FAA Airline Transport Pilot (ATM)Aircraft Performance and Weight and BalanceHard
An airline's weight and balance system uses an index system referenced to a fixed datum, where the current index number is 40.0. A loadmaster adds 2,000 lb of cargo to a compartment where the loading chart shows an index contribution of 15.0 index units per 1,000 lb loaded at that station. What is the new total index number after this cargo is loaded?
- A85.0
- B70.0
- C62.5
- D55.0
Show answer & explanationAnswer & explanation
Correct answer: B. 70.0
The index contribution is 15.0 units per 1,000 lb. Loading 2,000 lb contributes 2 × 15.0 = 30.0 index units. Adding this to the current index of 40.0 gives a new total index of 40.0 + 30.0 = 70.0.
Why the other options are wrong
- A. 85.0 overstates the index contribution for the given weight.
- C. 62.5 does not correspond to any correct multiplication of the given index rate.
- D. 55.0 would result from adding only 15.0 units, ignoring the 2,000 lb quantity.
Weight and Balance Index System
An index system converts moments (weight × arm) into simplified index units referenced to a datum, allowing loadmasters to track CG changes with simple addition/subtraction instead of large moment numbers.
- Index units simplify large moment values (e.g., moment/reduction constant K).
- Each loading station has a published index rate per unit weight.
- Adding weight forward or aft changes the index by weight × station index rate.
- Final index is checked against CG limit charts to verify airplane is within limits.
Memory trick: Index units are the 'shorthand' for moments — multiply weight by the station's rate, add to the running total.