Airframe, engine manufacturers, and airlines are investing billions of dollars into biofuel technology, hoping to derive a new formula of powering air travel into a cleaner future. However, as the proliferation of this fuel source continues, safety and reliability questions are coming into focus.

In recent months, Boeing, Air China, Honeywell, Gulfstream, Alaska Airlines, and others have all announced various biofuel initiatives. Starting on Wednesday, Alaska Airlines will fly 75 commercial passenger flights in the United States powered by a synthetic fuel made from used cooking oil. The $170 million joint venture between Tyson Foods and Syntroleum Corp. meets aviation and military safety, sustainability and performance standards.

Last week, an Air China-owned Boeing 747-700 flew a two-hour mainland flight from Beijing International Airport, which was fueled by more than 10 tons of biofuel, a 50-50 mixture of petroleum-derived jet fuel (Jet A-1) and fuel excogitated out of jatropha seeds, a Brazilian-based plant resistant of drought and pests containing about 27 to 40 percent oil.

This heightened interest in biofuels also prompts a series of safety and efficiency questions for companies and passengers alike. Are these experimental fuels safe? What are the affects of this new-age fuel on aircraft engines, performance, maintenance or reliability? Would you trust a soybean to bring you, for example, from New York to Hong Kong?

Last week's Air China flight was a result of a 2010 agreement between China's National Energy Administration and the U.S. Trade and Development Agency to develop requirements of Chinese biofuels. Honeywell UOP, PetroChina, Boeing and Air China were involved in the project.

Boeing, engine manufacturers, the U.S. Air Force, UOP Honeywell, the Defense Advanced Research Projects Agency along with others completed the research and testing necessary to prove synthetic paraffinic kerosenes as a drop-in replacement for petroleum jet fuel in 2009, according to Boeing. The research led to a new American Society Testing and Materials (ASTM) standard, D7566, which clears the way for agencies to begin approving biofuel for use in jets.

The fuel used in the Air China flight underwent the new Bio-SPK Biofuel Standard before the Beijing demonstration.

Any biofuel that is approved for use by commercial aviation, by definition, has been found to be essentially identical to petroleum-derived jet fuel, therefore biofuels are not expected to have antagonistic operational issues or differences, according to Nathan Brown, deputy executive director of the Commercial Aviation Alternative Fuels Initiative (CAAFI), a public-private partnership.

Jatropha oil operation showed that power output is almost the same for both diesel and plant oil operation in an August 2011 study conducted at the School of Engineering- University of Warwick, a public research university in Converty, U.K.

Published in the Journal of Scientific & Industrial Research, the study found that global energy demand is increasing due to population growth and individual consumption; energy demand is forecasted to be five times greater in less than 100 years. By using plant-based biofuels, energy will be conserved, efficiency would be greater and the amount of greenhouse gases (GHG) emissions would curtail.

Thermal efficiency of the oil used in the Air China flight for engine operation is 5 percent less than that of a fossil diesel, according to the study. When engines were deconstructed to see the affects jatropha oil had, there was a coke formation inside the engine cylinder, only in small deposits. Injectors were found reasonably clean, according to the study. No corrosion or erosion occurred in injectors.

The study demonstrates that trigenerations system, where heat of the byproduct (jatropha) is used for cooling off the engine, is possible using a variety of locally available non-edible pure plant oil, annihilating the contingency of foreign petroleum oil.

Nitrous oxide (NOx) emission is higher in jatropha oil when compared to NOx emission of fossil diesel. NOx is the fourth largest contributor to GHG, having more impact per unit weight than carbon dioxide.

The Environmental Protection Agency (EPA) proposed emissions standards for aircraft gas turbine engines in July 2011, which contains standards and related provisions previously adopted by the International Civil Aviation Organization (ICAO) the year prior. EPA proposed two new tiers of stringent emissions standards for oxides of NOx, according to the agency.

The Intergovernmental Panel on Climate Change (IPCC) and the Scientific Assessment Panel asked ICAO to prepare a comprehensive assessment, Special Report on Aviation and the Global Atmosphere, which was published in 1999. The report concluded that aircraft emit gases and particles that alter the atmospheric concentration of GHG, triggering the formation of condensation trails and may increase cloudiness--all of which contribute to climate change.

Aircraft are estimated to contribute about 3.5 percent of the total radiative forcing, which measures climate change, according to ICAO.

The Clean Air Act of 1970 is an approach that was made under the Nixon Administration to regulate air pollution.

Air pollution without doubt leads to health problems, including aggravation of respiratory and cardiovascular disease, decreased lung function, increased frequency and severity of respiratory problems, increased susceptibility to respiratory infections as well as effects on the nervous system, cancer and premature death, according the American Lung Association (ALA) Energy Policy Development in February 2011.

NOx, Carbon Monoxide (CO) and volatile organic compounds are produced mainly by transportation, according to the EPA. These three elements contribute roughly 40, 60, 30 percent, respectively. In 2008, U.S. and international major air carriers operated over 7,800 aircraft, which flew over eight billion revenue miles (824 million passenger miles), and carried over 35 billion ton-miles of freight, according to ALA.

Air transportation has been getting more efficient in the last two decades, decreasing the average energy intensity of major carriers by 37 percent in 2008 compared to figures in 1988. The improvement is attributed to more efficient operations and aircraft, despite increasing passenger loads.

Boeing has conducted biofuel tests by airlines and military operators since 2008. Jatropha research conducted by the Seattle, Wash., -based manufacturer and Yale University's School of Environmental Science disclosed the non-edible plant could deliver strong environmental and socioeconomic benefits.

The results from this study led Boeing to partner with Air China and PetroChina. Additionally the findings prompted the company to launch projects throughout Europe, the Middle East, India, Australia, Mexico, South America and the Northwest United States, according to Boeings latest environmental report.

FAA established a voluntary program to reduce airport ground emissions at commercial airports in air quality nonattainment and maintenance areas. Voluntary Airport Low Emission Program (VALE), is a program to help airports meet their imperative as required by the Clean Air Act and to meet National Ambient Air Quality Standards (NAAQS).

VALE in theory reduces the amount of regulation pollutants and harmful air emissions the industry generates. The program is sponsored with financial and regulatory incentives in low-emission technology investment.

"The FAA and the airport community recognize that controlling airport emissions and meeting Federal and State air quality requirements are essential to the continued growth and improvement of public aviation," the agency stated in the report.