Volume 33 | Thursday, July 22nd, 2021
Aircraft Performance and Applying Biases
Welcome back to Jump Seat. As a crucial factor in flight planning, aircraft performance rarely gets overlooked. But the performance of an aircraft changes over time which leads to necessary tweaks to the profile. Fortunately, these updates are easy and quick.
Performance capabilities for each aircraft come from the published Original Equipment Manufacturer (or OEM) performance manuals. Within each manual are values for fuel flow, speed, weight, and altitudes that allow for flight planning. However, some tails will differ from the values given in the manual due to engine manufacturing, age, wear, and more. Implementing aircraft biases will aid in adjusting for these differences.
The individual climb, cruise, and descent phases that are loaded for each aircraft can have a big impact on the performance output. Some of the biases previously set under the legacy flight planning tool should be fine-tuned to increase accuracy. To assist in this process, Suggested Values based on aircraft type have been added under the Aircraft Biases tab within the TailAddForm. 
If your flight plan differs in fuel burn or flight time from the actual flight, consider adjusting the Aircraft Bias options. The first two options will add either a set amount of fuel to the climb portion of the flight or a set amount of time, respectively. The third box is a percentage of fuel flow that is added to all phases of the flight and it is applied first, before climb and descent fuel amounts. For example, adding 5% fuel flow to an aircraft that burns 1000lbs per hour would result in an increased burn of 1050lbs per hour. In other words, an additional 5% of fuel needed per hour of flight. The last two boxes will add either a set amount of fuel to the descent portion of the flight or a set amount of time, respectively.

There are often instances when an operator desires faster climb speeds than what is published in the OEM data which leads to requests for faster climb schedules in the system. However, the performance changes associated with higher climb speeds can often be accomplished and fine-tuned for a specific aircraft by using biases. Increased climb speeds typically result in longer climb times and higher climb burns due to a lower angle of attack. Simply adding biases to the climb phase can generate climb time and fuel calculations that more closely align with the higher climb speeds desired in real-world operations.

Additionally, taking the steps to confirm that your aircraft equipment codes are complete and accurate will help mitigate issues that are often misdiagnosed as performance-related. The flight planning engine employs built-in logic to review aircraft capabilities before suggesting routes or assigning altitudes. For example, the recent European Data Link Services Implementing Rule requires aircraft operating above FL285 to be equipped for ATN CPDLC communications, unless exempt. Flight plans showing "J1" (ATN CPDLC capability) in Field 10a, or "CPDLCX" (a statement of exemption) in Field 18 DAT/ will be permitted to operate at higher altitudes. Therefore, a lack of those codes will force flight planning altitudes at or below FL280 in European airspace. To many, that could come across as a performance issue with the aircraft, but an altitude cap like this is often attributable to incorrect equipment codes. 

Any account admin may update flight planning fuel biases or equipment codes for a tail under the My Company tab. Should you need help with adjusting biases or equipment codes, please reach out to our 24/7 Flight Operations team at +1 410 266 2266 or flightops@arinc.com. This team can also put you in contact with one of our performance experts to ensure that your flight plans are as accurate as possible.
Did you know?
  • Aircraft biases can be locked to the default for all flight plans by an account admin or the biases can open to be changed for each flight plan.
  • Any applied biases are also factored into the flight plan to the alternate airport. This is a change from the previous logic embedded in the tool. 
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Thank you for reading!