Oil System

For aircraft certified since 1978, full engine oil is typically included in an aircraft’s empty weight. This can be confirmed by looking at the Type Certificate Data Sheet. If full oil is to be included, the oil level needs to be checked and the oil system serviced if it is less than full. If the Aircraft Specifications or Type Certificate Data Sheet specifies that only residual oil is part of empty weight, this can be accommodated by one of the following two methods.

1. Drain the engine oil system to the point that only residual oil remains.

2. Check the engine oil quantity, and mathematically subtract the weight of the oil that would leave only the residual amount. The standard weight for lubricating oil is 7.5 lb/gal (1.875 pounds per quart (lb/qt)), so if 7 qt of oil needed to be removed, the technician would subtract 13.125 lb at the appropriate arm.

Miscellaneous Fluids

Unless otherwise noted in the Aircraft Specifications or manufacturer’s instructions, hydraulic reservoirs and systems should be filled, drinking and washing water reservoirs and lavatory tanks should be drained, and constant speed drive oil tanks should be filled.

Flight Controls

The position of such items as spoilers, slats, flaps, and helicopter rotor systems is an important factor when weighing an aircraft. Always refer to the manufacturer’s instructions for the proper position of these items.

Other Considerations

Inspect the aircraft to see that all items included in the certificated empty weight are installed in the proper location. Remove items that are not regularly carried in flight. Also look in the baggage compartments to make sure they are empty. Replace all inspection plates, oil and fuel tank caps, junction box covers, cowling, doors, emergency exits, and other parts that have been removed. All doors, windows, and sliding canopies should be in their normal flight position. Remove excessive dirt, oil, grease, and moisture from the aircraft.

Some aircraft are not weighed with the wheels on the scales, but are weighed with the scales placed either at the jacking points or at special weighing points. Regardless of what provisions are made for placing the aircraft on the scales or jacks, be careful to prevent it from falling or rolling off, thereby damaging the aircraft and equipment. When weighing an aircraft with the wheels placed on the scales, release the brakes to reduce the possibility of incorrect readings caused by side loads on the scales.

All aircraft have leveling points or lugs, and care must be taken to level the aircraft, especially along the longitudinal axis. With light, fixed-wing airplanes, the lateral level is not as critical as it is with heavier airplanes. However, a reasonable effort should be made to level the light airplanes along the lateral axis. Helicopters must be level longitudinally and laterally when they are weighed. Accuracy in leveling all aircraft longitudinally cannot be overemphasized.

Weighing Points

When an aircraft is being weighed, the arms must be known for the points where the weight of the aircraft is being transferred to the scales. If a tricycle gear small airplane has its three wheels sitting on floor scales, the weight transfer to each scale happens through the center of the axle for each wheel. If an airplane is weighed while it is on jacks, the weight transfer happens through the center of the jack pad. For a helicopter with skids for landing gear, determining the arm for the weighing points can be difficult if the skids are sitting directly on floor scales. The problem is that the skid is in contact with the entire top portion of the scale, and it is impossible to know exactly where the center of weight transfer is occurring. In such a case, place a piece of pipe between the skid and the scale, and the center of the pipe will now be the known point of weight transfer.

The arm for each of the weighing points is the distance from the center of the weight transfer point to the aircraft’s datum. If the arms are not known, based on previous weighing of the aircraft or some other source of data, they must be measured when the aircraft is weighed. This involves dropping a plumb bob from the center of each weighing point and from the aircraft datum, and putting a chalk mark on the hangar floor representing each point. The perpendicular distance between the datum and each of the weighing points can then be measured. In Figure 4-18, the distance from the nosewheel centerline to the datum is being measured on a Cessna 310 airplane. Notice the chalk lines on the hangar floor, which came as a result of dropping a plumb bob from the nosewheel axle centerline and from the datum. The nosewheel sitting on an electronic scale can be seen in the background.

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