The speed bug changes from indicated airspeed to Mach at which flight level?

The speed bug changes from indicated airspeed to Mach at which flight level?

• A. FL300
• B. FL316
• C. FL320
• D. FL340

Answer: (B)

The key idea is when to switch the speed reference from indicated airspeed to Mach. On most airliners, the speed bug (the target speed on the speed tape) uses indicated airspeed below a certain altitude, then switches to Mach above that point. This transition is known as the transition altitude, and it exists because at high altitudes air density drops and Mach becomes a more meaningful way to express speed than IAS. In standard atmosphere, this switch occurs at flight level 316, which is about 31,600 feet. So the speed bug changes from IAS to Mach right around that altitude. Below that level you’re controlling with IAS; above it you reference Mach to maintain consistent aerodynamic performance as you climb. Therefore, the flight level where the switch happens in this context is FL316.

The key idea is when to switch the speed reference from indicated airspeed to Mach. On most airliners, the speed bug (the target speed on the speed tape) uses indicated airspeed below a certain altitude, then switches to Mach above that point. This transition is known as the transition altitude, and it exists because at high altitudes air density drops and Mach becomes a more meaningful way to express speed than IAS.

In standard atmosphere, this switch occurs at flight level 316, which is about 31,600 feet. So the speed bug changes from IAS to Mach right around that altitude. Below that level you’re controlling with IAS; above it you reference Mach to maintain consistent aerodynamic performance as you climb.

Therefore, the flight level where the switch happens in this context is FL316.