I couldn't find any information on this topic. Do Speed Restrictions depicted on Jeppesen Approach Charts have plus or minus limitations for any restriction we see on the charts? Do we have to exactly keep that speed? Not even a 1 knot boundary?
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1$\begingroup$ Can you give a specific example of exactly what speeds you are referring to? Are you asking only about speeds shown on "instrument approach" charts, or are you including "STARs" (standard terminal arrival routes) and/or "SIDs" (standard instrument departures)? Thanks $\endgroup$– user22445Jul 7 at 15:06
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2$\begingroup$ The fact that the charts are published by Jepp or any other entity is a red herring, IMO. The procedures depicted on the charts are created by a given country's ANSP and you will have to check that country's guidance for what their tolerances are. $\endgroup$– randomheadJul 7 at 15:12
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$\begingroup$ @757toga Actually, i thought the answer would be general including all charts. But, you are right. Effect of deviation from restriction probably differ from Approach Chart to SIDs or STARs. Since I couldn't find any sources of information on this I am open to all kinds of information :) Thanks in advance. $\endgroup$– tekin beyazJul 7 at 16:59
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1$\begingroup$ @Timbo There are often speed restrictions on IAPs, SIDs, and STARs. Check out LAX ILS or LOC RWY 7R IAP, GOATZ ONE ARRIVAL, and SKWRL TWO DEPARTURE, for example. $\endgroup$– user22445Jul 8 at 19:08
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1$\begingroup$ @757toga, thanks! $\endgroup$– TimboJul 9 at 2:16
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2 Answers
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Speeds in the chart, along with altitudes and (when part of the procedure) headings, are assignments by ATC, much like a controller directing an aircraft to "maintain 3,000' and fly heading 180."
Obviously, flying at 3,001 feet and heading 181 isn't likely to be considered a violation of the clearance -- nobody out there would still be flying if it were. Tolerances are specified elsewhere, not in Jeppesen charts, and as @randomhead pointed out in the comments, Jepp simply reproduces what each nation gives them, in a standard format.
Typical ATP tolerances are plus/minus 10 degrees, 100 feet, and 10 knots. Since most instrument procedures (once the training is complete) are flown with a flight director or autopilot (and, often, auto throttles), the expectation is that you set the 250 knots (or whatever speed is called for) in the system, and you (or the automation) strive to hold that speed. If you get off of it a little bit, you make the appropriate correction. If you're assigned 250 and you're chugging along at 265 and not correcting, then you're not doing what you should be.
Whether you'll get called out on that deviation or not is highly dependent on context, who's watching, and what equipment they have to see exactly what it is you're doing. If "your" 250 knots is significantly faster or slower than other aircraft on the same arrival also doing "250 knots" then ATC will probably notice; if they don't have ADSB reporting your exact speed and you're the only aircraft out there, the controller will probably assume there's a headwind or tailwind affecting your groundspeed and probably won't worry much about it.
Slight related:
There's an old story about a particular airline that was known for going pretty fast back in the day, and a particular captain who flew around fast all the time. He's on an arrival, flying at his usual speed of heat, and ATC asks his airspeed. The FO replies with their speed, and they're told to slow to 280 knots. The captain does no such thing, and a few minutes later they're told to slow to 250 knots. The FO dutifully reads back the clearance, and the captain changes nothing. Finally ATC asks them to "say airspeed," to which the captain tells the FO to "Tell 'em we're doing 250." The FO isn't real keen about lying on the radio, but the captain is in charge...
"The captain says we're doing 250, sir"
The captain's head promptly explodes, with a great tirade of that's not what I told you to say, etc etc. The controller calmly replies, "well, your 250 is faster than {other airline}'s 300 knots, so your captain can either slow down, or I'm going to have to give you vectors out over North Dakota for spacing."
I have no idea if they actually slowed down enough to avoid the vectors, or not.
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$\begingroup$ Thanks! Great story and an example of CRM maybe. :) Where can I find those tolerances? ICAO Annexes? $\endgroup$ Jul 9 at 8:06
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1$\begingroup$ @tekinbeyaz The ATP "tolerances" RalphJ is referencing in his answer are proficiency/skill based tolerances when taking a flight check (such as for the ATP certificate). If those tolerances are consistently exceeded during the check ride, the examiner may fail the applicant. Those "tolerances" are not related to "plus or minus limitations" associated with speed restrictions depicted on IFR Charts (which [tolerances] in the U.S. do not exist) as noted in my answer below. If you want to know the location where the ATP check ride tolerances are shown I can post a comment link. $\endgroup$– user22445Jul 9 at 15:47
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NOTE: In answering your question, I'm assuming that you are referring to a "regulation-based" or official procedural-based limitation/speed range that applies to "depicted" speed restrictions published on Instrument Charts.
In the U.S., there are no regulation-based "ranges" (plus or minus limitations) for speeds depicted/published on Instrument Charts (e.g. SIDs, STARs, IAP's, etc.). For example, if a speed to cross a particular fix on a STAR is depicted as 280 kts, there is not a published regulation-based "range" that applies to that speed (e.g., +/- 10 kts).
Of course, pilot skill, turbulence, etc. can influence the actual speed at which the fix is crossed.