Katerina Swanson
Auxiliary Power Units (APUs) are used on aircraft to provide electrical power on the ground to ensure turnaround operations, and can also be used in flight or during taxi in specific situations. The APU burn rate depends on the aircraft type, with Boeing 737 APUs consuming 110 kg/hour, A320 APUs burning 126 kg/hour, and B737-800 APUs burning 225 lbs/hour. Most APUs burn 200-250 lbs per hour under full load, which equates to 31-39 gallons per hour. This means that cooling an airplane during a 1-hour turn can cost between $32.55 and $93.60. Truckers have reported that their APUs use between 0.1 and 0.5 gallons per hour, depending on power and cooling load, with some claiming their units use less than half a gallon per hour.
| Characteristics | Values |
|---|---|
| APU burn rate per hour | 200-250 lbs (31-39 gallons) |
| Boeing 737-800 APU burn rate per hour | 225 lbs (102 kg) |
| A320 APU burn rate per hour | 126 kg |
| Ground Power Units (GPU) fuel usage per hour | <20 kg |
| APU fuel usage per hour for cooling in summer | 0.2-0.5 gallons |
| APU fuel usage per hour in extreme heat | 0.5 gallons |
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What You'll Learn
APU burn rate varies by aircraft type
The APU burn rate varies depending on the aircraft type. For example, the Boeing B737-800 has an APU burn rate of 225 lbs (102 kg) per hour, whereas the A320 has a higher burn rate of 126 kg/hour. The burn rate also depends on the power and cooling load. For instance, during extreme heat, the APU will use more fuel to maintain a cool temperature.
In general, most APUs burn 200-250 lbs per hour under a full load, which equates to 31-39 gallons per hour. This burn rate can be used to estimate the additional fuel needed for aircraft that will be idling their APUs for a certain period of time. For example, if a B737-800 is expected to idle its APU for 45 minutes to an hour, an additional 200 lbs of fuel should be added. If the aircraft is only idling for a quick turn, or less than 30 minutes, then 100 lbs of additional fuel is sufficient.
It is important to note that the APU burn rate is separate from the fuel burn of the aircraft's main engines. The APU provides electrical power on the ground to ensure turnaround operations, and it can also be used in specific situations during the flight or taxi, such as engine failure. By monitoring the usage and fuel consumption of the APU on the ground, airlines can identify opportunities to save fuel and reduce maintenance costs by using alternative power sources such as Ground Power Units (GPUs) and Air Conditioning Units (ACUs).
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Fuel burn impacts airline costs
Fuel costs are one of the largest and most variable expenses for airlines, accounting for 15-20% of total expenses. In 2019, U.S. airlines spent $3 billion on fuel in July alone, with overall airline fuel consumption remarkably stable despite increasing numbers of passengers and freight transported.
Fuel burn rates vary depending on the aircraft type, with most Auxiliary Power Units (APUs) burning 200-250 lbs per hour under a full load, or 31-39 gallons per hour. This means that cooling an airplane during a one-hour turn costs between $32.55 and $93.60, based on Delta's average jet fuel prices over the last five years.
Fuel efficiency in aircraft can be improved through better aerodynamics, weight reduction, and enhanced engine brake-specific fuel consumption. For instance, the Airbus A350 and Boeing 787 Dreamliner utilize lightweight composite materials in their designs, improving fuel efficiency. Additionally, turboprop airliners are more fuel-efficient than jet airliners due to their propellers.
Reducing fuel consumption is a critical goal for the aviation industry, as it leads to significant cost savings, financial stability, and environmental benefits. Airlines can achieve this through various means, such as improving system predictability, optimizing airspeed and altitudes, and reducing discretionary fuel loading.
By reducing fuel burn, airlines can lower their operating costs, which can lead to more affordable ticket prices for passengers. Fluctuations in fuel prices can also impact an airline's financial planning and stability, highlighting the importance of minimizing fuel consumption to mitigate these risks.
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GPUs and ground air cost money
The use of Ground Power Units (GPUs) and ground air comes at a cost. While pilots may be reluctant to turn on the Auxiliary Power Unit (APU) early due to the associated fuel costs, it is important to consider the costs of alternative power sources as well. GPUs can be differentiated into mobile and stationary units, with the former being more commonly used due to its ability to withstand challenging airport conditions while providing optimal power output at lower operating and maintenance costs.
Mobile GPUs typically consist of diesel power generators or large electrical batteries, while fixed GPUs provide power to parked aircraft through a permanent installation. Electric GPUs, although more expensive to purchase, offer a more sustainable option with reduced noise and CO2 emissions. A study by Zurich Airport found that the use of mobile GPUs, and even more so eGPUs, FEGPs, and PCAs, results in significant CO2 savings, lower power consumption, and reduced noise and emissions.
The cost implications of using GPUs and ground air are evident when considering the fuel burn rate of APUs. Most APUs burn 200-250 lbs per hour under a full load, equivalent to 31-39 gallons per hour. At Delta's average jet fuel prices over the last five years, ranging from $1.05 to $2.40 per gallon, the cost to cool an airplane during a one-hour turn ranges from $32.55 to $93.60.
To minimize costs, it is essential to consider not only the fuel burn rate but also the start cycle. Turning on the APU early may seem like an unnecessary expense, but it can be more cost-effective than letting engines idle or having multiple planes waiting with engines running due to understaffed ground crews. Additionally, when calculating fuel requirements, it is common to add 200 lbs per hour for every hour the APU is expected to run, ensuring that the aircraft has sufficient fuel to cover the APU's fuel burn.
In conclusion, while GPUs and ground air do incur costs, the use of GPUs can also lead to cost savings and environmental benefits by reducing fuel consumption and emissions. Therefore, when considering the costs of aircraft operations, it is essential to evaluate the overall efficiency and sustainability of different power sources, including both APUs and GPUs.
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APU usage is often poorly tracked
The APU, or auxiliary power unit, is a generator that provides electrical power to important systems of an aircraft when the engines are not running. It is used on the ground just prior to engine start and sometimes after landing. During an airborne engine failure, the aircrew can turn on the APU to ensure power is supplied to critical systems.
To track APU usage on the ground, airlines can use custom ACARS messages configured to be sent each time the APU is turned on or off, containing general APU information such as runtime, cycles, and fuel consumption. FDR data can also be used during turnaround, although this usually only records when at least one engine is running. Some providers offer the possibility of keeping FDR recording during the whole turnaround phase, providing APU information to airlines.
By monitoring APU usage, airlines can reduce fuel costs by limiting APU usage in favor of Airport Ground Power Units (GPU) when possible. GPUs use less than 20 kg of fuel per hour, significantly less than APUs. Tracking unreasonable APU usage during aircraft maintenance periods can also help reduce fuel costs.
Overall, by correctly monitoring APU usage and implementing fuel efficiency strategies, airlines can improve fuel efficiency and reduce emissions.
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APU burn rate depends on power and cooling load
The APU burn rate depends on several factors, including power requirements and cooling load. For example, an idling engine typically uses 0.8 to 1 gallon per hour, while a Carrier APU's fuel consumption varies between 0.1 and 0.3 gallons per hour, depending on the power and cooling requirements.
In the case of aircraft, the APU burn rate can be influenced by factors such as the aircraft model, ambient temperature, and the duration of ground operations. For instance, a Boeing B737-800 APU has an hourly fuel burn rate of approximately 225 lbs or 102 kg, while an A320 APU burns 126 kg of fuel per hour.
Pilots and ground crews must consider these factors when determining the appropriate amount of additional fuel to request or add. For instance, during winter de-icing operations, it is common to add 100 lbs of taxi fuel to account for potential delays. Similarly, when an aircraft is expected to sit at the gate with the APU running for 45 minutes to an hour, it is advisable to add 200 lbs of fuel to the original request.
It is worth noting that airlines have traditionally struggled to accurately track APU fuel usage on the ground, often underreporting utilisation rates. However, with growing awareness of the environmental and economic benefits of reducing fuel consumption, there is an increasing emphasis on monitoring and optimising APU usage, particularly during ground operations.
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Frequently asked questions
The fuel burn rate of a carrier APU is estimated to be between 200-250 lbs per hour or 31-39 gallons per hour under a full load.
An idling engine typically uses 0.8 to 1 gallon per hour. While the exact fuel burn rate of a carrier APU is not known, it is estimated to be lower than that of an idling engine.
The fuel burn rate of a carrier APU depends on various factors, including power and cooling load.
The fuel burn rate of a carrier APU may vary depending on the specific model and size of the APU. For example, the Boeing 737 APU has a fuel burn rate of 110 kg/hour, while the A320 APU has a fuel burn rate of 126 kg/hour.
To estimate the fuel needs for a carrier APU, it is common to assume a fuel burn rate of 200 lbs per hour. This estimate can be adjusted based on the expected operating time and specific characteristics of the carrier APU.
