While relatively low fuel costs in the recent past have significantly sustained airline profitability, the fact that oil prices have been on the rise for some time now is pushing fuel-saving initiatives higher up on airline management's agenda. Operational considerations that focus on fuel burn, while not compromising safety, have been known and implemented by airlines for quite some time. But engineering-driven solutions for saving fuel have been much less scrutinized, despite the fact that aircraft weight reduction and engine health monitoring can result in high levels of improvement in fuel efficiency, especially when coupled with initiatives involving flight operations.
Weight Reduction
Weight reductions are the most direct and measurable fuel efficiency initiatives. According to Marcel Martineau, a fuel management consultant, the penalty for carrying extra weight varies from 2 percent to 4 percent per flight hour depending on the flight length; the longer the flight, the greater the cost penalty.
Philippe Reichen, an airline engineering consultant, said, “In comparison with most operational initiatives, once the weight has been removed, the result is immediate and permanent as long as the weight is not reintroduced on the aircraft. Operational initiatives depend on training and [continued] participation of all individuals involved and are therefore more difficult to implement and to reproduce.”
Weight reduction initiatives should be started as soon as, or even before, the aircraft begins flying. “Once added, weight is difficult to remove once the aircraft starts operation. Calculating weight impact, before and during equipping an aircraft, pays out in fuel saving from the first moment of operation,” said Reichen.
Engine Health Monitoring
"Engine health monitoring can be used to calculate and monitor initiatives that affect fuel burn with individual engines,” said Reichen. In fact, engine deterioration contributes to 80 percent of the increased fuel burn over the life of an aircraft.
A good engine health monitoring program can assist an operator in ensuring that the engines meet the maximum required takeoff power and still have a reasonable exhaust gas temperature (EGT) margin. “Operating an engine close to its minimum margin will often result in a much higher cost when refurbishing the engine, as more parts will need scrapping. Ideally, the monitoring should start when the aircraft enters into service. It is a good way to ensure that the aircraft is meeting the original equipment manufacturer’s promised performance, especially while the aircraft is still under warranty,” said Martineau.
Engines start deteriorating as soon as they begin operating, and anything that helps slow the deterioration improves engine life and saves fuel. “Engine health monitoring can help to confirm that initiatives implemented reducing engine fuel burn are paying dividends," said Reichen. "As deterioration starts as soon as the engines are operated, fuel saving initiatives should be implemented as early as possible to maximize the effect.”
How To Implement
There are some best practices to implement aircraft weight reduction and engine health monitoring, but it should be noted that the two initiatives are distinct, even though they complement each other. “Unless an operator is careful, a medium-size aircraft (A320/B737) will increase in weight by 200 to 400 kilograms over time," said Martineau. "Dirt, unnecessary equipment, humidity in the wall insulation, galley equipment, leftover magazines and newspapers, extra water bottles, etcetera will contribute to this weight. There are even cases of operators that carry cases of water that are never used; not to mention full tanks of potable water when it is barely used."
All weight reduction initiatives should only be started once an accurate weight baseline has been established. Reichen advises that aircraft be weighed regularly while in service and all weight changes should be recorded and noted. “All weight additions should be calculated for their impact on fuel burn and the resulting cost. All relevant personnel should be aware of the cost impact due to weight addition,” he said. “When it comes to engine health monitoring, this should be performed using and following the engine OEM’s processes and calculation standards.”
Safety Considerations
When it comes to initiatives that improve the economic bottom line, such as fuel management initiatives, there are safety considerations and specific precautions for technical departments to observe. “As required by the safety management system [SMS] all changes should be evaluated for their potential impact on safety using the change-management process before changes are actually implemented. A hazard analysis on the changes triggered by the initiatives has to be performed and the potential safety risks, if any exist, need to be evaluated in order to mitigate their potential impact,” said Reichen.
Conversely, however, fuel saving initiatives can improve safety as they require extra attention to the operation through increased situational awareness. “Through careful engine health monitoring, it is possible to remove the engine before it runs out of EGT margin for both economic and safety reasons,” said Martineau.
Significant saving potential
Both aircraft weight reduction and engine health monitoring can reduce fuel consumption by 2 to 5 percent, especially when coupled with efficient operating procedures. “For example, the average flight time for an A320 or 737 is approximately 90 minutes. So the fuel burn is around four tonnes. A pilot who carefully applies all the recommended fuel saving techniques can easily save from 200 to 300 kilos per flight,” said Martineau.
“A relationship [between the weight reduced and fuel savings] can only be established if the total saving of all other initiatives is known. As a base approach, the relationship of payload to the dry operating weight plus the fuel weight defines the efficiency of the flight,” said Reichen. “If the fuel load is 1,000 kilograms higher than actually required, approximately 4 percent of this fuel load [40 kg] will be burned to carry this 1,000 kilograms. Additional loads will almost always cause more fuel burn.”
Engine health monitoring can be used to calculate the impact of fuel-saving initiatives. “An example of such an initiative would be the engine core compressor wash that could result in fuel saving by improving compressor efficiency, which in turn improves the engine health. Such improvements, depending on the engine-airframe installation and the core washing procedure, could improve fuel burn [for a certain time frame] by approximately 0.7 percent if both engines are washed,” concluded Reichen.