Modern aircraft are designed to operate under various stressors, one of which is weight. Although the exact capacity that each plane can tolerate differs significantly, an average-sized commercial aircraft typically holds 175,000lbs upon takeoff. With such immense weight applied to the vessel, it is critical for the flight crew to perform accurate calculations that can accurately determine the aircraft's center of gravity while also predicting if that point will change during flight. These requirements are called load and trim calculations, and this area of aircraft safety is tightly regulated by FAA mandates. In this blog, we will discuss the procedures and calculations associated with aircraft load in trim while also discussing the risks associated with improper estimations.
When loading any aircraft containing passengers, it is necessary to distribute the weight of individuals and cargo evenly. While these calculations have been performed historically by a loadmaster or dispatcher, modern systems implement automation and computer algorithms to best disperse passenger and cargo load. Once a loading plan has been implemented, it is documented in a loading instruction form, which is then given to the supervisor, who must approve it before takeoff. Another factor that significantly affects weight distribution and efficiency is the proper distribution of fuel. The determination of this is always done by the lead pilot, who will then document the details on load and trim sheets.
Load and trim sheets are necessary documentation that should be completed and filed before flights. Although much of this process is now automated with input into a computer, some crews still use the manual documentation system to log these actions. Manual forms are made specific to every aircraft, each containing an "envelope" inscribed on a graph that projects the loading profile considered safe for that plane. Before filing the document and taking off, the flight commander should ensure that the calculated ramp weight, takeoff weight, and landing weight all fit within the given safe zone.
Departure Control Systems (DCS) refers to the automated programs responsible for calculating the load and trim in most commercial airline operations. Some airlines have their own proprietary system designed explicitly for their inventory of aircraft, while others contract this task out to handling agents. Electronic calculation helps reduce error while also optimizing for efficiency, but rarely these systems may become unavailable, forcing the flight crew to revert to manual calculation and documentation. However, as a result of automation and contracting, many pilots and flight crews lack experience in load and trim calculations, leading to a potentially dangerous situation.
At the very least, miscalculating or incorrectly documenting load and trim data could cause the aircraft to perform suboptimally. It is estimated that optimizing for trim can result in a 1% improvement in fuel consumption, which translates to thousands of dollars saved over a long flight. Another consequence of an improperly distributed load is a tail strike, which occurs when the back fuselage strikes the runway during takeoff. Although the damage is generally not severe enough to cause catastrophic loss, the vessel must still land and be thoroughly inspected before returning to service.
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