Maximum allowable error

• A. +- 75 feet (FAA). Aviators should check operator or maintenance manual to confirm accurate limit for their aircraft
• B. +- 100 feet
• C. +- 150 feet
• D. +- 25 feet

Answer: (A)

Understanding permissible instrument error means knowing how far an instrument’s reading may deviate from the true value and still be considered acceptable after proper calibration. For the altimeter, the FAA requires the indicated altitude to be within plus or minus 75 feet of the actual altitude under standard testing conditions. This tolerance helps ensure reliable altitude information for safe flight planning and terrain clearance. Remember that the exact limit can vary with specific aircraft and equipment, so always check the operator’s or maintenance manual for the precise tolerance for your airplane. Other numbers like 100, 150, or 25 feet fall outside the typical FAA tolerance for a standard altimeter.