How do I plan for ATC24’s 185-knot speed restriction below 3,000 feet?

Below 3,000 feet, all aircraft in ATC24 have a maximum speed of 185 knots. Treat that as 185 KIAS, not ground speed: decelerate before descending through 3,000 feet, preferably targeting a small buffer such as 180–183 KIAS, and do not wait until crossing the altitude boundary to select the lower speed.

For ATC24 in our Aviation & Real-World Flying context, this is a simulator-specific rule rather than a universal real-world speed limit. Actual limits vary with jurisdiction, airspace, aircraft limitations, published procedures and ATC instructions.

Below 3,000 feet, what is ATC24’s maximum speed?

The real answer is 185 knots, or 185 KIAS, for all aircraft operating below 3,000 feet in ATC24.

Maximum means the aircraft may fly slower, but it must not exceed 185 knots. There is no exemption simply because an aircraft is a fast jet. A lower charted speed, aircraft limit or ATC restriction still applies; for example, a maximum of 170 knots remains 170 rather than becoming 185.

The wording says below 3,000 feet, but crossing the boundary fast and then trying to decelerate is not a workable interpretation. The mistake we see constantly is selecting 185 at 3,000 feet instead of arriving at the boundary already stabilised below the limit. Use the altitude reference specified by the ATC24 procedure or session rules rather than substituting height above the ground.

Is 185 knots indicated airspeed or ground speed?

Use indicated airspeed unless ATC24 explicitly labels the value differently.

The IAS shown on the primary flight display or airspeed indicator determines compliance. Ground speed is still useful for calculating how many nautical miles the aircraft will travel while slowing, but a tailwind does not permit more than 185 KIAS and a headwind does not reduce the limit.

How fast is 185 kts in mph?

185 knots is approximately 213 mph, 343 km/h or 95.2 m/s.

These are unit conversions, not alternate instruments for checking the restriction. Continue to monitor KIAS in the cockpit.

How far before 3,000 feet should I start slowing?

Start early enough to reach no more than 185 KIAS before descending through 3,000 feet, with extra distance for wind, aircraft mass and any simultaneous descent.

1. Confirm the applicable limit. Check for a lower procedure or ATC speed and distinguish a maximum from an instruction to maintain an exact speed. If the restriction comes from a procedure, brief the chart using our explanation of how to interpret SID and STAR speed constraints.
2. Calculate the speed to lose. Use present KIAS − 185. An aircraft at 240 KIAS must lose 55 knots; one already at 175 KIAS needs no reduction, only protection against acceleration.
3. Estimate deceleration from the aircraft you are flying. There is no trustworthy distance that applies to every ATC24 aircraft. Use its demonstrated deceleration rate in the intended configuration, then calculate distance (NM) = ground speed × time in minutes ÷ 60.
4. Allow for descent energy. A clean aircraft usually slows less readily while descending because gravity is helping it retain speed. Reduce the descent angle, slow before starting down or reserve a level segment when clearance and terrain permit.
5. Build in a buffer. Aim for roughly 180–183 KIAS when the instruction is a maximum of 185. This absorbs small autopilot, thrust and turbulence-related overshoots.
6. Monitor the result. Watch actual IAS trend and distance remaining. Selecting 185 on an autopilot or FMC commands a target; it does not guarantee that the aircraft has enough drag to achieve it.

A speed plan never authorises an early descent. If ATC or the procedure controls your descent, review when a descent may begin after clearance before leaving the assigned altitude.

Worked example: slowing from 240 to 185 knots

At 240 KIAS, the required reduction is 55 knots. If that aircraft has demonstrated a deceleration rate of 30 knots per minute in the planned configuration, slowing takes about 1.8 minutes. At an average ground speed of 220 knots, that represents approximately 6.7 NM before adding a safety margin.

If the same aircraft must descend from 8,000 feet to 3,000 feet, a basic three-degree estimate gives about 15 NM:

5,000 feet ÷ 1,000 × 3 = 15 NM

A conservative first plan reserves about 7 NM for deceleration and 15 NM for descent, then adds margin. A capable FMC may blend the two phases into less distance, but do not assume simultaneous descent and deceleration will work until the aircraft’s actual energy trend confirms it.

For an ATC24 controller, the same calculation works backwards from the aircraft’s groundspeed. Issue the reduction with enough lead time; assigning 185 knots when traffic is already passing 3,000 feet at 220 knots cannot produce instant compliance.

How does Mach-speed deceleration fit into the restriction?

Complete the transition from Mach-based high-altitude flight to IAS-based control well before entering the terminal area.

Mach and IAS are not interchangeable fixed numbers. Their relationship changes with altitude and atmospheric conditions, so there is no single Mach setting that always equals 185 KIAS. During descent, verify that the active speed mode has changed to IAS and that the displayed target is 185 knots or lower before crossing 3,000 feet.

A high-speed aircraft may show a comparatively modest IAS while travelling at a high Mach number at altitude. Near 3,000 feet, however, the ATC24 restriction is handled as an indicated-air-speed limit; ground speed and the earlier cruise Mach do not determine compliance.

What should I do if a 737 is off schedule on descent?

If a Boeing 737 is high, fast or both, reduce the rate of descent or level temporarily when authorised rather than continuing downhill and expecting 185 knots to appear.

• Confirm that the active automation mode is commanding IAS rather than Mach and that thrust has reduced as expected.
• Trade descent rate for deceleration. A shallower path gives drag and lower thrust more time to remove speed.
• Use speed brakes only within the aircraft’s limits and normal procedures; our guide to using speed brakes without creating a configuration problem explains the main traps.
• Do not extend flaps above their placard speeds or assume that 185 KIAS automatically calls for a particular flap setting.
• If compliance has become impossible, report that early or discontinue an unstable approach instead of forcing the aircraft through the restriction.

A tailwind, high mass, a steep vertical path and late thrust reduction are common causes. Our practical advice on controlling speed and descent energy in a simulated 737 covers the follow-up problem of overshooting the selected speed.

Does the 185-knot rule limit an SR-71’s highest speed in MSFS?

No; ATC24’s below-3,000-foot rule is not a general Microsoft Flight Simulator speed cap, and an SR-71 maximum-speed attempt belongs at high altitude rather than near the ground.

In MSFS, use the checklist and operating limits supplied with the particular SR-71 model because add-ons differ in their engine, inlet and afterburner simulation. Climb using the model’s prescribed profile, clean up the gear, flaps and speed brakes, confirm that full throttle and afterburner inputs register, and judge the high-speed phase by Mach rather than trying to maximise low-altitude IAS.

If the aircraft will not accelerate as expected, check for residual drag, throttle calibration, icing, damage or failures, excessive payload and assistance settings that may be limiting control inputs. Do not chase a quoted top-speed figure below 3,000 feet: dense air produces far more drag and dynamic pressure, while the 185-knot figure on this page applies specifically to ATC24 traffic operating under its low-altitude rule.