{"id":15618,"date":"2026-05-18T19:28:45","date_gmt":"2026-05-18T13:58:45","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=15618"},"modified":"2026-07-19T16:20:03","modified_gmt":"2026-07-19T10:50:03","slug":"cp-pnr","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/cp-pnr\/","title":{"rendered":"Critical Point &#8211; Point of Safe Return"},"content":{"rendered":"<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-1.png\" alt=\"\"\/><\/p>\n<p>Critical Point (CP), also known as the Equal Time Point (ETP), is the position along a route where the time required to continue to the destination equals the time required to return to the departure aerodrome. Point of No Return (PNR), also known as the Point of Safe Return (PSR), is the farthest point an aircraft can fly while still having sufficient usable fuel to safely return. Both CP and PNR are essential flight planning concepts that help pilots make safe and informed decisions during normal operations and emergency situations.<\/p>\n<h3>Introduction to Critical Point<\/h3>\n<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-2.png\" alt=\"\"\/><\/p>\n<ul>\n<li>Critical Point is also called <strong>Point of Equal Time (PET)<\/strong> or <strong>Equal Time Point (ETP)<\/strong>.<\/li>\n<li>Critical Point is calculated for engine failure or other dire emergencies.<\/li>\n<li>In an emergency, the CP helps pilots decide whether to return to the departure airfield or continue to the destination.<\/li>\n<li>Critical Point is the position along the track between two airfields.<\/li>\n<li>From the Critical Point, the aircraft can reach either airfield in the same amount of time.<\/li>\n<li>At the Critical Point, <strong>Time Onward = Time Home<\/strong>.<\/li>\n<li>Critical Point is calculated when no suitable en-route diversion airfields are available.<\/li>\n<li>Fuel available does not affect Critical Point calculations.<\/li>\n<li>Wind direction and speed change the position of the Critical Point.<\/li>\n<\/ul>\n<h3>Critical Point Formula<\/h3>\n<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-3.png\" alt=\"\"\/><\/p>\n<p>The Critical Point is the location where the flying time to the departure and destination are equal.<\/p>\n<p><strong>Time to Return = Time to Continue<\/strong><\/p>\n<p>This principle forms the basis of all Critical Point calculations.<\/p>\n<h3>Effect of Wind and True Air Speed (TAS)<\/h3>\n<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-4.png\" alt=\"\"\/><\/p>\n<ul>\n<li>In nil wind conditions, the Critical Point is exactly halfway between departure and destination.<\/li>\n<li>The Critical Point always moves <strong>towards the wind<\/strong>.<\/li>\n<li>A headwind on the outbound leg moves the Critical Point closer to the destination.<\/li>\n<li>Ground speed on the return leg increases.<\/li>\n<li>A tailwind on the outbound leg moves the Critical Point closer to the departure airfield.<\/li>\n<li>Ground speed on the return leg decreases.<\/li>\n<li>The amount of movement depends on the headwind or tailwind component.<\/li>\n<li>An increase in True Air Speed (TAS) reduces the effect of wind.<\/li>\n<li>In practice, the effect of TAS is generally negligible.<\/li>\n<\/ul>\n<h3>Engine Failure Critical Point<\/h3>\n<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-5.png\" alt=\"\"\/><\/p>\n<ul>\n<li>The Critical Point is normally calculated using the reduced TAS following an engine failure.<\/li>\n<li>After an engine failure, the aircraft will drift down to a lower altitude.<\/li>\n<li>The aircraft will continue at a reduced True Air Speed and Ground Speed.<\/li>\n<li>The all-engines Critical Point is usually very close to the reduced-TAS Critical Point.<\/li>\n<li>Flying time to either airfield increases because of the lower TAS.<\/li>\n<\/ul>\n<h2>Point of No Return (PNR)<\/h2>\n<h3>Introduction<\/h3>\n<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-6.png\" alt=\"\"\/><\/p>\n<ul>\n<li>Point of No Return (PNR) is also known as the <strong>Point of Safe Return (PSR)<\/strong>.<\/li>\n<li>PNR is the maximum distance that can be flown along the route while still allowing a safe return with the available fuel.<\/li>\n<li>The aircraft must be able to safely return to the departure airfield.<\/li>\n<li>PNR is calculated using the aircraft&#8217;s <strong>Safe Endurance<\/strong>.<\/li>\n<li>Safe Endurance = Total Endurance \u2212 Reserve Endurance.<\/li>\n<li>PNR calculations are commonly used for flights without suitable alternate aerodromes.<\/li>\n<\/ul>\n<h3>Point of No Return Formula<\/h3>\n<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-7.png\" alt=\"\"\/><\/p>\n<p>The aircraft must have sufficient fuel to fly to the PNR and safely return.<\/p>\n<p><strong>Safe Endurance = Outbound Flight Time + Inbound Flight Time<\/strong><\/p>\n<p>This principle is used to derive the Point of No Return formula.<\/p>\n<p>In nil wind conditions, the outbound and inbound distances are equal.<\/p>\n<h3>Alternate PNR Formula<\/h3>\n<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-8.png\" alt=\"\"\/><\/p>\n<ul>\n<li>PNR can also be calculated using outbound and inbound fuel flow.<\/li>\n<li>Safe Endurance equals the fuel consumed during both the outbound and inbound sectors.<\/li>\n<li>Fuel consumption should be expressed as fuel used per unit distance.<\/li>\n<li>This method is used to derive the alternate Point of No Return formula.<\/li>\n<\/ul>\n<h2>Comparison between Critical Point (CP) and Point of No Return (PNR) <\/h2>\n<p><img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-planning\/f1-critical-point-and-point-of-safe-return-9.png\" alt=\"\"\/><\/p>\n<h3>Point of Equal Time or Critical Point<\/h3>\n<ul>\n<li>Provides the shortest flying time to the nearest airfield.<\/li>\n<li><strong>Distance to CP = D \u00d7 H \/ (O + H)<\/strong><\/li>\n<li>Endurance is not a factor.<\/li>\n<li>Distance is the important parameter.<\/li>\n<li>Used primarily during emergencies.<\/li>\n<li>The Critical Point moves into the wind.<\/li>\n<\/ul>\n<h3>Point of No Return (PNR)<\/h3>\n<ul>\n<li>Maximum distance that can be flown with usable fuel.<\/li>\n<li><strong>Time to PNR = E \u00d7 O \u00d7 H \/ (O + H)<\/strong><\/li>\n<li>Endurance is the critical factor.<\/li>\n<li>Distance is not the primary consideration.<\/li>\n<li>Used as part of normal flight planning.<\/li>\n<li>PNR is greatest in nil wind conditions.<\/li>\n<li>Any headwind or tailwind reduces the PNR distance.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Critical Point (CP), also known as the Equal Time Point (ETP), is the position along a route where the time required to continue to the destination equals the time required to return to the departure aerodrome. Point of No Return (PNR), also known as the Point of Safe Return (PSR), is the farthest point an aircraft can fly while still having sufficient usable fuel to safely return. Both CP and PNR are essential flight planning concepts that help pilots make safe and informed decisions during normal operations and emergency situations.&hellip;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"disable_featured_image":false,"footnotes":""},"categories":[356],"tags":[],"class_list":["post-15618","post","type-post","status-publish","format-standard","hentry","category-flight-planning"],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/15618","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/comments?post=15618"}],"version-history":[{"count":4,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/15618\/revisions"}],"predecessor-version":[{"id":16559,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/15618\/revisions\/16559"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=15618"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=15618"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=15618"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}