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If you are given the clearance to "cross [FIX] at 250 knots", does this specifically mean :

1 ) Cross fix at 250 knots, and then after [FIX] your assigned speed is 250 knots until otherwise instructed.

or

2 ) Cross fix at 250 knots, and then after [FIX] speed is at your discretion.

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    $\begingroup$ At the FIX you will be at 250, that is the instruction, but that instruction is never given in isolation, so you will always have an indication what to expect next so the problem doesn't really arise. As part of an approach instruction, the pattern you are approaching would be at or below 10,000 and so have upper (and possibly lower) speed limits. If the ATC wants you at a specific speed for spacing or timing reasons, they will explicitly tell you "Maintain speed X". $\endgroup$
    – Paul Smith
    Jan 13 at 16:52
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If I, as the ATC, give the instruction Cross [FIX] at 250 knots the expectation is that you will:

  • At a distance from the fix adjust your speed to be at 250 knots at the [FIX]

  • Maintain that speed until you either get a:

    • Cancel speed restrictions or Resume profile speeds
    • Another speed instruction is issued
    • A STAR or SID speed instruction is passed and that instruction is followed until the next instruction or a Cancel STAR/SID speed restrictions

It is extremely rare for that instruction to be given to a departing aircraft (at least were I work). The controller is more likely to issue a Climb at 250kts. This automatically gets cancelled as soon as the aircraft levels out and any further climbs are at profile speeds.

The instruction can also be given to crusing aircraft as a procedural seperation tool, except the speeds are not in knots but Mach number usually. Cross [FIX] at Mach 0.85 or less this is used for converging tracks where the speed restriction only applies from then to maintain the procedural standard.

I have only used the cruise instruction in oceanic control but the arrival instruction every 5 minutes all day and never the departure instruction.

But other areas may use more regularly in departure.

Source: I am an Australian ATC

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  • $\begingroup$ Other than being a controller do you have a specific reference in an Australian ATC Procedures document or other document (Pilot/Controller guidance, etc) that specifically addresses the OP's question and directly supports your answer? Thanks $\endgroup$
    – 757toga
    Jan 15 at 1:10
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This is an interesting question in that there is no clear and inarguably authoritative guidance (specifically on point) regarding the exact question being asked. It's easy to imagine that different pilots, after receiving the specific clearance as asked in the question, could disagree on which of the two options is appropriate.

However, in my opinion, in the U.S., you would cross the [FIX] at 250 kts as per the controller's instruction, and then, in the absence of any other instructions (including flying a STAR/SID or another procedure containing published speed restrictions), you could fly the speed of your choice (of course adhering to any regulatory speed restrictions).

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    $\begingroup$ On a departure, I agree that this answer is correct. On an arrival, not at all. $\endgroup$
    – Ralph J
    Jan 12 at 4:23
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    $\begingroup$ @RalphJ the OP's question is not reliant on whether or not the aircraft is inbound or outbound. The question is simply what does the instruction "Cross [FIX] at 250 kts" mean after passing [FIX] (whether coming or going)? That specific phraseology does not compel a pilot to remain at 250 kts until reaching an intervening procedure with a different published speed or receiving a different instruction or clearance from ATC. $\endgroup$
    – 757toga
    Jan 12 at 5:19
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    $\begingroup$ 757toga is correct. The OP's question does not refer to departures, arrivals, SIDs, STARs, or OPDs. If a controller wants an aircraft to cross a fix at a particular speed and stay at that speed, the clearance should be, "cross [fix] at and maintain two five zero knots." $\endgroup$
    – RetiredATC
    Jan 13 at 2:40
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On a departure, you could speed up as desired (and otherwise allowed, i.e. once above 10,000') after crossing the specified fix.

On an arrival, ATC would expect you to maintain 250 knots until slowed by later instructions (issued by a controller or published as part of a procedure), or given "speed your discretion," or cleared for an approach (which cancels previously issued speed assignments unless they're restated with the approach clearance).

An aircraft that immediately slows after crossing the fix at 250 is going to surprise ATC, who will NOT be pleased! They're planning on a steady flow of aircraft all at 250 knots from that fix inbound to the airport. Outside of (i.e. prior to) that fix, speeds may be 280 or 300 or whatever - either "normal speed" or as assigned to set up the sequence - but after that fix, "everybody is doing 250" until ATC's next adjustment.

The not-really-an-exception to this would be on approach, when "maintain 180 knots to a 5 mile final" is common, but the whole point of that clearance phrased that way is that once you reach the 5 mile point, it's expected you'll slow to final approach speed... they just don't want you doing so farther out. But "maintain [speed] until {FIX}" and "cross {FIX} at [speed]" are distinct instructions used for different purposes.

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    $\begingroup$ I respectfully disagree with your answer indicating that ATC "expects" a pilot to maintain 250 kts when inbound until (the points you mention). The OP's question was what does the specific ATC instruction (in the question) require the pilot to do not what ATC expects. "Cross [FIX] at 250 kts" is not the same as something like "Cross [FIX] at and maintain 250 kts. There are many arrival scenarios where a pilot will begin slowing from 250 prior to a new ATC speed assignment or approach clearance. If 250 is required by ATC it will be an assignment not just an expectation. $\endgroup$
    – 757toga
    Jan 12 at 5:00
  • $\begingroup$ I respectfully disagree with 757toga. STARs frequently include this type of instruction at busy airports to get the line slowed and at the same speed. They will then usually slow you down further verbally (210, then 180 is common) to make the spacing work turning final. $\endgroup$
    – 4redwings
    Jan 12 at 19:10
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    $\begingroup$ @4redwings I totally agree with you. Any published speed on a STAR needs to be adhered to. Then at busy airports further speed assignments will be made by ATC using words like "maintain" or "reduce to" (some speed). My comment to this answer (above) is only related to the issue of the diffence between an ATC expectation of a specific speed and an ATC assignment of a speed. $\endgroup$
    – 757toga
    Jan 12 at 19:27
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    $\begingroup$ Most controllers will not expect an arrival that had been restricted to cross a fix at 250K to speed up afterward when they will be reduced to a slower speed later as they are sequenced with other arrivals. Most pilots, knowing they are going to be given a speed reduction soon, would not speed up either. The reality is that without "maintain" there is nothing to keep the pilot from increasing the aircraft speed. $\endgroup$
    – RetiredATC
    Jan 13 at 2:53
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If unsure what happens next, ask the ATC.
For the FAA, it's all covered clearly under Speed Adjustment in the ATC Job Order.

The general expectation is:

Controllers should anticipate pilots will begin adjusting speed at the minimum distance necessary prior to a published speed restriction so as to cross the waypoint/fix at the published speed. Once at the published speed, controllers should expect pilots will maintain the published speed until additional adjustment is required to comply with further published restrictions or ATC assigned speed restrictions. [bold emphasis added]

If the cross at speed is different than published, then it's an amended crossing speed and the same expectation applies.

If you're to maintain the speed regardless of further published restrictions, the ATC will be clear; an example from the linked FAA document:

“Descend via the KEPEC Two arrival, except after NIPZO maintain one eight zero knots.” [bold emphasis added]

There are various other situations, so do check the document.

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