Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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8.3.4. Ground-Based Aircraft Emissions
Other reports in this collection
It is not within the scope of this report to consider all of the ground-based activities associated with aviation. Overall emissions resulting directly from aircraft flights do
include emissions associated with taxiing and the use of auxiliary power units at the gate. These emissions are considered briefly here.
8.3.4.1. Auxiliary Power Units
Auxiliary power units (APUs) are engine-driven generators contained in the aircraft (usually in the tail) that provide the aircraft with necessary energy during the time
the aircraft is at the gate. Part of the generated energy is used for air conditioning. As an alternative, the required energy can be supplied by ground-based equipment
that delivers electrical power at 400 Hz and preconditioned air to the aircraft. Herau (1992) investigated the financial and energy savings of such ground-based
installations at Brussels Zaventum Airport's 2000 terminal and concluded that a significant net saving of carbon emissions could be achieved. At Zurich Airport in 1997,
about 68,000 aircraft used terminal A and B, which has the facility to provide preconditioned air and 400 Hz power. Provision of these services achieved estimated
savings of about 95% in APU fuel consumption and emissions. However, fuel used by APUs is only a relatively small part of the total fuel use of an aircraft. For
example, for B737, B747, A310, MD81, and F100 aircraft, average APU fuel use is only 2.6, 0.8, 1.4, 2.5, and 3.5% of the fuel use at cruise per hour of operation,
respectively (USFAA, 1982, 1995). British Airways estimates that the amount of fuel used by an APU is less than 1% of the total fuel used by an aircraft.
8.3.4.2. Taxiing
Although standard landing and take-off (LTO) cycles have been used for simplicity, there are large variations in LTO cycles from airport to airport. Although landing and
take-off times are quite similar for similar fleet mixes, the amount of taxi/idle varies significantly from airport to airport (Wayson and Bowlby, 1988). This variance in taxi/
idle time is the key factor in the variability of emissions from aircraft during airport operations (USFAA, 1982, 1988). Various scenarios have been discussed and
attempted to reduce these emissions. These scenarios include the use of high-speed taxiways, towing of aircraft to runways (Fleuti, 1992), last-minute start-up,
improvements in engine design, restriction of certain aircraft types, realignment of taxiways, improvements at the gate area, and taxiing in with minimal engines
running.
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