Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
a flight plan and the required amount of fuel, although the captain decides how much fuel is finally carried. The pilot may adjust the amount to be loaded in light of any
exceptional circumstances and his or her own interpretation of the risk of diversion or likelihood of weather changes down the route. The amount of excess fuel carried
for safety reasons is likely to be one to several thousand kg per flight.
Other factors that introduce additional weight are potable water and emergency equipment. Adjustment of the amount carried to the anticipated requirement, with a
contingency allowance, could accomplish some fuel savings. The extent to which emergency equipment is carried varies from airline to airline and the nature of the
flight. In addition, aircraft weight is increased by customer service considerations such as quality of seating, in-flight entertainment, and duty-free goods.
Although little quantitative data are available, such weight reduction could result in a potential fuel savings on the order of 1-2%. As described, only part of this potential
reduction can be achieved. Hence, the potential reduction of total fuel burn from weight reduction is probably less than 1%.
8.3.1.4. Other Operational Issues
During very rare emergency situations, it may be necessary to jettison fuel into the atmosphere to reduce the overall weight of an aircraft to a safe landing weight. The
potential effects of this (relatively small amount of) jettisoned fuel are not described here. Chapters 2, 3, and 6 discuss the possible effects of emitting unburned
aviation fuel into the atmosphere.
Emergencies requiring jettisoning of fuel are mainly mechanical in nature, such as serious engine malfunction, or airframe structural failure. Severe illness of passenger
(s) is also a major cause of emergency landings. Jettisoning of fuel is largely confined to larger aircraft flying long-haul routes. For these aircraft, the maximum landing
weight may be significantly lower than the maximum take-off weight (both specified through certification by the manufacturer). In the event of an emergency that
requires fuel to be jettisoned, airline instructions, as specified in aircraft operating manuals, and local operating procedures call for the aircraft to climb to a specified
altitude or to fly to designated fuel dumping areas away from centers of population. British Airways estimates that only a very small percentage (on the order of 0.01%)
of fuel used by the aviation industry each year is jettisoned. This estimate is subject to major uncertainty, particularly with reference to the former Soviet Union, and
does not take into account military operations.
Other potential fuel-reduction measures include reducing non-revenue flights and changing the loading distribution of passengers, cargo, and fuel to change the
aircraft's center of gravity. However, such measures are not expected to have a significant impact.
8.3.1.5. Tradeoff between Noise and Emissions
Apart from aircraft emissions, noise exposure around airports is also an environmental issue. The relationship between noise exposure and fuel efficiency sometimes
involves a tradeoff. For example, the Aircraft Noise Design Effects Study (ANDES) concluded that ".a general rule of thumb is that a 3-decibel noise reduction at flyover
(where the noise rewards are greatest) would, on average, increase fuel burn and hence emissions by some 5%." (ICCAIA, 1994). This figure applies to a new aircraft
design; to achieve this reduction in noise at the other measuring points (approach and sideline), a higher fuel burn penalty is involved. For the same result to be
achieved by modifying an existing design, the ANDES study concluded that the penalty would be greater.
One major area of potential impact is in retrofitting of engine equipment on older aircraft to conform with current aircraft noise standards. For example, it is possible to
convert older, more noisy "Chapter 2" aircraft to comply with the tighter "Chapter 3" noise standards that will be a requirement of all civil subsonic jet aircraft operating
at airports in the United States in 2000 and in Europe and some other countries by 2002. Such a change is not possible for all "Chapter 2" aircraft. However, where it is
possible, the increased weight of noise abatement equipment ("hushkits") can lead to an increase in fuel consumption of up to 5%. The fuel increase depends on the
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