{"id":7527,"date":"2024-03-04T21:49:34","date_gmt":"2024-03-04T13:49:34","guid":{"rendered":"https:\/\/tommykwan.com\/blog\/?p=7527"},"modified":"2026-03-17T12:52:55","modified_gmt":"2026-03-17T04:52:55","slug":"why-fly-to-low-watch-below-high-to-cold-watch-below","status":"publish","type":"post","link":"https:\/\/tommykwan.com\/blog\/aviation\/why-fly-to-low-watch-below-high-to-cold-watch-below\/","title":{"rendered":"Why “Fly to low, watch below ; High to cold, watch below” ?"},"content":{"rendered":"

Ref Ace the technical pilot interview 2\/E<\/p>\n

 <\/p>\n

Ans:<\/p>\n

Always remember : <\/span><\/p>\n

aneroid barometer is working based on MSL pressure (i.e pressure height) !<\/strong><\/span><\/p>\n<\/blockquote>\n

 <\/p>\n

1.  FL formula<\/strong><\/span><\/p>\n

Flight Level (Pressure Height)<\/a><\/strong><\/span> in feet = ELEV + (1013 – QNH) * 30<\/strong><\/span><\/p>\n

 <\/p>\n

Example:<\/p>\n

Now say altimeter show 300 feet @ 1025 setting,<\/p>\n

if fly to 1015 area (high to low)<\/p>\n

<\/p>\n

So, high to low, watch below<\/p>\n

 <\/p>\n

2.  feet, temp and altitude pressure equation<\/strong><\/span><\/p>\n

feet = 96 * (absolute temperature \/ altitude pressure)<\/strong><\/span><\/p>\n

 Notes : this is just a formula found online, need to be checked for the correctness!<\/p>\n

Example:<\/p>\n

say 15C and 1013 mb, feet = 96*(15+273\/1013) = 27.3 ft<\/p>\n

when fly to 1 C and feet no change, then<\/p>\n

27.3 = 96 *( 1+273 \/ altitude pressure)<\/p>\n

0.2843 = (274\/altitude pressure)<\/p>\n

altitude pressure * 0.2843 = 274<\/p>\n

altitude pressure = 963.77<\/p>\n

That is from 15 C to 1 C area , same height (27.3 ft) , it experiences altitude pressure drop<\/p>\n

So, hot to cold = high to low => Watch below~<\/p>\n

 <\/p>\n

Another more easy way, in fact, we can observe it from error rectification table:<\/p>\n

<\/p>\n

https:\/\/skybrary.aero\/articles\/altimeter-temperature-error-correction<\/p>\n

When To Apply Corrections for temperature<\/strong> error?<\/h3>\n

As a general rule, when the aerodrome temperature is 0\u00b0C<\/strong> or colder, the temperature error correction must<\/strong> be added to all published minimum IFR altitudes<\/p>\n","protected":false},"excerpt":{"rendered":"

Ref Ace the technical pilot interview 2\/E   Ans: Always remember : aneroid barometer is working based on MSL pressure (i.e pressure height) !   1.  FL formula Flight Level (Pressure Height) in feet = ELEV + (1013 – QNH) * 30   Example: Now say altimeter show 300 feet @ 1025 setting, if fly Read More<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[64,65],"tags":[],"class_list":["post-7527","post","type-post","status-publish","format-standard","hentry","category-aviation","category-bak"],"_links":{"self":[{"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/posts\/7527","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/comments?post=7527"}],"version-history":[{"count":15,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/posts\/7527\/revisions"}],"predecessor-version":[{"id":10397,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/posts\/7527\/revisions\/10397"}],"wp:attachment":[{"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/media?parent=7527"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/categories?post=7527"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tommykwan.com\/blog\/wp-json\/wp\/v2\/tags?post=7527"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}