Our Ask a Tech feature for this month addresses a common snag that tags along with older aircraft that have seen some upgrades over the years. While major work like avionics retrofits, engine upgrades and even paint generally require a revision to the aircraft’s weight and balance report, it doesn’t always get done. And even when it does, the end result is only as accurate as the data the technician has to work with.
A reader with a new-to-her Cessna is skeptical about the accuracy of the data in the existing weight and balance report and the shop suggested she have the plane weighed. That’s the right answer. Here’s what it takes.
Not complicated work
It isn’t exactly cheap, either, and pricing seems to vary widely by region and by aircraft type. But it’s worth it for some, and I’ve seen enough weight and balance reports to know why there are often gross inaccuracies that need to be corrected.
When preparing to make a revision to the weight and balance, it’s not uncommon to discover equipment that was installed and removed from some aircraft without being documented. For these, computing a new report for these aircraft is pointless. After all, you need to start a revision with accurate basic empty weight and reference datum figures. In many cases, the only way to do that is to have the aircraft weighed.
But who’s gonna do it? While aircraft weighing is specialty work, the process is easier than you might think if you find the right shop. That includes using a weighing service that has certified and calibrated scales that are designed specifically for weighing aircraft. Some shops offer mobile services where they’ll bring the scales to your location so you don’t have to fly it to them. You’ll pay a premium for this service. Moreover, no one set of scales is appropriate for all aircraft. It could require an investment of $35,000 for the modern equipment that’s needed to weigh a variety of aircraft, including jets. The equipment generally consists of multiple scales with wireless transmitters and can include a combination of sensors, including jack stand load cells and platform scales.
The setup in the main picture is from the respected USA Measurements, which offers a variety of scales. Shown under the Cessna in image above is an Airweigh Plane Scale system that’s priced around $4500. This uses a 24- by 16-inch platform scale with three weighing pads and the system is good for up to 20,000 pounds. It includes a receipt printer to spit out the new report.
That’s not negligible
Several weighing services told me there are some warning signs that a report might be inaccurate. One red flag is a retrofit signed off with the statement “negligible change to weight and balance,” which should be suspect because that’s rarely the case. Some technicians follow the under-1-pound rule; if the removed or installed equipment is less than 1 pound, they might not compute a new weight and balance report. For that reason, many aircraft gain weight over time. Truth is, whether it’s a paint job that didn’t include a complete strip of the old paint, or avionics that were installed or removed without factoring the weight of wire and hardware (wiring adds or reduces a lot of weight), 1 pound here and there can add up over time.
But even aircraft that are weighed might still might not have accurate reports. Do your part and empty the aircraft of everything that’s not on the original type certificate before having it weighed. Some shops might top off the fuel tanks before weighing it and subtract the weight of the fuel from the report. If the airplane is turbine-powered, it will generally have to be defueled because the density of jet fuel changes with temperature.
Shopping for a used plane? Look hard at the data and speak up if it doesn’t seem right. Someone will have to pay to correct it, and that could mean shelling out $800 to $1000, on average, for a piston single.
