Mach indication on the PFD occurs at which combination of values?

Mach indication on the PFD occurs at which combination of values?

• A. 0.40 Mach
• B. 0.45 Mach or 31,600 ft
• C. 0.50 Mach
• D. 0.55 Mach or 50,000 ft

Answer: (B)

Mach indication on the PFD appears when the flight reaches a practical speed reference for high-altitude flying. In this system, the readout comes on when you reach 0.45 Mach, or when you climb to about 31,600 ft, whichever occurs first. This dual trigger keeps the display useful: below the altitude where Mach is the meaningful guide, IAS is typically used, but once you’re high enough, Mach becomes the primary reference. So the correct condition is the one that specifies 0.45 Mach or 31,600 ft. The other options show different thresholds that don’t match when the PFD Mach readout becomes active.

Mach indication on the PFD appears when the flight reaches a practical speed reference for high-altitude flying. In this system, the readout comes on when you reach 0.45 Mach, or when you climb to about 31,600 ft, whichever occurs first. This dual trigger keeps the display useful: below the altitude where Mach is the meaningful guide, IAS is typically used, but once you’re high enough, Mach becomes the primary reference.

So the correct condition is the one that specifies 0.45 Mach or 31,600 ft. The other options show different thresholds that don’t match when the PFD Mach readout becomes active.