs, where they are used. While GPUs are only one of many pieces of GSE found at airports, they do have high numbers of operating hours per year. The engines themselves have to meet the relevant standards, which are revised regularly.
GPUs and fixed ground power are both much cheaper to run than APUs in terms of fuel burned and maintenance costs. APUs form part of the aircraft system and as such, need maintenance at set intervals and also have much higher fuel costs than the alternatives.
ITW says that quite apart from the APU restrictions imposed by many airports, using solid-state power units and installed PCA units not only cuts carbon dioxide emissions by as much as 85%, it also reduces noise levels and the consequent cost-savings in terms of fuel and APU maintenance can be worth perhaps as much as 100,000 euros (US$117,000) per year per gate.
So, as Airports Council International (ACI) says, it is hardly a surprise that an increasing number of airports are either examining or actually installing this option, “as it brings both environmental and cost benefits”.
Already, at the larger airports ‘plug-in’ fixed electrical power (FEP) is routinely provided, with portable units mainly used in a back-up role or to provide some operational flexibility.
ITW GSE, which supplies GPUs, PCA systems and accessories to the aviation industry, says that wherever electrical power is available, “solid-state units are the obvious choice. They are environmentally friendly as they pollute less and are much more silent than diesel GPUs and they do not release any exhaust fumes. Another big advantage is their good operating economy that originates from high efficiency.”
Furthermore, solid-state units require less maintenance as they don’t have the moving parts subject to wear and tear and (normally) take up much less space than their diesel, mobile counterparts.
A diesel unit, however, operates without the need for electrical supply, says ITW, adding: “We still see a need for such units – on remote stands and for military use where (electrical) power is not at hand. But from year to year, we observe an increasing demand for green, solid-state power solutions.”
ACI agrees that diesel GPUs are still favoured in many circumstances because they are more mobile than electric GPUs, and appreciates that the benefits of even a diesel GPU are still considerable versus an aircraft APU. The airport trade body adds that there are also portable GPUs that are either run off electric converters or battery-powered, “which are not as efficient but are a valuable step along the way”.
Portable units are nowadays used mostly at less busy airports where the capital cost of fixed power is nt justifiable or where the flexibility required to handle aircraft of many different types and sizes is not compatible with whatever FEP is provided. They might also be used at remote stands, where it is not feasible or cost-effective to provide fixed power.
Demand for power units of all types is strong, says ITW, adding: “All in all, we have delivered more than 80,000 pieces of equipment to customers worldwide and believe that we are the only manufacturer that has such a track record.”
For example, ITW GSE has been awarded the contract to deliver both 400Hz GPUs and PCA equipment to Istanbul New Airport – the largest single contract in the history of the company.
ITW’s perception is that mobile solid-state units are now taking the lead in the industry. They are highly flexible, can be moved to other parts of the airport and even to another airport. In Scandinavia, for example, electrical supply is often available throughout the airport and frequently even on remote stands, so it is possible to power the aircraft using solid-state GPUs.
William Vasey – senior manager aircraft turnaround at Dubai-headquartered handling company dnata (part of the Emirates Group), says that fixed electrical power and installed preconditioned air are in favour at most airports. “As they are static and mostly underground, they don’t occupy the turnaround space, resulting in less congestion on the bay. Also, they produce no fumes or noise pollution or heat from running engines.”
Most modern aircraft power requirements are very sensitive, so more use is being made of power factor correction (PFC) technology. For example, the B787 Dreamliner’s electrical power requirement is very sensitive and requires three stand-alone and independent 90 KVA supplies. The aircraft will not accept the external power if there is any fluctuation in output from the GPU/FEP supply.
ITW adds that more or less all solid-state manufacturers use some kind of PFC technology to reduce ‘harmonic feedback’ into the mains supply as far as possible. This is important for other users of the same supply, as equipment may not function correctly if the mains supply is too ‘polluted’.
There is now some official encouragement around the world to support a switch to ‘greener’ forms of ground power. For example, in the US, the Federal Aviation Authority (FAA) has its Voluntary Airport Low Emission (VALE) programme, which Dallas/Fort Worth (DFW) – among other airports – has used to install new gate electrification systems for aircraft.
DFW has installed gate electrification and PCA at all 165 gates to prevent aircraft using APU systems for power and air while idling. According to the airport, “this successful initiative reduces ozone precursor (oxides of nitrogen and volatile organic compounds) and carbon emissions (while reducing airline fuel costs)”.
The extent to which schemes like VALE can be taken up does depend on how much control airports have over their airline customers’ activities in this regard. For example, one major beneficiary of the scheme, Port Columbus, had in the past allowed airlines to choose how they received their power supplies, with the result that some relied on the airport but others brought in their own equipment or used their own internal aircraft systems. It was only after deciding to take ownership of all jetways that Columbus was fully able to take advantage of the VALE scheme.
VALE was a product of former president Obama’s Climate Action Plan, and the relatively new incumbent of the White House may not be so generous towards such carbon-cutting schemes. The FAA has funded 92 VALE projects at 46 airports, since 2005, a total investment of $251 million in clean airport technology (a figure that takes in $196 million in federal grants and $55 million in local airport matching funds).
The programme covers more than ground power systems and has included, variously, electric-powered ground support equipment schemes, electric buses and even a solar-powered water-heating system for Boise Airport, Idaho.
Nevertheless, green ground power and PCA systems accounted for the majority of recent grants made, including: $2.4 million to purchase and install 11 GPUs and 11 PCAs for passenger gates at Memphis International Airport in Tennessee; five PCA systems for passenger gates and 68 electrical ground support recharging ports worth $1.5 million at George Bush Intercontinental Airport in Houston, Texas; $3.1 million to purchase and install 23 GPUs, five PCA systems and two air-chilling units for passenger gates at Dallas/Fort Worth International Airport, also in Texas; nine GPUs (and associated electrical infrastructure for remote parking sites) at Los Angeles International Airport, California, worth $4 million; $5.7 million to purchase and install 27 PCAs at passenger gates at Portland International Airport, Oregon; and $10.6 million to purchase and install five GPUs and five PCA system and associated infrastructure at five remote maintenance stations at San Francisco International Airport, California.
ITW also points out that states such as California and Texas have agreements with major airlines to reduce emissions from all their ground support equipment, which can include converting gasoline and diesel equipment to electricity and alternative fuels