FAA Aviation Mechanic General (AMG)Physics, Math and Fluid LinesEasy
A technician calibrating an altimeter test set needs to convert standard sea-level atmospheric pressure to inches of mercury. Standard pressure is 14.7 psi, and 1 psi is approximately equal to 2.036 inHg. What is the standard sea-level pressure in inches of mercury?
- A33.90 inHg
- B14.70 inHg
- C29.92 inHg
- D760.0 inHg
Show answer & explanationAnswer & explanation
Correct answer: C. 29.92 inHg
Multiply psi by the conversion factor: 14.7 psi × 2.036 inHg/psi ≈ 29.93 inHg, which rounds to the familiar standard of 29.92 inHg used in altimetry.
Why the other options are wrong
- A. This value is the mmHg conversion factor confused with inHg.
- B. This is the pressure value in psi, not converted to inHg.
- D. 760 is the standard pressure in millimeters of mercury, not inches.
Pressure Unit Conversion
Standard atmospheric pressure can be expressed in multiple units: 14.7 psi, 29.92 inHg, or 760 mmHg, all representing the same sea-level condition.
- 1 psi ≈ 2.036 inHg
- Standard sea-level pressure = 14.7 psi = 29.92 inHg = 760 mmHg
- Altimeters and barometers are calibrated using inHg in the US
Memory trick: 'Fourteen-seven gives twenty-nine-ninety-two' — the aviator's pressure pair.