FAA Aviation Mechanic General (AMG)Aircraft Drawings, Weight and BalanceHard
A technician installs a 20 lb avionics unit at fuselage station 150 (arm = 150 inches aft of datum) during a weight and balance revision. What moment does this installation add to the aircraft's total moment?
- A20 in-lb
- B7.5 in-lb
- C150 in-lb
- D3,000 in-lb
Show answer & explanationAnswer & explanation
Correct answer: D. 3,000 in-lb
Moment is calculated as weight multiplied by arm: 20 lb × 150 in = 3,000 in-lb. This moment value is what gets added to the aircraft's total moment when computing the new CG after the installation.
Why the other options are wrong
- A. This is just the weight value, not the moment.
- B. This results from dividing weight by arm, which is not how moment is calculated.
- C. This is just the arm value, not the moment (weight × arm).
Moment (Weight & Balance)
The turning effect of a weight about the datum, calculated as weight multiplied by its arm (distance from datum).
- Moment = Weight × Arm
- Expressed in inch-pounds (in-lb)
- Used to find total moment for CG calculations
Memory trick: Moment = Weight times Wobble-distance (arm).