[{"data":1,"prerenderedAt":308},["ShallowReactive",2],{"learn-\u002Flearn\u002Ftop-of-descent-and-the-3-to-1-rule":3,"learn-nav-\u002Flearn\u002Ftop-of-descent-and-the-3-to-1-rule":285},{"id":4,"title":5,"body":6,"date":214,"description":215,"draft":216,"extension":217,"faqs":218,"howTo":228,"keyTakeaways":236,"meta":241,"navigation":242,"path":243,"quiz":244,"seo":269,"series":270,"seriesOrder":270,"sources":271,"stem":282,"topic":283,"__hash__":284},"learn\u002Flearn\u002Ftop-of-descent-and-the-3-to-1-rule.md","Top of descent and the 3:1 rule",{"type":7,"value":8,"toc":204},"minimark",[9,27,33,38,46,53,57,81,84,88,94,107,110,114,125,151,158,162,193,197],[10,11,12,13,20,21,26],"p",{},"A jet does not stop in the air, so a descent that starts in the wrong place ends with either a long level slog or a rushed, steep dive onto the approach. The ",[14,15,19],"a",{"href":16,"className":17},"\u002Flearn\u002Fglossary#gt-3-1-rule",[18],"glossary-link","3:1 rule"," is the mental arithmetic that puts the ",[14,22,25],{"href":23,"className":24},"\u002Flearn\u002Fglossary#gt-top-of-descent",[18],"top of descent"," in the right place, and it is worth knowing whatever you fly.",[28,29,30],"blockquote",{},[10,31,32],{},"This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.",[34,35,37],"h2",{"id":36},"the-31-rule","The 3:1 rule",[10,39,40,41,45],{},"The rule is simple: ",[42,43,44],"strong",{},"allow 3 nautical miles of track distance for every 1000 feet you need to lose."," Multiply the height to lose, in thousands of feet, by three, and that is roughly how far out to begin the descent.",[10,47,48,49,52],{},"Three miles per thousand feet works out to a steady path of ",[42,50,51],{},"roughly 3 degrees",", which is the same gentle angle used for a normal instrument approach. It is shallow enough to be comfortable and to keep the engines doing useful work, and steady enough that you can hold it without constant correction.",[34,54,56],{"id":55},"where-the-rule-comes-from-60-to-1","Where the rule comes from: 60-to-1",[10,58,59,60,63,64,70,71,76,77,80],{},"The 3:1 rule is a handy face of the ",[42,61,62],{},"60-to-1 rule",", the geometry the ",[14,65,69],{"href":66,"rel":67},"https:\u002F\u002Fwww.faa.gov\u002Fregulations_policies\u002Fhandbooks_manuals\u002Faviation\u002Finstrument_procedures_handbook",[68],"nofollow","FAA Instrument Procedures Handbook"," leans on for vertical planning. At a distance of 60 nautical miles, an angle of 1 degree subtends about 1 ",[14,72,75],{"href":73,"className":74},"\u002Flearn\u002Fglossary#gt-nautical-mile",[18],"nautical mile",". Brought down to per-mile terms, ",[42,78,79],{},"1 degree of slope is about 100 feet of height per nautical mile",", so a 3 degree path loses about 300 feet per mile.",[10,82,83],{},"Turn that around and 300 feet per mile is close to 1000 feet every 3 miles, which is the 3:1 rule. The two are the same relationship seen from different ends, and the small rounding is why the rule is a planning aid, not a promise.",[34,85,87],{"id":86},"finding-the-top-of-descent","Finding the top of descent",[10,89,90,91,93],{},"To place the ",[42,92,25],{},", work out the height to lose and apply the rule:",[95,96,97,101,104],"ul",{},[98,99,100],"li",{},"Take your cruise altitude and subtract the altitude you need at the planned point.",[98,102,103],{},"Multiply that height to lose, in thousands of feet, by three to get the distance in nautical miles.",[98,105,106],{},"Add a margin of track miles to slow from cruise speed down to a clean approach speed, since deceleration also eats distance.",[10,108,109],{},"Measure that total back from the target point and you have the top of descent.",[34,111,113],{"id":112},"a-worked-example","A worked example",[10,115,116,117,120,121,124],{},"Say you are cruising at ",[42,118,119],{},"FL350"," and need to cross a fix at ",[42,122,123],{},"5000 feet",".",[95,126,127,134,140],{},[98,128,129,130,133],{},"The height to lose is 35,000 minus 5000, which is ",[42,131,132],{},"30,000 feet",", or 30 thousands.",[98,135,136,137,124],{},"Distance to descend is 30 times 3, which is ",[42,138,139],{},"90 nautical miles",[98,141,142,143,146,147,150],{},"Add roughly ",[42,144,145],{},"10 nautical miles"," to decelerate from cruise toward approach speed, so plan the top of descent about ",[42,148,149],{},"100 nautical miles"," before the fix.",[10,152,153,154,157],{},"To hold the path once you are descending, use the rate-of-descent shortcut: ",[42,155,156],{},"about five times your groundspeed in knots, in feet per minute",". Early in the descent at 450 knots groundspeed that is about 2250 feet per minute; as you slow, the rate you need falls with the groundspeed. A good in-descent check is to divide the height still to lose by the miles still to run: if you have 10,000 feet to lose in 30 miles, you need about 333 feet per mile, which is right on a 3 degree profile.",[34,159,161],{"id":160},"common-pitfalls","Common pitfalls",[95,163,164,170,176],{},[98,165,166,169],{},[42,167,168],{},"Forgetting the deceleration miles."," The 3:1 distance gets you down, but slowing from cruise to approach speed needs extra track miles on top.",[98,171,172,175],{},[42,173,174],{},"Ignoring the wind."," A strong tailwind raises your groundspeed, so you need a higher rate of descent and you cover the ground faster, both of which argue for starting down a little earlier.",[98,177,178,181,182,187,188,192],{},[42,179,180],{},"Letting the path go high."," Once you are above profile it is hard to recover without speed brakes or a steep, uncomfortable rate, so it is better to start down on time and adjust gently, a point ",[14,183,186],{"href":184,"rel":185},"https:\u002F\u002Fskybrary.aero\u002Farticles\u002Fenergy-management-during-approach",[68],"SKYbrary"," makes about managing energy on the way down. Plan to be stable and configured by the ",[14,189,191],{"href":190},"\u002Flearn\u002Fstabilised-approaches-and-cdfa","approach gates"," your operator uses.",[34,194,196],{"id":195},"in-pilot-efb","In Pilot EFB",[10,198,199,200,203],{},"Pilot EFB includes ",[42,201,202],{},"top-of-descent and rate-of-descent calculators",", with the working shown so you can see how the height to lose, the distance and the groundspeed feed the answer. The figures are for your own planning; Pilot EFB is offline-first and is not a certified Electronic Flight Bag, so fly the profile and rates approved for your aircraft and follow ATC.",{"title":205,"searchDepth":206,"depth":206,"links":207},"",2,[208,209,210,211,212,213],{"id":36,"depth":206,"text":37},{"id":55,"depth":206,"text":56},{"id":86,"depth":206,"text":87},{"id":112,"depth":206,"text":113},{"id":160,"depth":206,"text":161},{"id":195,"depth":206,"text":196},"2026-06-21","How to work out your top of descent with the 3:1 rule, the 60-to-1 relationship behind it, and the rate of descent that holds a roughly 3 degree path, with a worked example.",false,"md",[219,222,225],{"q":220,"a":221},"What is the 3:1 rule for descent?","The 3:1 rule is a planning shortcut: allow 3 nautical miles of track distance for every 1000 feet you need to descend. To lose 30,000 feet you plan to start down about 90 nautical miles out, plus a few extra miles to slow down. It produces a steady path of roughly 3 degrees, which is comfortable for passengers and easy to fly.",{"q":223,"a":224},"How do you calculate your top of descent?","Take the height to lose in thousands of feet and multiply by three to get the distance in nautical miles. From cruise at FL350 down to 5000 feet that is 30,000 feet to lose, so 30 times 3 is 90 nautical miles. Add a margin to decelerate from cruise speed, and that distance back from your target point is the top of descent.",{"q":226,"a":227},"What rate of descent holds a 3 degree path?","A handy approximation is to multiply your groundspeed in knots by five to get the rate of descent in feet per minute for a roughly 3 degree path. At 450 knots groundspeed that is about 2250 feet per minute; as you slow down, the required rate falls with the groundspeed.",{"name":229,"steps":230},"Plan a descent with the 3:1 rule",[231,232,233,234,235],"Work out the height to lose: cruise altitude minus your target altitude at the planned point.","Multiply the height to lose in thousands of feet by three to get the descent distance in nautical miles.","Add a margin of track miles to decelerate from cruise to approach speed.","Measure that total distance back from the target point to find the top of descent.","In the descent, set a rate of about five times your groundspeed in knots to hold the path, and adjust to stay on profile.",[237,238,239,240],"The 3:1 rule allows 3 nautical miles of track distance for every 1000 feet to descend, producing a path of roughly 3 degrees.","Top of descent is the height to lose in thousands of feet times three, in nautical miles, plus a margin to decelerate.","A rate of descent of about five times groundspeed in knots holds a roughly 3 degree path.","The 3:1 rule comes from the 60-to-1 relationship, where 1 degree of slope is about 100 feet of height per nautical mile.",{},true,"\u002Flearn\u002Ftop-of-descent-and-the-3-to-1-rule",[245,253,261],{"q":246,"options":247,"answer":206,"explanation":252},"Using the 3:1 rule, how far out should you start down to lose 24,000 feet?",[248,249,250,251],"About 24 nautical miles","About 48 nautical miles","About 72 nautical miles","About 96 nautical miles","Multiply the height to lose in thousands of feet by three: 24 times 3 is 72 nautical miles, plus a margin to slow down.",{"q":254,"options":255,"answer":206,"explanation":260},"Roughly what rate of descent holds a 3 degree path at 300 knots groundspeed?",[256,257,258,259],"About 600 feet per minute","About 1000 feet per minute","About 1500 feet per minute","About 3000 feet per minute","Multiply groundspeed by about five: 300 times 5 is roughly 1500 feet per minute for a 3 degree path.",{"q":262,"options":263,"answer":206,"explanation":268},"What kind of descent path does the 3:1 rule produce?",[264,265,266,267],"A steep path of about 6 degrees","A shallow path of about 1 degree","A steady path of roughly 3 degrees","A level cruise with a late dive","Three nautical miles per 1000 feet works out to roughly a 3 degree path, which is comfortable and easy to fly.",{"title":5,"description":215},null,[272,274,277,280],{"label":273,"url":66},"FAA Instrument Procedures Handbook (FAA-H-8083-16B)",{"label":275,"url":276},"FAA Airplane Flying Handbook (FAA-H-8083-3C)","https:\u002F\u002Fwww.faa.gov\u002Fregulations_policies\u002Fhandbooks_manuals\u002Faviation\u002Fairplane_handbook",{"label":278,"url":279},"FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C)","https:\u002F\u002Fwww.faa.gov\u002Fregulations_policies\u002Fhandbooks_manuals\u002Faviation\u002Fphak",{"label":281,"url":184},"SKYbrary: Energy Management During Approach","learn\u002Ftop-of-descent-and-the-3-to-1-rule","Operations","y33nmmn62U0DSb3qh-OAI6CdpOzMZ5dr-uGw941bePs",{"related":286,"newer":296,"older":301,"series":270},[287,292,296],{"path":288,"title":289,"description":290,"date":214,"topic":283,"draft":216,"minutes":291,"series":270,"seriesOrder":270},"\u002Flearn\u002Fcold-temperature-altimeter-corrections","Cold-temperature altimeter corrections","Why a pressure altimeter over-reads in cold air, leaving you lower than indicated, and how to correct minimum altitudes for temperature on an approach in mountainous or freezing conditions.",4,{"path":293,"title":294,"description":295,"date":214,"topic":283,"draft":216,"minutes":291,"series":270,"seriesOrder":270},"\u002Flearn\u002Fmode-s-and-ads-b-explained","Mode S and ADS-B explained","How Mode S adds a 24-bit address, selective interrogation and a data link to the transponder, the difference between elementary and enhanced surveillance, and how ADS-B broadcasts your GPS position.",{"path":297,"title":298,"description":299,"date":214,"topic":283,"draft":216,"minutes":300,"series":270,"seriesOrder":270},"\u002Flearn\u002Fthe-global-reporting-format-for-runway-conditions","The Global Reporting Format for runway conditions","How the Global Reporting Format (GRF) describes a contaminated runway, including the runway condition code (RWYCC) from 6 to 0, the assessment matrix (RCAM), and how the report is split into thirds.",5,{"path":302,"title":303,"description":304,"date":305,"topic":306,"draft":216,"minutes":307,"series":270,"seriesOrder":270},"\u002Flearn\u002Ficao-vs-iata-codes","ICAO vs IATA codes explained","The difference between the 4-letter ICAO location indicators used for flight planning and weather and the 3-letter IATA codes on your boarding pass, plus airline codes and callsigns.","2026-06-20","Briefing",3,1781989190483]