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There's a big difference between ATC issuing you an "immediate" vs. "best rate" descent. Here's how to handle these 8 common phrases...

1) "Climb" or "Descend"

The most basic instruction is ATC simply directing you to "climb" or "descend" to a particular altitude. Climb at the optimum rate for your airplane. If you're unable to climb at a rate of at least 500 FPM, advise ATC.

2) "Pilot's Discretion"

According to the FAA, when ATC issues a clearance to climb/descend at pilot's discretion (PD), pilots may begin the climb/descent whenever they choose, and at any rate of their choosing. Pilots are also authorized to level off, temporarily, at any intermediate altitude. However, once the aircraft leaves an altitude, it may not return to that altitude.

3) "Cruise"

"N216BD Cruise 8,000'." When ATC issues this clearance, the block of airspace between the minimum IFR altitude to the altitude in your clearance is yours to use. You can climb, descend, and level off at any intermediate altitude within the block of airspace, all the way to your destination under IFR. You're responsible for determining the minimum IFR altitude in your area. Traffic separation is still provided by ATC.

4) "Expedite" Climb/Descent

When ATC issues the instruction, "expedite climb", it normally indicates that the pilot should use the approximate best rate of climb without an exceptional change in aircraft handling characteristics. The same goes for descents. Most controllers will let you know why they're expediting your descent/climb.

5) "Best Rate"

If you hear "best rate," ATC is requesting you to maximize your vertical climb/descent rate. Maintaining momentum and forward speed goes out the window when you hear this instruction, and you should focus on increasing your vertical speed safely.

6) "Good Rate"

Similarly, "good rate" means ATC wants you to increase your vertical climb/descent rate above a normal threshold. They're not asking for maximum performance, but rather a noticeably steeper vertical path.

7) "In ___ Minutes Or Less" (Timed)

You may hear ATC ask if you can make an altitude within certain time constraints. Quickly analyze your current vertical speed and performance to see if you can make it. Start a timer to double-check your work.

8) "Immediately"

"Immediately" is used to convey urgency from ATC to avoid an imminent situation. Immediate action with a substantial climb or descent is necessary for safety when you hear this phrase.

What else have you heard from ATC? Tell us in the comments below.

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